WO1997014443A1 - Magnetically labeled chemoattractants as targeted contrast agents in the nmr imaging of living tissues - Google Patents

Abstract

The present invention addresses magnetically labeled chemoattractants, e.g. chemotactic peptides, for the detection and investigation of diseased or disordered tissue sites or organs in the body of human and animal patients. The chemotactic peptides have the general formula: N(X)-Y-Leu-Phe-Z-A-W wherein (X) is H or a protective group such as formyl, acetyl, t-Boc, or the like; Y is Nle or Met; Z is a chemical bond, an aminoacid or an oligopeptide, e.g. (N( gamma ))Lys, Ile, Asp, Nle-Tyr-Lys, or (Gly)n, n being 1 to 4; A is a linker; and W is a suitably derivatized paramagnetic macrocyclic chelate or magnetic particle. The invention also concerns physiologically acceptable administrable compositions or formulations comprising the labeled chemoattractants, methods for preparing the chemoattractants and the formulations, and methods of using the formulations for detecting, localizing and diagnosing infected or inflammatory sites, or other trauma in the organism.

Description

MAGNETICALLY LABELED CHEMOATTRACTANTS AS TARGETED CONTRAST AGENTS IN THE NMR IMAGING OF LIVING TISSUES

Field of the Invention

The present invention addresses magnetically labeled chemoattractants, e.g. chemotactic peptides, for the detection and investigation of diseased or disordered tissue sites or organs in the body of human and animal patients. By the term of "disordered sites", one wishes to include sites of infection, inflammation, or other trauma. The invention also concerns physiologically acceptable administrable compositions or formulations comprising the labeled chemoattractants, labeled white blood cells, methods for preparing the chemoattractants and the formulations, and methods of using the formulations for detecting, localizing and diagnosing infected or inflammatory sites, or other trauma in the organism. Background of the invention

The use of conjugates in which biomolecules targeted to specific sites or receptors in the organism of patients are coupled to ligands acting as signal generator means to provide diagnostically useful information has become widely known in recent years. Said ligands involve elements capable of providing signals detectable and processable into recorded data by suitable medical equipment. Such data can thereafter be displayed and interpreted by medically trained persons into diagnostically pertinent information. Useful signal generator means include, for instance radioactive emitters (radiotracers), injectable X-ray opacifiers, e.g. iodinated compounds, and magnetic contrast enhancers in magnetic resonance imnaging (MRI).

In WO-A-90/14881, there is disclosed the attachment of polyaminocarboxylic chelators to homing proteins by using bridging functional groups such as isocyanato-, isothiocyanato-, bromoacetamido-, diazo-, N-hydroxysuccini mide esters and inter-molecular or intra-molecular anhydrides.

Also, there is disclosed for instance in WO 86/01112 (T. Brown) administrable magnetic microparticles (for instance magnetite) coupled to substances having binding affinity for organic tissues. Said tissue-specific substances include antibodies neurotransmitters, hormones, metabolites enzymes, toxins, and natural or synthetic drugs. The magnetite particles are conveniently coupled to the tissue-specific substances by coating the particles with compounds (for instance biodegradable polymers) carrying reactive functional groups and linking to the tissues- specific substances through said reactive groups. The tissue-specific targeted magnetite microparticles are administerd by injection into the blood stream (or otherwise), whereby they will be transported to targeted organs or tissues where they operate as contrast enhancers in MRI investigations of said organs.

Similarly, there is disclosed in US patent 5,277,892 (B.A. Rhodes) methods and reagents for the in-vivo tagging of polymorphonuclear leukocytes (PMN), e.g. lymphocytes, with a medically useful metal ion, including radioisotopes and paramagnetic elements, and subsequent detection of the PMN trafficking and sites of concentrated leukocytes within the organism by radiodetection or MRI. In this reference, there is administered an effective amount of a formulation comprising a leukostimulatory reagent (a lectin) bound to a useful metal species under conditions allowing the reagent to attach to leukocytes, whereby the concentrations of the stimulated leukocytes are subsequently ascertained by metal detection and measuring means.

In documents WO87/05030 and WO89/01476 (D. Parker et al.) there are disclosed conjugates of polyaza-macrocycles N-substituted by electrophilic groups such as hydroxyalkyl, alkoxyalkyl, carboxyalkyl, phosphate, sulfonate, or phosphonate, and carrying antibodies designed for locating specific tissue types. The macrocycles are provided to complex with metal atoms, suitably radioisotopes of Tc, Re, Co, Cu, Au, Ag, Pb, Bi, In and Ga . After injection of the conjugates in the organism, the compounds are transported to target sites, and the metals are acting as signal sources to be detected by scintillation or other radiotracer detecting means.

In US-4, 986, 979, (A.C. Morgan et al.) there is disclosed the use of recognition agents capable of selectively interacting with leukocytes activated at an inflammation site. The recognition agent involves monoclonal antibodies and peptides capable of selectively interacting with receptors having enhanced expression on activated leukocytes. More particularly, the reference discloses an imaging method utilizing a chemotactic peptide containining an affinity label and a radionuclide label conjugated to leukocytes to in vivo target inflammation sites. The monoclonal antibodies useful in the disclosed method are directed against epitopes on cell surface antigens which are up-regulated upon leukocyte activation. In this reference, labeling is effected by linking a signal generating moiety containing a radionuclide to the recognition agent. Examples of radionuclides are ¹¹¹In, ¹⁹⁸Au, ¹¹³Ag, ¹¹¹Ag, ¹²³I, ¹²⁵I,

¹³⁰I, ⁴⁷SC, ⁹⁰Y, ¹⁰⁰Pd, ⁶⁷Ga, ⁶⁴Cu, ⁶⁷Cr, ⁹⁹Tc; and others. The reference also provides Examples of chelating compounds to complex the radionuclides and methods to attach the chelatants to the target head of the recognition agent.

WO93/17719 and WO94/19024 (R.T. Dean; Diatech Inc.) disclose ⁹⁹Tc labeled peptides for diagnostic imaging. The peptides are selected to target sites in-vivo, i.e. to specifically bind to sites of infection and inflammation, or also to thrombotic, atherosclerotic or tumoral sites. The reference particularly discloses a specific peptide and a bisamino-bisthiol radiolabeled moiety covalently linked to the peptide via amide bond. The reference also discloses methods for radiolabeling the targeted peptides by reacting with ^99mpertechnetate in the presence of a reducing agent such as dithionite, or Sn^2+, or Fe²⁺, as well as a solid state method for making the peptide, and a method of using the radiolabeled peptide for diagnostically image various organs.

EP-A-0 398 143 (A.J. Fischman et al.; The General

Hospital Corp.) discloses labeled chemotactic peptides to image focal sites of infection or inflammation. The labeled peptides described in this reference are schematized by the formula

N(X)-Y-Leu-Phe-Z-W where X is a protective formyl, acetyl or t-Boc group; Y is methionine or norleucine; W is a label, e.g. an EDTA or DTPA chelate of a radioactive or paramagnetic isotope covalently attached to the peptide, and Z is a bond or a linker, e.g. Lys or Nle-Tyr-Lys. The reference also describes the injection of the radioactive labeled chemotactic peptides into experimental rats previously infected in the thighs with strains of E . col i , and the subsequent localization of the infection sites by hourly serial γ-camera images.

Although the achievments of the prior art have merit in the field of detection and evaluation of sites of ailment in living organisms, they still have drawbacks related to the well known health hazards of using radioactive materials for diagnostic investigations. Furthermore, the use of EDTA and DTPA chelates to complex paramagnetic species is considered undesirable regarding physiological acceptability as they tend to be unstable in-vivo, either as the result of acid-catalyzed decomplexation, or competitive chelate binding of Ca⁺² in serum, or competition from transferrin (S.M. Moerlein et al.: Int. J. Nucl. Med. Biol. 8 (1981).

Summary of the Invention

In order to remedy the foregoing drawbacks, the present invention proposes novel conjugates of chemotactic peptides with paramagnetic macrocyclic chelates or magnetite particles .

The novel conjugates have the general formula (F): N(X)-Y-Leu-Phe-Z-A-W (F) wherein (X) is H or a protective group such as formyl, acetyl, t-Boc, or the like; Y is Nle or Met; Z is a chemical bond, an aminoacid or an oligopeptide, e.g. (N(γ))Lys, Ile,

Asp, Nle-Tyr-Lys, or (Gly)_n, n being 1 to 4; A is a linker; and W is a suitably derivatized paramagnetic macrocyclic chelate or magnetic particle.

Brief description of the drawings

Fig. 1 is a graph showing the results of competition binding experiments using native and Gd-labeled chemotactic peptides.

Fig. 2 is a graph showing the variation of binding strength of Gd-labeled peptides in function to the Gd-formyl interatomic distance.

Fig. 3 is a graph showing PMNs intensity response in function to Gd-labeled peptide concentration.

Fig. 4 is a schematic representation of Gd-labeled molecules/cell association using PMNs and labeled peptides.

Fig. 5 is a schematic representation of the uptake of ^99mTc-DTPA and Gd-labeled peptide in infected and non-infected muscle.

Fig. 6 (a and b) are graphs showing the rate of reduction of NBT by human PMN stimulated by magnetite- labeled hexapeptide. Detailed Description of the Invention

The general structure of the macrocyclic ligand to form paramagnetic macrocyclic chelates (W) is preferably selected from the derivatives of 1,4,7,10-tetraazacyclododecane ring compounds of formula I

in which X is an alkyl substituent carrying one or more oxygen containing functions (e.g. OH, CO, COOH). Compound I has further acetoxy groups affixed to the N atoms and, optionally, other oxygen containing alkyl substituents. Compounds I useful in the present invention are disclosed in K. Kumar et al. J. Liquid. Chromatography 17 (1994), 3735-3746. Preferred compounds are those in which X is H (DO3A), acetoxy (DOTA), -CH₂-CHOH-CH₃ (HP-DO3A, gadoteridol, PROHANCE®) and -CH(CH₃)COOH (DOTMA). Other suitable macrocyclic chelates are disclosed in documents WO87/05030 and WO89/01476 incorporated herein by reference.

Another class of macrocyclic chelates useful in the present invention is that derived from starburst® dendrimers of the following structure (II):

in which at least one R is A of formula (F), the other

R's being derivatized chelates of paramagnetic metals, e.g.isothiocyanato-DTPA (ITC-DTPA), SCN-Ph-NH-CO-CH2-DO3A (IPA-DO3A), or having the formula

,

AcO- designating an acetate group.

The foregoing dendrimer chelatants are disclosed in detail in the publication of E.C.Wiener et al., Magnetic Resonance in Medicine 31 (1994), 1-8, which is incorporated herein by reference.

As detailed hereafter, the chelates or chelatant molecules are suitably derivatized to carry groups to effect bonding in the preparation of the magnetically labeled chemoattractants of the invention.

The paramagnetic metal ions are conveniently selected from lanthanides (for instance Gd and other lanthanides) and suitable transition elements such as Mn, Co, Ni, Cr, Fe, Cu and the like.

The linker A can be selected from chemical sequences having required functions to achieve a conjugation bridge between the peptides and the macrocyclic chelate molecules. Preferred linkers are selected from substituents attached, or to be attached, to the carbon or nitrogen atoms of the chelatants and carrying reactive functions capable of bonding to native or derivatized aminoacid acceptor groups of the chemotactic peptides (e.g. -SH, -OH, -COOH, NH₂, and the like).

Suitable linkers are well known to skilled people in the field and can include bonding units and sequences such as for instance -S-, -NH-, -NHN=, NHCONHN=, NHCSNHN=,

, NC(O)-, NC(S)-, -CO-, Het1, -C(Het2)CH2

As a non-limiting illustration, DO3A can be successively converted to its p-aminophenyl- and p-iothiocyanatophenyl-acetamido derivatives according to the following scheme:

According to the technique illustrated above, the coupling of the chelate with the peptide (designated by R) is effected by reacting the isothiocyanato function with a terminal amino function of the peptide.

According to an alternative technique, the coupling is effected directly on the acetylamino-p-aminophenylderivative of the chelatant in the presence of triethylamine, a carboxylic functions of the peptide (designated here by R) being activated by (benzotriazol-1-yl)-tris-(dimethylamino)phosphonium hexafluorophosphate (BOP). This is illustrated below:

In the above techniques, the paramagnetic ion can be introduced at an intermediate stage or after the final stage if appropriate protecting groups are used.

Other coupling methods are possible in the present invention, a few non-limiting examples being briefly summarized below (R = peptide, R' = chelatant):

Peptide N-hydroxysuccinimide carboxylate ester and aminoderivatized chelatant molecule H₂—R'

Sulfo-SMBP (4- (4-maleinimidophenyl)-N-sulfosuccinimidyl butyrate, aminoderivatized chelatants H₂R'

and HS—peptides

Chelatants mixed anhydrides R'-CO-O-CO-R' (obtained from chelatant tetramethylguanidine salts and isobutyl chloroformate) and peptides having lysine functional -NH₂.

Peptides thiolated by 2-iminothiolane , aminoderi

vatized chelatants H₂N—R', and succinimidyl-4-(N-maleinimidomethyl)-cyclohexane-1-carboxylate

Derivatization of chelatant R' by reaction of intra- or intermolecular cyclic anhydride R'-CO-O-CO-R' with alkylene diamine, introduction of a 2-pyridyldisulfide group with N-succinimidyl-3-(2-pyridyldithio)-propionate (SPDP) and coupling with thiolated chemotactic peptide to form a covalent thia-bonded conjugate, this being as follows:

R'CONH-Alk-NH₂ + SPDP ➨ R'CONH-Alk-NH-CO-CH₂-SSPyr R'CONH-Alk-NH-CO-CH₂-SSPyr + RSH ➨ R'CONH-Alk-NH-CO- CH₂-SR For coupling magnetically responsive particles, e.g. ferromagnetic or superparamagnetic particles derived from ferrites or magnetites, the latter are derivatized with materials to become linker A or to effect bonding with linker A. This can be accomplished for example by first coating the particles with a polymeric material provided (or to be provided later) with functional groups capable of bonding with the chemoattractant peptides. Within the bounds of this embodiment, the linking techniques are similar to those disclosed herebefore. For instance, the magnetic particles can be coated with derivatized polyacrylics, polystyrenes, dextran and other polysaccharides. All details concerning applying water insoluble coatings on magnetic particles to which bioactive proteins can be covalently coupled are provided in documents US-4,070,246 (J.F. Kennedy et al.; Abbott Laboratories) and US-4, 157323 (S.Y. Shiao-Ping et al.; Cal Tech), both being incorporated herein by reference.

According to a different strategy also applicable to the magnetic particles of the present invention, the latter are silanized with compounds provided with functions capable of binding to proteins, with or without the assistance of additional intermediate sequences. For instance, silanizazion can be carried out using reactive trialkoxysilanes such as isocyanatoalkylsilanes, isothiocyanoalkylsilanes, 3-aminopropyltrimethoxysilane, hydroxypropyltriethoxysilane, 4-chlorobutyltrimethoxysilane and the like. All details about silanization of magnetic particles (including also the preparation of the particles themselves from iron salts solutions) are found for instance in document EP-125 995 (M.S. Chagnon et al.; Advanced Magnetics) incorporated herein by reference. Once the manetic particles have been silanized they can be coupled to the chemotactic peptides by the same means disclosed above in the case of the paramagnetic chelates.

In an other embodiment involving magnetic particles, the latter are coated with a phospholipid and an amphiphilic copolymer having lipophilic (POP) and hydrophilic (PEG) segments (see EP-A-607 401 incorporated herein by reference) . The block copolymer is derivatized with functions capable of linking to proteins and peptides such as the chemotactic peptides of the present invention. Derivatised block copolymers such as Pluronic® and Synperonic® are illustrated in WO-A-95 06251 (University of Utah) which discloses derivatized Pluronic® and Tetronic® compounds carrying reactive groups at the end of the PEG blocks. In this document, the derivatized copolymers are used to coat by adsorption hydrophobic surfaces (e.g. polystyrene beads and similar carriers), which coated surface then function as substrates for immobilizing proteins and alike substances. In the present invention, the following derivatized amphiphilic copolymers have been syn-thesized

in which the code F108 designates a Pluronic® amphiphilic polyoxyethylene-polyoxypropy lene copoly-mer. These derivatized amphiphiles can be used as linker A in formula (F) to couple magnetite particles coated with phosphatidic acid, and the chemotactic peptides

The following examples illustrate the invention.

Example 1 Synthesis of N (γ)-[[[-4-[[[ 1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-10-yl]acetyl]amino]phenyl]amine]thiocarbonyl]-N-(N-formyl-L-norleucyl-L-leucyl-L-phen ylalanyl-L-norleucyl-L-tyrosyl)-L-lysine, monogadolinium salt [Gd(for-Nle-Leu-Phe-Nle-Tyr-(N(γ)Lys-IPA-DO3A)]

A. Preparation of 10-[N-(4-Nitrophenyl)-acetamido- 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid

A solution of 2-chloro-4'-nitroacetanilide (3.0 g, 14 mmol) in DMSO (30 mL) was slowly added to an aqueous solution of 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) (5.8 g, 16.8 mmol) in water (30 mL) at pH 10. The reaction mixture was maintained at pH 10±0.5 by the addition of 10M NaOH and at 50°-60°C for 54 h. The resultant yellow precipitate was removed by filtration and dissolved in water (150 mL). The pH of the aqueous solution was adjusted to ca 2 by the addition of 1.0N HCI. The resultant solution was then loaded on a CHP-20P column (wet volume, 600 ml). The column was eluted with water (3L), 5% (IL), 10% (IL) and 20% (1.5L) of EtOH in sequence. The fractions containing the product (which were eluted by 20% ethanol) were combined and concentrated in vacuo. 10-[N-(4-nitropheny)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (2.6 g, 35.4%) was obtained as a yellow solid. Anal. Calcd. for C₂₂H₃₂N₆O₉.1.30 H₂O: C, 48.23; H, 6.36; N, 15.34. Found: C, 47.94; H, 6.48; N, 15.72; H₂O, 4.26 % (desorption Karl-Fisher); ¹H NMR (d₆-DMSO) : 8 2.7-3.7

(m, 24H, ring and acetate methylenes), 4-7 (very broad, COOH), 8.01(d, 2H, ortho H'S), 8.17 (d, 2H, meta H's), 11.03 (s, 1H, CONH); FAB-MS: m/e: 525 (M+H)⁺; 509 (M-O)⁺; IR (KBr) : 3424, 1631, 1505 and 1333 cm-.¹ B. Preparation of: 10-[N-(4-nitrophenyl)-acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium salt A solution of gadolinium acetate (602 mg, 1.48 mmol, 1.33 equiv) in water (3.5 mL) was added to a suspension of 10-[N-(4-nitropheny)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-tri-acetic acid (580 mg, 1.114 mmol) in water (5 mL) at 65°C. Initially, a clear solution was obtained, but after 25 min, a pale yellow solid precipitated. Filtration and washing of the solid with water (2 × 2 mL) gave the gadolinium chelate in 62% yield (470 mg). An additional 210 mg of the product was obtained by CHP20 chromatography for the filtrate, giving a final combined yield of 90%. Anal. Calcd. for C₂₂H₂₉N₆O₉Gd 0.69 H₂O: C, 38.23; H, 4.43; N, 12.16. Found: C, 38.34; H, 4.48; N, 12.09; H₂O, 1.80% (desorption Karl-Fisher); FAB-MS: m/e : 679 [ (M+H) ⁺, ¹⁵⁸Gd], 340 [(M+2H⁺)²⁺, ¹⁵⁸Gd]. C. Preparation of 10-[N-(4-aminophenyl)-acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium salt

10% Pd/C catalyst (50% water-Degussa type, 1.06 g, 0.5 mmol of Pd) was added to a solution of 10-(N-(4- nitrophenyl)acetamido)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, mono gadolinium salt (3.39 g, 5 mmol) in methanol (95 mL) and water (18 mL). The solution was hydrogenated at room temperature under a hydrogen atmosphere (20-25 filtered to psi) for 10 h. The reaction mixture was filtered to remove the catalyst, and the filtrate was evaporated to dryness. The residue was crystallized from methanol to give 3.04g (93.6%) of the product. Anal. Calcd for C₂₂H₃₃N₇O₇Gd 4.18 H₂O: C, 36.49; H, 5.48; N, 11.61. Found C, 36.22; H, 5.41; N, 11.41; H2O, 10.4% (desorption

Karl-Fisher). FAB-MS: m/z: 650 [(M+H)⁺, ¹⁵⁸Gd]. IR (KBr):

3424, 1616 cm^-1. D. Preparation of 10-[N-(4-Isothiocyanatophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium salt A solution of thiophosgene (70.9 mg, 0.62 mmol) in CHCl₃ (3 mL) was added to a solution of 10-[N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium salt (100 mg, 0.15 mmol) in water (4 mL). The biphasic mixture was stirred at room temperature and the progress of the reaction was monitored by HPLC using a Nucleosil C₁₈ column. When the conversion to the expected product was completed, the aqueous layer was separated and the pH (1.5) of this solution was adjusted to 5.2 by the addition of 1.0 N NaOH. This solution was then applied to a CHP20 column (2.5 × 15 cm). The column was eluted with water and water containing 2.5, 5.0, 7.5, 10, 20 and 40% EtOH, in the sequence indicated. The fractions which contained the product were combined and evaporated in vacuo at ambient temperature to remove EtOH, then lyophilized to give the product (75 mg, 70.5% yield) as a white solid. Anal. Calcd. for C₂₃H₂₉N₆O₇SGd: 5.35 H₂O 0.16 Gd (APA-DO3A) : C, 35.15; H, 5.16; N, 10.76; S, 3.49. Found: C, 35.23; H, 5.03; N, 10.56; S, 3.03; H₂O, 12.24 % (desorption Karl-Fisher). FAB-MS: m/e : 692 [(M+H)+ ¹⁵⁸Gd] , 648 [(M-CO₂)+, ¹⁵⁸Gd]. IR (KBr): 3424, 2114(N=C=S) and 1609 cm^-1.

E. Preparation of N(γ)-[[[-4-[[[1,4,7-Tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-10-yl]acetyl]amino]phenyl]-amine]thiocarbonyl]-N-(N-formyl-L-norleucyl-L-leucyl-L-phenylalanyl-L-norleucyl-L-tyrosyl)-L-lysine, monogadolinium salt

Thiophosgene (100mL) was suspended in chloroform (0.5 mL) and was mixed with the gadolinium salt of 10-[N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (53.06 mg, 0.0798 mmol). The biphasic mixture was stirred vigrously for 90 min at room temperature. The aqueous phase was separated from the chloroform layer and the pH was adjusted to 7 with sodium hydroxide. The chloroform layer was washed with water carefully, and the aqueous extracts were combined. The formation of 10-[N-(4-isothiocyanatophenyl)-acetamido] -1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium salt was confirmed by a reversed-phase HPLC analysis.

N-Formyl-L-norleucyl-L-leucyl-L-phenylalanyl-L-norleucyl-L-tyrosyl-L-lysine (79.8 mg, 0.074 mmol) was dissolved in dimethyl formamide/triethyl amine (99:1, 8.0 mL) and the pH of the peptide was adjusted to 9.0. The peptide was mixed with the aqueous solution of the isothiocyanato compound. Some insoluble material was seen upon the progress of the reaction which was dissolved by addition of more base and/or DMF. The reaction mixture was stirred for 18 h. At the end of this period the reaction mixture was analyzed by an HPLC method, which confirmed the completion of the reaction. The crude material was purified by a semi-prep HPLC gradient method by using a PLRP-S column. The fractions were collected and the volume of the purified material was reduced at 40°C under the stream of nitrogen. The concentrated solution was lyophilized to a solid material (60 mg overall yield 51.4%) which was analyzed by mass spectral analysis. FAB-MS: m/z: 1515 [(M+H)⁺ with gadolinium pattern. Anal. Calcd. for C₆₆H₃₄N₁₃O₁₆SGd Na 6 H₂O: C, 48.12; H, 6.50; N, 11.05; Found: C, 40.21; H, 6.72; N, 10.96; FAB-MS: m/e : 1515 [(M+H)⁺¹⁵⁸Gd . Example 2

Synthesis of N(γ)-[ [[-4-[[[1,4,7,-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-10-yl]-acetyl]amino]phenyl]- amine]thocarbonyl]-N-(N-formyl-L-norleucyl-L-leucyl-L-phenylalanyl-L-norleucyl-L-tyrosyl)-L-lysine, monogadolinium-153 salt [Gd-153 (for Nle-Leu-Phe-Nle-Tyr-(N()γLys-IPA-DO3A)]

A. Preparation of 10-[N-(4-aminophenyl)-acetamido- 1,4,7, 10-tetraazacyclododecane-1,4,7-triacetic acid monotriethyl-ammonium salt

A solution of 10-[N-(4-nitrophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-tri-acetic acid, (Example la, 5.3 g, 10.1 mmol) in water (150 ml) was prepared, and pH was adjusted to 7.0. To this solution was added 10% Pd/C catalyst (50% water Degussa type, 2.17 g, 1.0 mmol of Pd). The solution was hydrogenated at room teperature under a hydrogen atmosphere (20-25 psi) for 3 h. The reaction mixture was filtered to remove the catalyst. The residue obtained after removal of the solvent from the filtrate was applied to a DEAE Sephadex column (5 × 20 cm). The column was eluted with 5, 10, 25, 40, 80 and 100 mM of triethylammonium bicarbonate (TEAB) buffer (1 L of each solution). Each fraction was monitored by HPLC and conductivity. Removal of the buffer from the fractions containing the desired compound (which was eluted by the 100 mM TEAB solution) gave the product (4.2 g, 70% yield) as the mono-triethylammonium salt. Anal. Calcd. for C₂₈H₄₉N₇O₇: 1.91 H₂O 0.34 N(C₂H₅)3: C, 54.29; H, 8 78, 15.47. Found: C, 53.92; H, 9.18; N, 15.58; H₂O, 5.45 % (desorption Karl-Fisher). ¹H-NMR (D₂O) : δ 1.25 (t, CH₃CH₂N), 3.15 (t, CH₃CH₂N), 3.0 - 3.9 (m, 24H, ring and acetate methylenes), 6.84 (d, 2H, meta H's), 7.27 (d, 2H, ortho H's). ¹³C-NMR (D₂O) : 8.04 (CH₃CH₂N) 46.44 (CH₃CH₂N), 48.05, 50.48, 51.60, 55.24, 55.67, 56.20 (ring and acetate methylenes); 116.78 (C3), 123.30 (C2), 128.70 (C4), 142.73 (C1) ; 169.65, 170.25, 177.76 (CO). MS (FAB): m/e : 495 (M+H)⁺, 102 [HN(C₂H₅)₃]⁺. IR (KBr): 3437, 2976, 2940, 1628, 1514 and 1398 cm^-1.

B. Preparation of 10-[N-(4-Amino-phenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic,monogadolinium-153 salt

A solution of carrier-added ¹⁵³GdCl₃ (504 mCi, 0.126 mmol) was mixed with 10-[N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane 1,4,7-triacetic acid triethyl ammonium salt (Example 2a, 76.43 mg, 0.12 mmol). The reaction mixture was heated and the pH of the solution was raised very slowly to 7. The reaction mixture was analyzed by a reversed phase HPLC/analytical method, which confirmed the formation of the product (by comparison to the compound of example lc). The reaction mixture was reduced to approximately 3 mL and was transferred to a vial.

C. Preparation of N(γ)-[[[1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-10-yl]acetyl]amino]-phenyl]- amine]thiocarbonyl]-N-(N-formyl-L-norleucyl-L-leucyl-L-phenylalanyl-L-norleucyl-L-tyrosyl)-L-lysine, monogadolinium-153 salt The gadolinium-153 salt of 10-[N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (Example 2b) was added to a mixture of thiophosgene (150 mL) and chloroform (2.0 mL). The biphasic reaction mixture was stirred vigrously for 40 min at room temperature. The aqueous phase was separated from the chloroform layer and the pH was adjusted to 7 with sodium hydroxide. The chloroform layer was washed with additional water. The formation of 10-[N-(4-isothiocyanatophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, monoagadolinium-153 salt was confirmed by a reverse-phase HPLC analysis. The recovery of the conversion was 95%. N-formyl-L-norleucyl-L-leucyl-L-phenylalanyl-L-norleucyl-L-tyrosyl)-L-lysine (64.81 mg, 0.0795 mmol) was dissolved in dimethyl formamide/triethylamine (99:1, 10.0 mL) and the pH of the peptide was adjusted to 9.1. The peptide was mixed with the above isothiocyanate, and the reaction mixture was stirred for 18 h. At the end of this period the reaction mixture was analyzed by an HPLC method, which confirmed the completion of the reaction. The crude material was purified by a semi-prep HPLC gradient method by using a PLRP-S column. The fractions were collected and the volume of the purified material was reduced at 40°C under the stream of nitrogen to near dryness. The recovery of the purified product was 30%. Example 3

Synthesis of N(γ)-[ [[-4-[[[1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-10-yl]acetyl]amino]-phenyl]amino]thiocarbonyl]-N-(N-formyl-L-methionyl-L-leucyl-L-phenylalanyl)-L-lysine, monogadolinium salt [Gd(for-Met-Leu-Phe-(N(γ))Lys-IPA-DO3A)]

10-[N-(4-Isothiocyanatophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium salt was prepared as outlined in Example le, by reaction of 10-[N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid gadolinium salt (33.8 mg, 0.05 mmol) with thiophosgene (200 mL) in chloroform (2.0 mL). N-Formyl-L-methionyl-L-leucyl-L-phenylalanyl-L-lysine (41.48 mg, 0.05 mmol) at pH 10.1 was added to the aqueous solution of the isothicyanato compound. The pH was adjusted to 10.1 with sodium hydroxide, and the reaction mixture was stirred overnight at ambient temperature. The progress of the reaction was checked by an HPLC method. The product was purified by a semi-prep HPLC method. All fractions containing the product were collected and concentrated to a minimum volume. The sample was lyophilized to a solid material (30 mg yield 55%). The solid material was assayed for its purity by an HPLC/analytical method, which indicated 97% purity. Anal Calc. for C₅₀H₇₁N₁₁O₁₃S₂GdNa . 15 H₂O C=, 38.78; H, 6.55; N, 9.94; S, 4.14; Found: C, 38.87; H, 5.68; N, 9.54; S, 4.06. FAB-MS: m/e 1257.25 (m+H)⁺ and 1279 (m+Na)⁺.

Example 4

Synthesis of N(γ)-[[[-4-[[[1,4,7-tris(carboxymethyl)- 1,4,7,10-tetraazacyclododecane-10-yl]acetyl]amino]phenyl]- amino]thiocarbonyl]-N-(N-formyl-L-methionyl-L-leucyl-L-phenylalanyl)-L-lysine, monogadolinium-153 salt [Gd-153 (for-Met-Leu-Phe-(N(γ)Lys-IPA-DO3A)]

10-[N-(4-Isothiocyanatophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium-153 salt, Gd(IPA-DO3A) was prepared and purified by a semi-prep HPLC method as outlined in Example 2b/c. In this preparation, the following quantities were used: GdCl₃ solution (0.36 M, 0.6 mL, 0.216 mmol), ¹⁵³GdCl₃ (500 mCi, 0.73 mCi/mL, 0.329 mCi/mg Gd₂O₃, 0.0083 mmol) and 10-[N-(4-aminophenyl) acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid triethyl ammonium salt (133 mg, 0.2 mmol). The chelate was converted to 10-[N-(4 Isothiocyanato- phenyl)acetamido]-1,4,7,10-tetraazacyclodo-decane-1,4,7-triacetic acid, monogadolinium-153 salt as outlined in Example 2c.

The solution of N-formyl-L-methionyl-L-leucyl-L-phenylalanyl-L-lysine (weight, 0.167 mmol) in water (5 mL) at pH 9.5 was added to the solution of the Gd-153 isothiocyanato compound. The reaction mixture was stirred overnight. The product was purified by a semi-preparative HPLC method. All of the fractions containing the product were collected and concentrated to near dryness under the stream of N₂ at 40° C. The sample was assayed for radioactivity and purity. The recovery of the purification was calculated as 47.3%. An HPLC analysis of the sample showed one peak.

Example 5

Synthesis of 10-[( (N-Formyl-L-norleucyl-L-leucyl-L(D)-phenylalanyl)-N-(4-aminophenyl) acetamidol-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium salt [Gd(for-Nle-Leu-Phe-APA-DO3A)]

A. Preparation of trimethyl 10-[N-(4-amino-phenyl)-acetamido-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate pentahydrochloride Dry HCl gas was passed into a suspension of 10-[N-(4-aminophenyl) acetamido]-1,4,7,10-tetraazacyclododecane- 1,4,7-triacetic acid (Example 2a, 5.0 g, 10.12 mmol) in dry methanol (150 mL) at 0°C until a clear solution was obtained. The reaction mixture was kept below 20°C overnight with stirring. Evaporation of the solvent provided a thick paste which was dissolved in water and freeze-dried to afford trimethyl 10-[N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate pentahydrochloride as a colorless solid. Yield:

7.20 g (98%); mp 210-215°C; ¹H NMR (D₂O) δ 2.80-4.40 (bm),

3.71(s, COOCH₃) and 7.32 & 7.55(2d, Ar-H). FAB MS: m/e 537

(M+H)⁺. B. Preparation of trimethyl 10-[((N-formyl-L-norleucyl-L-leucyl-(D,L)-phenylalanyl)-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate A mixture of N-formyl-Nle-Leu-Phe (0.40 g, 0.95 mmol), benzotriazol-1-yloxy-tris(dimethyl-amino)phosphonium hexafluorophosphate (BOP, 0.46 g, 1.04 mmol) and trimethyl 10-[N-(4-aminophenyl)-acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate pentahydrcchloride (0.76 g, 1.04 mmol) in dry CH₂Cl₂ (10 mL) was treated with triethylamine (0.74 g, 7.31 mmol) and stirred at room temperature for 6 h under nitrogen atmosphere. The reaction mixture was then poured into water and, after adjusting the pH to ~4.00 with KHSO₄ solution, the aqueous layer was extracted with CH₂Cl₂ (3 × 50 mL). The organic phase was washed with water, dried and evaporated to afford a paste. For further purification, it was loaded onto a silica gel column and eluted with CH₂Cl₂-CH₃OH (98:2). The fractions containing the compound were combined and evaporated under vacuum to provide a foamy solid of the title compound. Yield: 0.70 g (78.3%); mp 120-124°C. TLC [silica gel, CH₂Cl₂:CH₃OH, 9:1] R_f 0.52. The HPLC showed two peaks with the difference in retention time ~2.2 min indicating the racemization. FAB MS: m/e 938 (M+H)⁺. C. Preparation of 10-[((N-Formyl-L-norleucyl-L-leucyl-phenylalanyl-N-(4-amino-phenyl)acetamidol-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid

A solution of LiOH (110 mg, 2.62 mmol) in dioxane-water (5 mL, 4:1) was added to the product in Example 5b (0.70 g, 0.75 mmol) and stirred at room temperature for 4 h. The reaction mixture was diluted to ~10 mL with water and pH of the solution adjusted to ~4.00 with KHSO₄ solution. The solution was evaporated under vacuum to afford a foamy solid. The soild was then subjected to preparative reversed-phase HPLC purification using water-acetonitrile (0.1% TFA) as eluant to separate diastereoisomers resulting from the D- and L-forms of phenylalanine. The fractions containing pure stereoisomers (>99% purity) were combined and lyophilized. The preparative HPLC conditions were as follows: Vydac C₁₈ column (2.2 × 25 cm); linear gradient, initial start from 30% ACN (0.1% TFA) in H₂O (0.1% TFA); W, 230 nm; flow rate, 10 mL/min. L-isomer: mp 135-140°C (mono CF₃COOH salt). Anal. Calcd. for C₄₃H₆₅N₉O₁₁ 2.66 H₂O, 1.06 CF₃COOH: C, 50.09; H, 6.56; 11.43; F, 7.75. Found: C, 50.09; H, 6.73; N, 11.02; F, 7.53; H₂O, 4.34 % (desorption Karl- Fisher). MS m/z 896 (M+H)⁺. D-isomer: mp 135-140°C (mono CF₃COOH salt). Anal. Calcd. for C₄₃H₆₅N₉O₁₁·2.72 H₂O, -1.05 CF₃COOH: C, 50.04; H, 6.57; 11.42; F, 7.72. Found: C, 50.04; H, 6.60; N, 11.21; F, 7.54; H₂O, 3.53 % (desoprtion Karl-Fisher). FAB MS m/e 896 (M+H)⁺.

Example 6 Synthesis of 10-[ ( (N-formyl-L-methionyl-L-leucyl-L-phenylalanyl)-(aminohenyl)-N-4-acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium salt, [Gd(for-Met-Leu-Phe-APA-DO3A)]

A. Preparation of trimethyl 10-[((N-formyl-L-methionyl-L-leucyl-L-phenylalanyl)-N-(4-aminophenyl)-acetamidol-1,4,7 ,10-tetraazacyclododecane-1,4,7-triacetate

Trimethyl-10-[N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate pentahydrochloride (172.4 mg, 0.24 mmo, Example 5a) in DMF (2 mL) was reacted with Et₃N (121.4 mg, 1.2 mmol) for 20 min. After N-formyl-Met-Leu-Phe (105 mg, 0.24 mmol), BOP (122 mg, 0.28 mmol) and Et₃N (78 ml, 0.56 mmol) were added, the mixture was stirred at room temperature for 20 h. The reaction mixture was evaporated to dryness. The residue was dissolved in MeOH (1 ml) then purified by preparative HPLC. The fractions which contained product were combined and lyophilized to obtain the product as a white solid (91 mg, 40% yield). MP. 125-128° C. HPLC: Retention time, 14.3 min; Vydac (4.6 × 250 mm); isocratic, 30% acetonitrile (0.1% TFA) in H₂O

(0.1%TFA) (pH 2.0) W, 230 nm; flow rate, 1 mL/min. ¹H-NMR (CD₃OD) δ 0.70-0.81 (m), 1.52 & 2.48(m), 1.98(s),

3.18-4.15 (m), 4.28 & 4.39(m), 7.18-7.58(m) and 8.08(s). FAB MS: m/e 956.7 (M+ H)⁺and 978.7 (M+Na)⁺.

B. Preparation of 10-[((N-formyl-L-methionyl-L-leucyl-L-phenylalanyl)-N-(4-aminophenyl)acetamidol-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid Trimethyl-10-[((N-formyl-L-methionyl-L-leucyl-L-phenyl-alanyl)-N-(4-aminophenyl) acetamido] 1,4,7,10-tetraazacyclododecane-1,4,7-triacetate (66.9 mg, 0.07 mmol) was added to lN NaOH (MeOH, 3 mL), and the mixture was stirred at room temperature for 7 h. The reaction mixture was evaporated to dryness to remove MeOH and the residue then was dissolved in water (3.5 mL). The pH of the solution was adjusted to 4.5 by addition of KHSO₄. Water (80 mL) was added to dissolve all solid which formed during the neutralization. After filtration the filtrate was purified by a preparative HPLC method. The fractions which contained product were combined and lyophilized to obtain the product as a white solid (11 mg, 17% yield). Mp. 135-138° C. HPLC Retention time 7.1 min; Vydac-C18; (4.6 × 250 mm) column isocratic, 30% acetonitrile (0.1 % TFA) in water (0.1% TFA) ~ at 230 nm; flowrate, 1 ml/min. ¹H-NMR (CD₃OD) δ 0.67-.071

(m, 6H, CH3), 1.3 and 2.4 (m, 10H, CH₂), 1.9 (s, 3H, SCH₃), 3.19-4.22 (m, 24H, macrocyclic protons and CH₂), 4.05 and 4.45 (m, 3H, CH), 7.2-7.6 (m, 9H, benzene ring), 8.03 (s, CHO). IR (KBr): 3434, 1678, 1516 and 1204 cm^-1. FAB MS: m/e 914 (M+H)⁺. Anal.: Calcd. for C₄₃H₆₃N₉O₁₁s₁-1.45CF₃COOH 4.7g H₂O C, 47.29; H, 6.40; N, 10.81; S, 2.75; F, 7.09, Found: C, 47.29; H, 6.21; N, 10.56; S, 3.00; F, 7.09. (desorption Karl-Fisher).

C. Preparation of 10-[((N-formyl-L-methionyl-L-leucyl-L-phenylalanyl)-N-(4-aminophenyl)acetamidol-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium salt

GdCl₃ (3.6 mL of a 9.945 mM solution, 0.0358 mmol) was mixed with 10-[((N-formyl-L-methionyl-L-leucyl-L-phenylalanyl)-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (40 mg, 0.0358 mmol) in water. The reaction mixture was heated at 60°C. The pH of the reaction mixture was raised slowly to 7, while the reaction mixture was heated. When the pH of the reaction mixture reached 7, the sample was allowed to cool, and the product was purified by semi-preparative HPLC method. All fractions containing the product were collected and concentrated under a stream of nitrogen at 40°C. The final solution was lyophilized. Yield 30 mg (88%). Elemental Analysis: (Calculated for C₄₃H₆₀N₉O₁₁GdS. 7.3 H₂O) : Calcd. C= 43.04, H = 6.27, N = 10.50, and S = 2.67; Found: C = 43.15, H = 6.05, N = 10.39, and S = 2.73. FAB Mass: m/e at 1051.2 (m+H).⁺

Example 7

Synthesis of 10-[((N-formyl-L-methionyl 1-leucyl-L-phenylalanyl-glycyl)-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium salt [Gd(for-Met-Leu-Phe-Gly-APA-DO3A]

A. Preparation of trimethyl-10-r((N-t-Boc-glycyl)-N-(aminophenyl)acetamidol-1,4,7,10-tetraazacyclododecane- 1,4,7-triacetate

To a mixture of trimethyl-10-[N-(4-aminophenyl)¬acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate pentahydrochloride (2.00 g, 2.75 mmol) Boc-Gly (0.53 g, 3.03 mmol, Example 5a) and BOP reagent (1.34 g, 3.03 mmol) in dry CH₂Cl₂ (20 mL) was added triethylamine (2.14 g, 21.15 mmol) and stirred at room temperature under nitrogen atmosphere for 9 h. The reaction mixture was then poured into water, pH of the solution was then adjusted to ~4.00 using KHSO₄ solution and extracted with CH₂Cl₂ (3 × 100 mL). The combined organic layer was then washed with water, dried and evaporated on a rotary evaporator to provide a foamy solid of the title compound. For further purification, the solid was loaded onto a silical gel column as dichloromethane solution and the column was eluted with CH₂Cl₂-CH₃OH (98:2) mixture. Fractions containing the compound were collected and evaporated under vacuum to afford the product as a light yellow colored solid (1.68 g, 80%); Mp. 135-139 °C . HPLC: Retention time 22.4 min was observed under the following conditions, Vydac-C18, 4.6 × 250 mm, linear gradient, water and acetonitrile containing 0.1% TFA, 0-50% ACN in 50 min; W 230nm; flow rate 1 mL/min. ¹H-NMR (CDCl₃) δ 1.37(s), 2.10-2.35(m), 3.62(2s), 3.89(d), 5.62(bs), 7.38(m), 8.52(bs) and 8.61(bs). FAB MS: m/e 716 (M+Na)!

B. Preparation of trimethyl-10-[glycyl-N-(4-aminophenyl)acetamido-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate. TFA salt

A solution of trimethyl-10-[((N-t-Boc-glycyl)-N-(4-aminophenyl)acetamido]-1,4,7,10 tetraazacyclododecane-1,4,7-triacetate (1.6 g, 2.16 mmol) in dry CH₂Cl₂ (5 mL) was treated with trifluoroacetic acid (5 mL) and stirred at room temperature under nitrogen atmosphere for 1 h. The reaction mixture on evaporation under vacuum to remove the solvent afforded a thick paste which on trituration with dry ether provided the title compound 7 as an off white solid in near quantitative yield. Mp 178-181°C; HPLC: Retention time 17.13 min, Vydac-C18, 4.6 × 250 mm, linear gradient, water (0.l%TFA-acetonitrile (0.1%TFA), 0-50%ACN in 50 min; W 230nm; flow rate 1 mL/min. ¹H-NMR (D₂O) d 2.19-4.38 (m), 3.69(s) and 7.42(s). FAB MS: m/e 594.5 (M+H).⁺

C. Preparation of trimethyl-10-[( (N-Formyl-L-methionyl-L-leucyl-L-phenylalanyl-glycyl)-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate

A mixture of trimethyl-10-[glycyl-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraaza-cyclododecane-1,4,7-triacetate, TFA salt (1.19 g, 2 mmol), for-Met-Leu-Phe (437.6 mg, 1 mml) and BOP (885 mg, 2 mmol) in ACN (20ml) was treated with Et₃N (809.6 mg, 8 mmol) at room temperature for 2 h. The reaction mixture was evaporated to dryness. The residue was then purified by silica gel (40 g). The fractions which contained the product were combined and evaporated to obtain a yellow solid (1.08 g, 100% yield). MP 125-128° C; HPLC: retention time 17.2 min, Vydac-C18, 4.6 × 250 mm, linear gradient, water (0.1%TFA0-acetonitrile (0.1%TFA), 20-50%ACN in 30 min; W 230 nm; flow rate 1 mL/min. ¹H-NMR (CD₃OD) δ 0.81-0.91 (m), 1.52 & 2.41(m), 1.92 (s), 3.21-4.11 (m), 4.21 ~ 4.45(m), 7.23-7.61(m) and 8.08(s). FAB MS: m/e 1013(M+H)⁺ and 1035(M+Na)⁺.

D. Preparation of 10-[((N-Formyl-1-methionyl-L-leucyl-L-phenylalanyl-glycyl)-N-(4-amniophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid

Trimethyl-10-[((N-Formyl-L-methionyl-L-leucyl-L-phenyl-alanyl-glycyl)-N-(4-aminophenyl)acetamido]-1,4,7,10-tetra-azacyclododecane-1,4,7-triacetate (1.01 g, 1 mmol) was added to a solution of LiOH (240 mg, 5.7 mmol) in dioxane and water (1:1) (12 ml). The reaction was carried out at room temperature for 2 h. Water (20 ml) was added to reaction mixture and the pH of the solution was adjusted to 3-4 by addition of KHSO₄ solution. The reaction mixture was evaporated to dryness. The residue then was dissolved in water (300 ml) and purified by preparative HPLC. The fractions which contained the product were combined and lyophilized to obtain the product as a white solid (274 mg, 23% yield). Mp : 138-140 °C . TLC: R_f 0.18 in n-BuOH:AcOH :H₂O (13:2:5). HPLC: Retention time 12.2 min; Vydac-C18; (4.6 × 250 mm); linear gradient, water (0.1%TFA) and acetonitrile (0.1 % TFA), 0-50% ACN in 50 min; monitored at 230 nm; flowrate, 1 mL/min. ¹H-NMR (CD₃OD) : δ 0.7-.08 (m, CH₃), 1.5 and 2.4 (m, CH₂ ), 1.9 (s, SCH₃), 3.19-4.0 (m, macrocyclic protons and CH₂), 4.2 and 4.4 (m, CH), 7.2-7.6 (m, benzene ring), 8.0 (s, CHO). FAB MS: m/e : 971 (M+H)⁺, 993 (M+Na)⁺ and 1009 (M+K)⁺. Anal. Calcd. for C₄₅H₆₆N₁₀O₁₂s₁ 1.00 CF₃COOH 4.31 H₂O: C, 46.32; H, 6.09; N, 11.07; S, 2.53; F, 8.56, Found: C, 46.6; H, 6.01; N, 10.90; S, 2.88, F, 8.52. (desorption Karl-Fisher). E. Preparation of 10-[((N-formyl-L-methionyl-L-leucyl-L-phenylalanyl-glycyl)-N-(4-aminophenyl)acetamido]-1,4,7,10- tetraazacyclododecane-1,4,7-triacetic acid, monogadalinium

_salt

The gadolinium complex was prepared by the method outlined in example 6C. Yield 65%; elemental analysis: (Calculated for C₄₅H₆₃N₁₀O₁₂GdS 5.7 H₂O): Calcd. C= 44.02, H = 6.11, N = 11.41, and S = 2.61; Found: C = 43.94, H = 5.80, N = 11.49, and S = 2.83. FAB Mass: m/e 1126 (m+H).⁺

Example 8

Synthesis of 10-[((N-Formyl-L-methionyl-L-leucyl-L-phenylalanyl-L-isoleucinyl)-N-(4-aminophenyl)acetamido]- 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium salt [Gd(for-Met-Leu-Phe-Ile-APA-DO3A)]

A. Preparation of trimethyl-10-[((N-t-Boc-L-isoleu¬cinyl)-N-(4-aminophenyl)acetamido-1,4,7,10-tetra-azacyclododecane-1,4,7-triacetate To a mixture of t-Boc-isoleucine (1.00 g, 4.16 mmol), trimethyl-10-[N-(4-aminophenyl)-acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate pentahydrochloride (3.30 g, 4.59 mmol) and BOP reagent (2.00 g, 4.52 mmol) in dry acetonitrile (20 mL) was added triethylamine (2.29 g, 22.6 mmol) and stirred at room temperature under nitrogen atmosphere for 8 h. The reaction mixture was then treated with water (10 mL) and evaporated on a rotary evaporator to remove the solvent to afford a thick paste. The paste was then loaded onto a silica gel column as dichloromethane solution and the column was eluted with CH₂Cl₂-CH₃OH (95:5) mixture. The fractions with compound were collected and evaporated to provide the product as an off white solid in 88.8% (2.80 g) yield. Mp 123-125 °C; HPLC: Retention time 16.5 min; Vydac-C18; (4.6 × 250 mm); linear gradient, water (0.1%TFA) and acetonitrile (0.1 % TFA), 20-50% ACN in 30 min; UV at 230 nm; flowrate, 1 mL/min. ¹H-NMR (CDCl₃) δ 0.89

& 1.32(2s), 1.95(m), 2.15-4.25 (m), 5.21(bd, BocNH), 7.35(m, Ar-H) and 8.31-8.91(m, amide-NH). FAB MS: m/e 759 (M+H).⁺

B. Preparation of trimethyl-10-[L-iso-leucinyl-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate

Trifluoroacetic acid (5 mL) was added to a solution of Trimethyl10-[((N-t-Boc-isoleucinyl)-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate (2.00 g, 2.64 mmol) in CH₂Cl₂ (10 mL) and stirred at room temperature for 30 min. The reaction mixture on evaporation provided a thick paste which on trituration with dry ether gave the product as an off white solid in near quantitative yield. MP 145-147 °C; HPLC: Retention time 5.2 min; Vydac-C18; (4.6 × 250 mm); linear gradient, acetonitrile (0.1 % TFA), water (0.1%TFA) and 20-50% ACN in 30 min: UV at 230 nm; flowrate, lmL/min. ¹H-NMR (D₂O) δ 0.80-1.01 (m), 2.05

(m), 2.89-4.20 (m&s), 7.38 (s, Ar-H). FAB MS: m/e 694 (M+H)⁺. C. Preparation of trimethyl-10-[((N-formyl-L-methionyl-L-leucyl-L-phenylalanyl-L-iosleucinyl)-N-(4-aminophenyl)-acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate To a suspension of trimethyl 10-[L-iso-leucinyl-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7 triacetate (0.50 g, 0.62 mmol), BOP reagent (0.28 g, 0.63 mmol), and N-formyl-Met-Leu-Phe (0.27 g, 0.62 mmol) in dry acetonitrile (10 mL), was added triethylamine (0.32 g, 3.16 mmol) and stirred at room temperature for 5 h under nitrogen atmosphere. The reaction mixture was then treated with water

(10 mL) and evaporated on a rotary evaporator to remove the solvent. The paste thus obtained was loaded as a dichloromethane solution onto a silica gel column and the column was eluted with CH₂Cl₂-CH₃OH (95:5) mixture. The fractions containing the compound were combined and evaporated to afford the product as a light yellowish paste. Yield: 0.40 g (61%); HPLC: Retention time 12.2 min; Vydac- C18; (4.6 × 250 mm); linear gradient, water (0.1%TFA) and acetonitrile (0.1 % TFA), 20-50% AcN in min; UV at 230 nm; flowrate, 1 mL/min. ¹H-NMR (CDCl₃) δ: 0.7-0.9 (m, CH₃), 1.5 and 2.5 (m, CH₂ ), 1-82 (s, SCH₃ ), 3.19-4.0 (m, macrocyclic protons and CH₂), 4.21 and 4.54 (m, CH), 7.21-7.65 (m, Ar-H), 8.05 (s, CHO). FAB MS: m/e 1069 (M+H)⁺.

P. Preparation of 10-[((N-formyl-L-methionyl-L-leucyl-L-phenylalanyl-L-isoleucinyl)-N-(4-aminophenyl)acetamidol-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid

Trimethyl-N-formyl-L-methionyl-L-leucyl-L-phenylalanyl-L-iso-leucinyl)-N-(4-aminophenyl)acetamido]-1,4,7,10-tetra-azacyclododecane-1,4,7-triacetate) (0.35 g, 0.33 mmol) was added to a solution of LiOH (50 mg, 1.2010 mmol) in dioxane-water (3:1) (15 mL). The reaction mixture was stirred at room temperature for 3 h. Water (20 mL) was added to the reaction mixture and the pH of the solution was adjusted to 4.00 by the addition of KHSO₄ solution. The solution was then lyophilized to a solid which was then dissolved in water and subjected to preparative reversed phase (C₁₈) HPLC purification. The fractions containing the title compound with >99% purity were combined and freeze-dried to obtain the product as a colorless fluffy solid. Yield: 112 mg (23.1%); MP 131-143 °C. TLC R_f 0.22 in n-BuOH:AcOH:H₂O (13:2:5) . HPLC: Retention time 16.8 min; Vydac-C18; (4.6 × 250 mm); linear gradient, water (0.1%TFA) and acetonitrile (0.1 % TFA), 20-50% ACN in 30 min; W at 230 nm; flowrate, lmL/min. ¹H-NMR (CD₃OD) δ 0.7-.08 (m, CH₃), 1.5 and 2.4 (m, CH₂), 1.9 (s, SCH₃), 3.19-4.0 (m, macrocyclic protons and CH₂), 4.2 and 4.4 (m, CH), 7.2-7.6 (m, benzene ring), 8.0 (s, CHO). FAB MS: m/e 1027 (M+H)⁺. Anal.: Calcd- for C₄₉H₇₄N₁₀O₁₂S₁ 1.05 CF₃COOH 5.70 H₂O: C, 46.45; H, 6.39; N, 10.14; S, 2.32; F, 9.08, Found: C, 46.54; H, 6.16; N, 10.00; S, 2.52; F, 8.85. (desorption Karl-Fisher). E. Preparation of 10-[ ((N-formyl-1-methionyl-L-leucyl-L-phenylelanyl-L-isoleucinyl)-N-(4-aminophenyl)acetamido]-1,4, 7,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium salt GdCl₃ (3.5 mL of 9.945 mM, 0.0348 mmol) was mixed with 10-[((N-for-L-methionyl-L-leucyl-L-phenylalanyl-L-isoleucinyl)-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (40 mg, 0.0319 mmol). The reaction mixture was heated at 40°C. The pH of the reaction mixture was raised slowly to 7, while the reaction mixture was heated. The product was isolated by semi-preparative HPLC. All fractions containing the product were collected and concentrated under the stream of nitrogen at 40°C. The final solution was lyophilized. Yield 21.3 mg (57%). Elemental Analysis: (Calculated for C₄₉H₇₁N₁₀O₁₂GdS . 4.8 H₂O) : Calcd. C = 46.44, H = 6.40, N = 11.05, and S = 2.53; Found: C = 46.52, H = 6.32, N = 10.97, and S = 2.47. FAB Mass: m/e 1179-1185 (m+H)⁺. Example 9

Synthesis of 10-[((N-formyl-L-methionyl-L-leucyl-L-phenylalanyl-L-aspartyl)-N-(4-aminophenyl)acetamido]-1,4,7 ,10-tetraazacyclododecane-1,4,7-triacetic acid, monogadolinium salt [Gd(for-Met-Leu-Phe-Asp-APA-DO3A]

A. Preparation of Trimethyl-10-[((N-t-Boc-L-β-t-butoxyaspartyl)-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate

To a mixture of β-t-butyl-t-Boc-aspartate (1.00 g, 3.46 mmol), trimethyl 10-[N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate pentahydrochloride (2.73 g, 3.80 mmol) and BOP reagent (1.68 g, 3.80 mmol) in dry acetonitrile (15 mL) was added triethylamine

(1.92 g, 81.97 mmol) and stirred at room temperature under nitrogen atmosphere for 6 h. The reaction mixture was then treated with water (15 mL) and evaporated on a rotary evaporator to remove the solvent to afford a thick paste. The paste was then loaded onto a silica gel column as dichloromethane solution and the column was eluted with CH₂Cl₂-CH₃OH (95:5) mixture. The fractions with compound were collected and evaporated to provide the title compound as an off white soild in 86% (2.40 g) yield. MP 104-107 °C; HPLC: Retention time 12.5 min; Vydac-C18; (4.6 × 250 mm); linear gradient, water (0.1%TFA) and acetonitrile (0.1 % TFA), 20-50% ACN in 30 min; UV at 230 nm; flowrate, lmL/min. ¹H-NMR: (CDCl₃) δ 1.52 (2s, boc group), 2.65-3.52 (m, macrocyclic ring-H and CH₂), 4.55 (m, 1H), 5.87(bd, 1H), 7.45(m, Ar-H) and 8.77 (2s). FAB MS: m/e 808 (M+H).⁺

B. Preparation of Trimethyl-10-[L-aspartyl-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate To a solution of product 9a (2.0 g, 0.15 mmol) in dry CH₂Cl₂ was added dry trifluoroacetic acid and the reaction mixture was stirred at room temperature for 4 h. The reaction mixture, on evaporation under vacuum and trituration of the resulting gum with dry ether, afforded an off white solid (1.96 g, 92%) of the title compound. The product thus obtained was taken to the next step without further purification. MP: 178-181°C; HPLC: Retention time 13.1 min; Vydac-C18; (4.6 × 250 mm); linear gradient, water (0.1%TFA) and acetonitrile (0.1%TFA), 0-50% ACN in 50 min; UV at 230 nm; flowrate, lmL/min. ¹H-NMR (D₂O) : δ 2.38 (m),

2.95-3.38 (m), 3.74 (m) and 7.25-7.48 (m). FAB MS: m/e 652 (M+H) ⁺ . C. Preparation of trimethyl-10-[((N-formyl-L-methionyl -L-leucyl-L-phenylalanyl-L-aspartyl)-N-(4-aminophenyl)acetamidol-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate

A solution of product 9b (0.30 g, 0.46 mmol) in DMF (5 mL) was treated with triethylamine (0.2 g) and then the volume of the solution was reduced under vacuum to ~ 2 mL. In a separate flask N-for-Met-Leu-Phe (0.20 g, 0.45 mmol) was treated with 1,1-carbonyldiimidazole (0.08 g, 0.45 mmol) in dry DMF (5 mL) at room temperature under nitrogen atmosphere for 10 min. To this solution, trimethyl 10-[L-aspartyl-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate in DMF was added and the mixture was stirred at room temperature for 2 h. Water (5 mL) was then added and solvent was removed under vacuum to afford a thick paste of the title compound. For further purification the crude material was loaded onto a silica gel column as CH₂Cl₂ solution and eluted with CH₂Cl₂:CH₃OH (95:5) solvent mixture. The fractions with compound were collected and evaporated to provide the product as a thick colorless paste. Yield: 0.35 g (71%); HPLC: Retention time 15.6 min; Vydac-C18; (4.6 × 250 mm); linear gradient, water (0.1%TFA) and acetonitrile (0.1 % TFA), 20-50% ACN in 30 min; UV at 230 nm; flowrate, lmL/min. ¹H-NMR (CD₃OD) δ 0.75 (2d), 1.42(m), 1.84 (m), 2.38(m), 2.92-3.34 (s & m), 3.74(m)., 4.15-4.73 (4m), 7.25(m), 7.48 (m) and 8.05(s). FAB MS: m/e 1071 (M+H)⁺.

D. Preparation of 10-[((N-formyl-L-methionyl-L-leucyl-L-phenylalanyl-L-aspartyl)-N-(4-aminophenyl)acetamido]-1 ,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid

A solution of trimethyl-10-[((N-formyl-L-methionyl-L-leucyl-L-phenylalanyl-L-aspartyl)-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate (0.30 g, 0.28 mmol) in dioxane (10 mL) was treated with LiOH (0.05 g, 1.2 mmol) in water (2 mL) and stirred at room temperature for 30 min. The pH of the solution was then adjusted to 4.0 with KHSO4. The solution was then diluted to 100 mL with water and loaded onto a reversed phase column, and eluted with 20% acetonitrile-water (0.1% TFA) mixture. The fractions containing the product were collected and lyophilized to afford the product as a colorless fluffy solid. Yield: 0.35 g (71%); MP 138-140° C; TLC: R_f 0.15 in n-BuOH:AcOH:H₂O (13:2:5). HPLC: Retention time 10.7 min; Vydac-C18; (4.6 × 250 mm); linear gradient, water (0.1%TFA) and acetonitrile (0.1 % TFA), 20-50% ACN in 30 min; UV at 230 nm; flowrate, 1 mL/min.¹H-NMR (CD₃0D) δ 0.75 (2d),

1.42 (m), 1.84(m), 2.38(m), 2.92-3.34 (s & m), 3.74(m)., 4.15-4.73 (4m), 7.25(m), 7.48(m) and 8.05(s). FAB MS m/e 1071 (M+H)⁺. Anal.: Calcd. for C₄₇H₆₈N₁₀O₁₄S 1.05 CF₂COOH 5.70 H₂O: C, 54.85; H, 6.66; N, 13.61; S, 3.12; F, 7.88, Found: C, 54.95; H, 6.36; N, 13.41; S, 3.01; F, 7.65. (desorption Karl-Fisher).

E. Preparation of 10-[((N-Formyl-L-methionyl-L-leucyl-L-phenylalanyl-Laspartyl)-N-(4-aminophenyl) acetamidol-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, mono-gadolinium salt

The gadolinium complex was prepared by the method outlined in example 6C . Yield 75%. Anal. Anal. Calcd. for C₄₇H₆₄N₁₀O₁₄GdS 3Na. 7H₂O: C, 42.42; H, 5.91; N, 110.53, Found: C, 6c. Yield 75%. Anal. Anal. 3Na . 7H₂O: C, 42.42; H, 5.91; N, 110.53, Found: C, 41.95; H, 5.31; N, 10.43. FAB MS m/e 1184.3 (M + H)\ Example 10

Synthesis of 10 - [ ( (N-formyl -L-methionyl -L-leucyl -L- phenylalanyl-glycyl -glycyl-glycyl -glycyl ) -N- ( 4-aminophenyl ) - acetamido] -1,4,7 ,10-tetraazacyclododecane-1,4,7-triacetic acid, mono gadolinium salt, [Gd ( for-Met-Leu-Phe-Gly-Gly-Gly- Gly-APA-DO3A) ]

A. Preparation of N-t-Butγloxycarbonyltetraglycine

A solution of tetraglycine (1.0 g, 4.06 mmol) in DMF- water (50 mL, 2:1) was treated with di-t-butylcarbonate

(0.97 g, 4.45 mmol) and triethylamine (1.0 g, 9.88 mmol) and the reaction mixture was stirred at room temperature for 15 h. The pH of the reaction mixture was adjusted to 4 by the addition of 1 N HCl and evaporated to dryness. The solid thus obtained was then washed with chloroform to provide the product in near quantitative yield (1.5 g) as an off white solid. MP 168-171° C; HPLC: Retention time 16.45 min; Vydac-C18; (4.6 × 250 mm); linear gradient, waster (0.1%TFA) and acetonitrile (0.1%TFA), 0-35% ACN in 35 min; UV at 230 nm; flowrate, lmL/min. ¹H-NMR (CD₃OD) d 1. 45 (s), 2 . 81 (s), 3. 84 (s) and 4.14(s). FAB MS: m/e 347 (M+H).⁺ B. Preparation of trimethyl-10-[((N-t-Butyloxycarbonyl- glycyl-gyvcyl-glycyl-glvcyl)-N-(4-aminophenyl)acetamido]- 1,4,7,10-tetraazacyclododecane-1,4,7-triacetate To a mixture of N-t-butyloxycarbonyltetraglycine (1.0 g, 2.89 mmol), trimethyl 10-[N-(4-aminophenyl)acetamido]- 1,4,7,10-tetraazacyclododecane-1,4,7-triacetate

pentahydrochloride (1.71 g, 3.19 mmol), and BOP reagent (1.41 g, 3.18 mmol) in dry DMF (20 mL) was added triethylamine (0.65 g, 6.42 mmol) and stirred at room temperature for 15 h. Ammonium chloride (2 g) in water. (5 mL) was added and stirred for 5 min. After evaporation of the solvent under vacuum, the crude solid obtained was purified on a semi -preparative C18 column with water-acetonitrile (0.1%TFA) as eluant. The fractions with compound were collected and freeze-dried to afford the product as a colorless fluffy solid. Yield: 1.40 g (60%); MP 120-122° C; HPLC: Retention time 20.2 min; Vydac-C18; (4.6 × 250 mm); linear gradient, water (0.1%TFA) and acetonitrile (0.1 % TFA), 20-50% ACN in 30 min; UV at 230 nm; flowrate, lmL/min. ¹H-NMR (CD₃OD) δ 0.76(2d), 1.21(s), 1.43(m),

1.88(m), 2.39(m), 2.92-3.34 (m), 3.72(m)., 4.15-4.73 (3m), 7.15(m). FAB MS: m/e 865 (M+H)!

C. Preparation of trimethyl 10-[glycyl-glvcyl-glycyl-glycyl-N-(4-aminophenyl)-acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate A solution of trimethyl 10-[( ( N-t -Butyloxycarbonyl -glycyl-glycyl-glycyl-glycyl)-Ν-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate (1.40 g, 1.62 mmol) in methanol (10 mL) was treated with methanol saturated with HCl (5 mL) and stirred at room temperature for 10 min. After evaporation of the solvent on a rotary evaporator, the paste obtained was triturated with ether to provide the title compound as an off white solid in a near quantitative yield (1.40 g); Mp 145-148° C; HPLC: Retention time 6.28 min; Vydac-C18; (4.6 × 250 mm); linear gradient, water (0.1%TFA) and acetonitrile (0.1 % TFA), 20-50% ACΝ in 30 min; UV at 230 nm; flowrate, lmL/min. ¹H-ΝMR (CD₃OD) δ

0.76(2d), 1.45(m), 1.89(m), 2.42(m), 2.72-3.54 (m), 3.82(m)., 4.15-4.73 (3m), 7.15(m). FAB MS : m/e 765 (M+H).⁺ D. Preparation of trimethyl-10-[N((N-formyl-L-methionyl-L-leucyl-L-phenylalanyl-glycyl-glycyl-glycyl-glycyl)-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraaza¬cyclododecane-1,4,7-triacetate

To a mixture of trimethyl 10-[glycyl-glycyl-glycyl-glycyl-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate (1.0 g, 1.31 mmol), N-formyl-Met-Leu-Phe (0.63 g, 1.44 mmol) and BOP reagent (0.64 g, 1.44 mmol) in dry DMF (15 mL) was added triethylamine (0.30 g, 2.96 mmol) and stirred at room temperature for 15 min under nitrogen atmosphere. Ammonium chloride (2 g) in water (5 mL) was added and stirred for 5 min. After evaporation of the solvent under vacuum, the crude solid obtained was purified on semi-preparative C18 column with water-acetonitrile (0.1%TFA) as eluant. The fractions with the product were collected and freeze-dried. Yield: 0.62 g (40%); MP 118-121° C; HPLC: Retention time 14.21 min; Vydac-C18; (4.6 × 250 mm); linear gradient, water (0. 1%TFA) and acetonitrile (0.1 % TFA), 20-50% ACN in 30 min; UV at 230 nm; flowrate, lmL/min. ¹H-NMR (CD₃OD) δ 0.75(2d), 1.43(m), 1.82(m),

2.39(m), 2.62-3.44 (m), 3.62 (m)., 4.15-4.73 ( 3m), 7.15(m), 7.48(m) and 8.04(s). FAB MS : m/e 1184.5 (M+H).⁺

E. Preparation of 10-[((N-Formyl-L-methionyl-L-leucyl-L-phenylalanyl-glycyl-glycyl-glycyl-glvcyl)-N-(4-aminophenyl)acetamidol-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid

To a solution of trimethyl 10-[((N-Formyl-L-methionyl-L-leucyl-L-phenylalanyl-glycyl-glycyl-glycyl-glycyl)-N-(4-aminophenyl)acetamido]-1,4,7,10-tetraazacyclododecane~-1,4,7-triacetate (0.60 g, 0.51 mmol) in dioxane-water (50 mL; 3:1) was added LiOH (85 mg, 2.02 mmol) and stirred at room temperature. After 60 min the reaction mixture was treated with 1 N HCl to pH 4.0 and diluted with water to 200 mL . The solution was then pumped onto a semi-prep HPLC column and eluted with water-acetonitrile (0.1%TFA). The fractions with compound were collected and freeze-dried to provide the product as colorless fluffy solid. Yield: 0.25 g

(51%); MP 140-143°C; TLC: R_f 0.15 in n-BuOH:AcOH :H₂O (13:2:5). HPLC: Retention time 9.09 min; Vydac-C18; (4.6 ×

250 mm); linear gradient, water (0.1%TFA) and acetonitrile

(0.1 % TFA), 20-50% ACN in 30 min; UV at 230 nm; flowrate, lmL/min. ¹H-NMR (CD₃OD) δ 0.79{2d), 1.41(m), 1.84 (m),

2.38(m), 2.93-3.34(s & m), 3.74(m), 4.10-4.72 (4m), 7.24(m), 7.47(m) and 8.07s). m/e 1142.4 (M+H)⁺. Anal.: Calcd. for C₅₁H₇₅N₁₃O₁₅S 2.08 CF₃COOH 0.61 H₂O: C, 47.68; H, 5.61; N, 13.11; S, 2.31; F, 8.53, Found: C, 47.68; H, 5.65; N, 13.04; S, 1.99; F, 8.52. (desorption Karl-Fisher). F. Preparation of 10-[((N-formyl-L-methionyl-L-leucyl -L-phenylalanyl-glvcyl-glycyl-glycyl-glycyl)-N-(4-amino¬phenyl) acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid gadolinium salt GdCl₃ (0.93 mL of a 49.7 mM solution, 0.0462 mmol) was mixed with 10-[((N-formyl-L-methionyl-L-leucyl-L-phenyl-alanyl-glycyl-glycyl-glycyl-glycyl)-N-(4-aminophenyl) acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid as triethylammonium salt (64.82 mg, 0.04665 mmol) in water. The reaction mixture was heated at 50°C. The pH of the reaction mixture was raised slowly to 7, while the reaction mixture was heated. When the pH of the reaction mixture reached 7, the sample was allowed to cool, and the product was purified by semi-preparative HPLC method. All fractions containing the product were collected and concentrated under the stream of nitrogen at 40°C. The final solution was lyophilized. Yield 50 mg (39%). Elemental Analysis: (Calculated for C₅₁H₇₂N₁₃O₁₅GdS . 6.0 H₂O) : Calcd. C= 43.57, H = 6.03, N = 12.95, and S = 2.28; Found: C = 43.69, H = 5.95, N = 12.83, and S = 2.14. FAB Mass: m/e at 1294.4 - - > 1300 (m+H)⁺ with gadolinium pattern. Example 11

Synthesis of 10-[((L-methionyl-L-leucyl-L-phenyl-alanyl-glycyl-glycyl-glycyl-glycyl)-N-(4-aminophenyl) acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, mono gadolinium salt, [Gd(Met-Leu-Phe-Gly-Gly-Gly-Gly-APA-DO3A]

A. Preparation of 10-[ ((L-methionyl-L-leucyl-L-phenyl-alanyl-glycyl-glycyl-glycyl-glycyl)-N-(4-aminophenyl)-acetamidol-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid

A solution of N-formyl-Met-Leu-Phe-Gly-Gly-Gly-Gly-APA-DO3A (from example 10d, 0.45 g, 0.08 mmol) in methanol was treated with 2 N HCl and stirred at 40° C for 4h and the progress of the reaction was monitored by an HPLC method as the disappearance of the starting material. The pH of the reaction mixture was adjusted to 5 with sodium carbonate solution. The sample was purified by the HPLC method. The fractions were collected and lyophilized to a white fluffy solid, Yield 0.20 g (51%). Analytical data: Yield: 0.20 g (51%); MP124-126º C; TLC: R_f 0.10 in n-BuOH : AcOH:H₂O

(13:2:5). HPLC Retention time 5.76 min; Vydac-C18; (4.6×

250 mm); linear gradient, water (0.1% TFA) and acetonitrile (0.1% TFA), 20-50% ACN in 30 min; UV at 230 nm; flow rate, lmL/min.¹H NMR (CD₃OD) δ 0.90(2d), 1.42 (m), 1.84 (m),

2.40(m), 2.82-3.34(s & m), 3.74(m)., 4.10-4.72 (4m), 7.25(m), 7.44(m) . MS M/z 1114.2 (M+H)⁺. Anal. Calcd. for C₅₀H₇₄N₁₃O₁₄S 2.06 CF₃COOH 0.51 H₂O: C, 47.57; H, 5.51; N, 13.22; S, 2.45; F, 8.68. Found: C, 47.68; H, 5.39; N, 13.41; S, 2.21; F, 8.49. (desorption Karl-Fisher). B. Synthesis of 10-[ ((L-methionyl-L-leucyl-L-Phenyl-alanyl-glycyl-glycyl-glycyl-glycyl)-N-(4-aminophenyl)-acetamidol-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, mono gadolinium salt

GdCl₃ (0.65 mL of a 49.7 mM solution, 0.0323 mmol) was mixed with 10-[((N-L-methionyl-L-leucyl-L-phenylalanyl-glycyl-glycyl-glycyl-glycyl)-N-(4-aminophenyl)-acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (43.3 mg, 0.0319 mmol) in water. The reaction mixture was heated at 50°C for several hours. The pH of the reaction mixture was raised slowly to 7.5, while the reaction mixture was heated. When the pH of the reaction mixture reached 7.5, the sample was allowed to cool, and the product was purified by a semi-preparative HPLC method. All fractions containing the product were collected and concentrated under the stream of nitrogen at 40°C. The final solution was lyophilized. Yield 30 mg (73%). Elemental Analysis: (Calculated for C₅₀H₇₁N₁₃O₁₅GdS. 11 H₂O) : Calcd. C= 40.97, H = 6.44, N = 12.27, and S = 2.17; Found: C = 41.07, H = 5.45, N = 11.65, and S = 1.94. FAB Mass: m/e at 1267 - ->1271 (m+H)⁺ with gadolinium pattern.

Example 12

Synthesis of 10-[((t-Boc-methionyl-L-leucyl-L-phenylalanyl-glycyl-glycyl-glycyl-glycyl)-N-(4-aminophenyl)-acet¬amido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid- mono gadolinium salt, [Gd(t-Boc-Met-Leu-Phe-Gly-Gly-Gly-Gly-APA-DO3A)]

A. Preparation of 10-[((t-Boc-methionyl-L-leucyl-L-phenylalanyl-glycyl-glycyl-glycyl-glycyl)-N-(4-aminophenyl)-acetamidol-1,4,7.10-tetraazacyclododecane-1,4,7 triacetic acid

To a solution of Met-Leu-Phe-Gly-Gly-Gly-Gly (0.2 g, 0.04 mmol) in DMF/water (2:1, 10 mL) was added di-t-butyldicarbonate and triethylamine and stirred at room temperature for 15 min. The reaction mixture was then treated with 1.0 N HCl to adjust the pH to 4.0. The reaction mixture was purified by an HPLC and all fractions were collected, lyophilized to a solid fluffy solid. Yield, 0.18 g (58%). Analytical data: Yield: 0.18 g (58%); MP 148-151 °C; TLC: R_f 0.25 in n-BuOH:AcOH:H₂O (13:2:5). HPLC:

Retention time 19.45 min; Vydac-C18; (4.6 × 250 mm); linear gradient, water (0.1%TFA) and acetonitrile (0.1%TFA), 20-50% ACN in 30 min; UV at 230 nm; flowrate, lmL/min.¹H NMR (CD₃OD) δ 0.78(2d), 0.98(s), 1.46(m), 1.85(m), 2.38(m),

2.94-3.38(s & m), 3.78(m), 4.10-4.74 (4m), 7.29(m), 7.49(m) and 8.07(s). MS (FAB) m/z 1214.5 (M+H)⁺. Anal. Calcd. for C₅₅H₈₂N₁₃O₁₆S 2.09CF₃COOH 1.26H₂O: C, 48.21; H, 5.92; N, 12.35; S, 2.17; F, 8.08, Found: C, 48.21; H, 5.79; N, 12.05; S, 2.41; F, 8.09. (desorption Karl-Fisher).

B. Synthesis of 10-[((t-Boc-methionyl-L-leucyl-L-phenylalanyl-glycyl-glycyl-glycyl-glycyl)-N-(4-aminophenyl) -acetamidol-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, mono gadolinium salt.

GdCl₃ (0.74 mL of a 49.7 mM solution, 0.0367 mmol) was mixed with 10-[((t-Boc-methionyl-L-leucyl-L-phenylalanylglycyl-glycyl-glycyl-glycyl)-N-(4-aminophenyl)-acetamido]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (53.10 mg, 0.0367 mmol) in 3.0 mL water. The reaction mixture was heated at 50°C. The pH of the reaction mixture was raised slowly to 7, while the reaction mixture was heated. When the pH of the reaction mixture reached 7, the sample was allowed to cool, and the product was purified by a semi-preparative HPLC method. All fractions containing the product were collected and concentrated under the stream of nitrogen at 40°C. The final solution was lyophilized. Yield (62 mg, 95%) Elemental Analysis: (Calculated for C₅₅H₇₈N₁₃O₁₆GdS. 8.5 H₂O) : Calcd. C= 43.47, H = 6.05, N = 11.98, and S = 2.11; Found: C = 43.52, H = 6.05, N = 11.63, and S = 2 . 05 . FAB Mass : m/e at 1366 . 3 - - >1371 (m+H ) ⁺ with gadolinium pattern.

Example 13

Synthesis of 10-[ ( (N-formyl-L-norleucyl--L-Leucyl-L-phenylalanine-L-Norleucine-L-tyrosyl)-L-lysine-N-N-(4-aminophenyl)acetamidol-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, mono gadolinium salt [Gd(for-Nle-Leu-Phe-Nle-Tyr-Lys-PPA-DO3A)]

A. Preparation of p-N-chloroacetylphenylacetic acid p-Aminophenylacetic acid (3.0 g, 20 mmol) was dissolved in dimethylacetamide (40 ml) and cooled to 0°C. Chloroacetyl chloride (3.1 g, 28 mmol) was added dropwise with vigorous stirring. The reaction mixture then was stirred at room temperature for 1 h. The reaction mixture was evaporated to dryness and water (30 ml) was added to the residue with vigorous stirring. After filtration, the crude product of the title compound (4.5 g) was obtained. For further purification it was recrystallized from 65% of EtOH to provide the product (2.83 g, yield 62%). MP 14130 142° C; HPLC: Retention time 9.75 min; Vydac-C18; (4.6 × 250 mm); isocratic, water (0.1%TFA) and acetonitrile (0.1 % TFA), 15% ACN; UV at 230 nm; flowrate lmL/min. ¹H-NMR (DMDO-d₆) δ 2.91

& 4.28(s) and 7.18-7.45 (m). FAB MS : m/e :228 (M+H)⁺ and 245 (M+NH₄)⁺. B. Preparation of tri-t.butyl-10-[(4-carboxymethylphenyl)acetamidol-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate

Tri-t-butyl-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate hydrochloride (3.3 g, 5.5 mmol) and K₂CO₃ (3 g) were added in dimethylacetamide (25 ml). p-n-chloroacetylphenylacetic acid (1.1 g, 5 mmol) in dimethylacetamide (10 ml) was added and the reaction mixture was stirred at 45° C for 29 h. The reaction mixture was filtered and evaporated to dryness. The residue was purified by preparative HPLC to obtain the product (1.64 g, yield 46.5 %). MP 138-140° C; HPLC: Retention time 5.18 min; Vydac-C18; (4.6 x 250 mm); isocratic, water (0.1%TFA) and acetonitrile (0.1% TFA), 40% ACN; UV at 230 nm; flowrate lmL/min. ¹H-NMR (DMDO-d₆) δ 1.32(m), 2.71-4.02 (m), 7.31-7.81(m) and 9.01(s). FAB MS : m/e 706 (M+H)⁺.

C. Preparation of N(γ)-[[-4-[[[1,4,7-tris(t-butoxycarboxymethyl)-1,4,7,10-tetraazacyclododecan-10-yl]acetyl]-amino]phenyl]acetyl]-N-formyl-L-norleucyl-L-leucyl-L-phenyl-alanyl-L-morleucyl-L-tyrosyl)-L-lysine

Tri-t-butyl 10-[(4-carboxymethylphenyl)acetamido]-1,4, 7,10-tetraazacyclododecane-1,4,7-triacetate (105 mg, 60% purity) and carbonyldiimidazole (16.2 mg, 0.1 mmol) were mixed in DMF 0.5 ml and stirred for 10 min under nitrogen atmosphere. N-formyl-Nle-Leu-Phe-Nle-Tyr-Lys (61.8 mg, 0.075 mmol) mixed with Et₃N (1:1 ratio) in DMF (1 ml) was added. The reaction mixture was then stirred at room temperature for 22 h under nitrogen atmosphere. The reaction mixture was evaporated to dryness. Water (10 ml) was added with vigorous stir. The insoluble product was isolated by filtration, washed and dried. Yield: 79.8 mg (70%). MP 168-171°C; HPLC: Retention time 14.2 min; Vydac-C18; (4.6 × 250 mm); isocratic, water (0.1%TFA) and acetonitrile (0.1%TFA), 40% ACN; UV at 230 nm; flowrate 1 mL/min. ¹H-NMR (DMDO-d₆) δ

0.70-1.84(m), 2.38(m), 2.92-3.58 (m), 3.74(m), 4.10-4.72(m) and 8.10(s). FAB MS: m/e 1510.2 (M-H)-, 1511.6 (M+H)⁺ and 1533.6 (M+Na)⁺.

D. Preparation of N(γ)-[[-4-[[[1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-10-yl]acetyl]amino]phenyl]acetyl]-N-(N-formyl-L-norleucyl-L-leucyl-L-phenylalanyl-L-norleucyl-L-tyrosyl)-L-lysine

To a solution of N(γ)-[[-4-[[[1,4,7-tris(t-butoxy¬carboxymethyl)-1,4,7,10-tetraazacyclododecane-10-yl]acetyl]amino]phenyl]acetyl]-N-(N-formyl-L-norleucyl-L-leucyl-L-phen ylalanyl-L-norleucyl-L-25-tyrosyl)-L-lysine (133 mg, 0.088 mmol) in trifluoroacetic acid (0.5 mL) was added anisole

(31.3 mg, 0.29 mmol) and stirred at room temperature for 24 h. After evaporation of the solvent under vacuum, the residue was dissolved in 50% acetonitrile-water (250 30 mL) and purified by reversed phase preparative HPLC. The fractions containing product were combined and lyophilized to obtain the title compound as a white fluffy solid. Yield: 36.8 mg (31.2%). MP 159-162° C; HPLC: Retention time 4.61 min; Vydac C18, 4.6 × 250 mm; 40% acetonitrile (0.1% TFA) in H₂O (0.1% TFA) (pH 2.0); UV at 230 nm; flowrate, 1 ml/min.

¹H-NMR (D₂O) : δ 0.83-0.89 (CH₃), 3.11-3.46 (macrocyclic protons), 1.32-1.68 (CH₂), 7.24-7.51 (benzene ring), 8.15

(CHO) . FAB MS: m/e 672.6 (M+2H)²⁺ and 1343.4 (M+H)⁺. : Anal. Calcd. for C₆₇H₉₇N₁₂O₁₇ 1.27 H₂O ·1.97 TFA: C, 53.59; H, 6.43; N, 10.57. Found: C, 53.14; H, 6.37; N, 10.43; H₂O 1.44%, TFA 14.13% (desorption KarlFisher) .

E. Preparation of N(γ)-[[-4-[[[1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecan-10-yl]-acetyl]amino]- phenyl]-acetyl]-N-(N-formyl-L-norleucyl-L-leucyl-L-phenylalanyl-L-norleucyl-L-tyrosyl)-L-lysine gadolinium salt GdCl₃ (0.67 mL of a 49.7 mM solution, 0.0334 mmol) was mixed with N(γ)-[[-4-[[[1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecan-10-yl]acetyl]amino]phenyl]acetyl]-N-(N-forrrryl-L-norleucyl-L-leucyl-L-phenylalanyl-L-norleucyl-L-tyrosyl)-L-lysine (53.11 mg, 0.0334 mmol) in water. The reaction mixture was heated at 40°C. The pH of the reaction mixture was raised slowly to 7, while the reaction mixture was heated. When the pH of the reaction mixture reached 7, the sample was allowed to cool, and the product was purified by a semi-preparative HPLC method. All fractions containing the product were collected and concentrated under the stream of nitrogen at 40°C. The final solution was lyophilized. Yield 28 mg (54%). Elemental Analysis: (Calculated for C₆₇H₉₄N₁₂O₁₇Gd. 11.3 H₂O) : Calcd. C= 47.31, H = 6.91, N = 9.98; Found: C = 47.75, H = 6.57, N = 9.41. FAB Mass: m/e at 1495.4-->1502 (m+H)⁺with gadolinium pattern.

Example 14

A. Binding Affinity ( K_d) of Native and Gd-Labeled Chemotactic Peptides

Competition binding experiments were performed with rabbit polymorphonuclear leukocytes (PMNs) isolated from peritoneal exudate. Isolated PMNs were diluted to 1 × 10⁷ cells/mL in assay buffer, which was varied initially in an effort to identify conditions that optimized total binding. The assay buffer contained 15 mM Hepes, pH 7.3, 148 mM NaCl, 0.15 mM CaCl₂, and 0.1% BSA (fatty acid free). Because of the low solubility of native and Gd-(IPA-DO3A)-fnLLFnLYK, these two peptides were solubilized in buffer containing 1.5% BSA. The radioligand standard fML³HF was diluted in the standardized assay buffer and 25 mL was placed into polypropylene tubes containing test chemotactic peptide (25 mL) at dilutions of 10^-13 M to 10^-3 M, depending on published dissociation constants of the various test peptides. Tubes containing the peptide mixture were placed in a 15°C water bath and allowed to equilibrate. To each tube, 100 mL of PMNs (1 × 10⁶) were added to initiate the reaction. After 45 min at 15°C, the reaction was terminated with the addition of 3 mL ice-cold assay buffer. Cells were collected by vacuum filtration over GF/C filters. Filters were washed 2x with 3 mL each of assay buffer and were then placed in Eco-Scint for liquid scintillation counting. Specific binding (%) was calculated as:

(sample cpm - cpm of lowest binding sample) × 100

(cpm of highest binding sample - cpm of lowest binding sample)

Data were subjected to 'Ligand' analysis to determine the K_d (1/K_a) of competing peptides relative to the K_d of fMLF. Figure 1 shows the results for five native chemotatic peptides - fMLF, fnLLF, fMLFK, fnLLFnLYKDDD and fnLLFnLYK (open symbols) - and five Gd-labeled derivatives (closed symbols) .As shown in Fig 1.both Gd- labeled and unlabeled chemotactic peptides compete with fML³HF.

Table 1. Comparison of Kd and Ka from competition of Gd-labeled or unlabeled chemotactic peptides with fML³HF

The peptides fall into two groups with the native peptide fMLF having the highest binding affinity of the main group and with a minor group of low binding affinity consisting of two gadolinium peptides, Gd-fMLF and Gd-fnLLF. The binding affinities obtained with the 'Ligand' program are summarized in Table I.

B. Dependence of Binding Affinity with the Chain Length of the Peptide

Table 1 also shows that chelation produced a much greater reduction in the binding affinity of the tripeptides than in the tetrapeptides. In particular, Gd-(IPA-DO3A)-fMLFK has a binding affinity that is of the same order of magnitude as fMLF. This is shown graphically, in Fig. 2 below, where the log₁₀ of the association constant (K_a) is plotted against the Gd - formyl interatomic distance, determined from computer-generated molecular models (Hyperchem). The 'native' peptides are also shown on this graph, with their position on the x-axis determined by the Gd-formyl interatomic distance of their Gd-APA-DO3A derivatives. Logio K_a as a function of Gd-formyl interatomic distance is shown in Fig. 2.

This graph (Fig. 2) shows that binding strength (of the Gd-peptides to PMNs) increases as the distance between the gadolinium chelate and formyl group (based on extended linear arrangement) of the chemotactic peptide also increases. By comparison, the native peptides show a less distinct trend of binding vs length. The binding of Gd(IPA-DO3A)-f-MLFK is greater than its native peptide. The reason for this increase is not clear at this stage, but it may be due to the conversion of the ionizable amine of lysine to a non-charged (and more lipophilic) phenylthiourea moiety. In any case, the magnitude of the affect is not large relative to the differences between tri- and tetrapeptides for example.

Example 15

A. Real-Time Video Analysis of PMN Chemotaxis in Response to fMLF and Gd(IPA-DO3A)-f-MLFK Ideally, a Gd-chelated chemotactic peptide should serve as an antagonist for the receptor, since avoiding activation would conserve PMNs labeled in the blood for extravassation and chemokinesis to the site of infection. We determined the degree of orientation of various species' PMNs to the peptides using the Zigmond Chamber and real¬time video microscopy. Exudate PMNs or human peripheral PMNs from a ~100μL finger prick were placed onto a glass coverslip and incubated at 37.5°C, under a 5% CO₂ atmosphere for 20 min to allow the PMNs to adhere to the glass. The coverslip was washed in the case of the whole blood samples and then placed cell side down over the bridge and wells of the Zigmond chamber. A peptide at a given concentration in incubation buffer (1% gelatin in Hanks balanced salt solution buffered with 10 mM of HEPES) was placed in one of the two wells on either side of the bridge, and incubation buffer was added to the second well. Cell orientation in the resulting gradient was scored 20 min after filling the wells. Chemotaxis was determined by percent of total PMNs counted orienting towards the chamber containing the peptide.

Table 3. Orientation of PMNs in gradients of various chemotactic peptides

The data (Table 3) confirm that the native peptide fMLF is an agonist and that the Gd-labeled derivatives Gd-fnLLFnLYK and Gd-fMLFK are also agonists. As the concentration at which PMNs maximally orient in the Zigmond chamber corresponds to the approximate K_d of the receptors on the PMNs for the particular peptide, the Zigmond chamber results also confirm the Kds of the native and Gd-labeled peptides as determined from competitive binding studies. These data represent the first demonstrations of known PMN chemotaxis in response to a Gd-chelated peptide.

These data also demonstrate the differences in binding affinities of formyl peptide receptors on PMNs from human, rabbit, mouse, and rats. The receptors on mouse PMNs have an approximate K_d of 10^-6 M for fMLF which is in agreement with results published by Sasagawa et al. ( Immunopharmacol Immunotoxicol. 1992. 14:625-635). Human and rabbit PMN receptors have Kd values of ~10^-9 M, three orders of magnitude lower than found with mouse PMNs.

Example 16

A. Tn Vitro MRI Experiments with Gd(IPA-DO3A)- fnLLFnlKY, Gd(IPA-DO3A)-fMLFK. and ProHance® We performed test tube MRI experiments using rabbit peritoneal PMNs. ProHance® (Gadoteridol, HP-DO3A), as a non-protein Gd- control, and a blank that contained no PMNs, were used as control.

"Test tube" MRI experiments used rabbit peritoneal PMNs rather than rat peripheral blood PMNs, (to avoid inclusion of platelets and other types of leukocytes). ProHance was included as a non-protein Gd-control and a negative control which contained no PMNs in order to detect images produced by gelled/precipitated Gd-peptide was also included. A careful analysis of the distribution of material between the cells and the supernatant was also performed. Since receptor binding experiments showed that PMNs could bind the fML HF in the presence of 1.5% BSA, the current series of test (bullet) tube experiments for both Gd-(IPA-DO3A)-fnLLFnLYK and Gd-(IPA-DO3A)-fMLFK were carried out with 1.5% BSA in the assay buffer.

The quantity of radiolabeled and unlabeled Gd-peptide was calculated to achieve the desired concentrations in 1 mL final volume containing the peptide, cells, and buffer. Binding experiment may be carried out at room temperature for 30 min on a rocker plate. Cells were collected by centrifugation at 500 xg for 2 min. The test tubes were placed into the magnet and the pellet was imaged. The supernatant liquid was removed and cells were washed twice with buffer and the pellet imaged again. The total Gd- peptide concentration in the pellet and washes was determined by the addition of tracer quantities of Gd- peptide. The specific activity in cpm/mmole was known for each experimental sample. The signal intensity of both the supernatant and final pellet was determined using the same voxel size in all experiments. Initial signal intensity of the supernatant was measured at the tapered end of the tube above the pellet (since the image slice is 5 mm) in the first image. Final pellet signal intensity was determined from the last MRI after all wash steps. PMN competence varied with each cell preparation and this variability impacted heavily on the results test tube experiments were initiated only when specific binding as measured using fML HF was 5-8% after 5 min reaction time. The experimental details and results of imaging studies for Gd-(IPA-DO3A)-fnLLFnLYK, Gd-(IPA-DO3A)-fMLFK, and ProHance are shown in Tables 4, 5, 6.

Table 4. MRI test tube experiment of Gd-(IPA-DO3A)-fnLLFnLYK dissolved in the standard assay buffer containing 1.5% BSA.

Table 5. MRI bullet tube experiment of Gd-fMLFK dissolved in the standard assay buffer containing 1.5% BSA.

Table 6. MRI test tube experiment of ProHance dissolved in the standard assay buffer containing 1.5% BSA.

B. Signal intensity of cell pellets as a function of pellet concentration.

The signal intensity of the pellet as a function of the pellet concentration of gadolinium complex appears to reach a maximum of about 4 (Fig. 3). The two peptides, Gd(IPA-DO3A)-fnLLFnLYK and Gd(IPA-DO3A)-fMLFY are similar and have up to 4 times the signal for the same concentration of ProHance This is presumably a function of the different relaxivities of these two classes of compounds. The similar relationship between the signal intensity and the pellet concentration of the two peptides suggests that they are in the same environment As we believe that the Gd- (IPA-DO3A) -fMLFK is soluble at all concentrations tested we believe that the Gd-(IPA-DO3A)- fnLLFnLYK present in the pellet is as internalised material rather than as a precipitate physically entrapped within the cell pellet. We have washed these cell pellets and found that 67% of the material cannot be washed off the cells whereas for inulin 96% can be washed off. The signal intensity of the pellet after incubation with Gd-peptides is higher than that of ProHance at the same concentration is shown in Fig 3.

Gd-(IPA-DO3A)-fnLLFnLYK produced an imageable pellet with an initial concentration of 15mM, (SI = 3.9 times background) whereas to obtain the same relative signal intensity with Gd-(IPA-DO3A)-fMLFK the initial concentration required was 300μM. The highest signal intensity with ProHance was 1.6 at an initial concentration of 1050 mM (this signal intensity was achieved with 1 mM Gd-fnLLFnLYK).

Example 17

A. Association of Gd-(IPA-DO3A)-fnLLFnLYK with Cells Association of Gd-(IPA-DO3A)-fnLLFnLYK and PMNs should provide insight into the mechanism of uptake and allow us to assess if uptake is receptor mediated or if nonspecific interactions lead to nonspecific associations with the PMN surface. The experiment (given below) is in agreement that Gd(IPA-DO3A)-fnLLFnLYK in rabbit PMNs internalized as compared to Gd(IPA-DO3A)-f-MLFK Association (molecules/cell) of Gd(IPA-DO3A)-fnLLFnLYK and Gd(IPA-DO3A)-f-MLFK with rabbit peritoneal PMNs is shown in Fig.4.

For the total binding comparison, 2 aliquots of rabbit PMNs were suspended in 5 ml HBSS 0.1% BSA, fatty acid free, to yield ~3.8 × 10⁹ PMNs/aliqot. Both peptides were added to yield a final concentration of 209 nM. Peptides were reacted with the cells for 30 min at room temperature. Cells were collected by centrifugation, washed twice with HBSS, and the radioactivity associated with the pellet was measured in a gamma counter. The radioactivity associated with the cells at the end of the study was 8.65% for the Gd(IPA-DO3A)-fnLLFnLYK and 0.33% for the Gd(IPA-DO3A)-f-MLFK.

Approximately 6 times more Gd(IPA-DO3A)-fnLLFnLYK (hexa) is associated with the PMNs than Gd(IPA-DO3A)-f-MLFK

(tetra). These data support the results of test tube MRI experiments where a higher signal intensity was obtained at with Gd(IPA-DO3A)-fnLLFnLYK at lower initial incubation concentrations (i. e . 15 mM) and a greater amount of Gd ( IPA-DO3A) -fnLLFnLYK vs . Gd ( IPA-DO3A) -f -MLFK was associated with the PMN pellet at all concentrations of Gd- ( IPA-DO3A) - fnLLFnLYK tested .

Example 18

Comparison of the biodistribution of Gd-153 (for-Nle-Leu-Phe-Nle -Tyr- ( N ( g ) ) Lys - I PA-DO3A ) with that o f an extravascular tracer

The left rectus muscle of nine male Sprague-Dawley rats (250-350 g) were inoculated with human E. Coli (10⁹) 20 hours prior to the study. The rats were anaesthetized with sodium pentobarbital, and 5 mCi (3.8 × 10 moles) of Gd-153 (for-Nle-Leu-Phe-Nle-Tyr-(N(g))Lys-APA-DO3A) was co-injected i.v.with approximately 9 mCi of ^99mTc-DTPA. The animals were sacrificed at 1, 2 and 4 hours post injections (3 animals per time point). Specific organs were removed from each animal and assayed for Tc-99m. Five days post sacrifice (to allow for decay of Tc-99m) the tissues were assayed for Gd-153 The results demonstrated that the ratio of the Gd-peptide m the infected muscle relative to the noninfected muscle exceeds that of Tc-99m-DTPA by two hours after injection. This is significant since it shows that the uptake of the Gd-peptide m the infection site exceeds the uptake expected on the basis of increased vascular permeability.

Example 19

Comparison of the biodistribution of Gd-153 (for-Nle-Leu-Phe-Nle-Tyr-(N(g)) Lys-APA-DO3A) with Tc-99m-labeled white blood cells (WBCs)

A biodistribution study performed in both normal and infected rats (male, Sprague dawley, 85 -100 g) with Gd(IPA-DO3A)-fnLLFnLYK showed that the %ID increased with time up to 0.16% at 6 h post injection. This is about 4 times the amount of Gd(IPA-DO3A)-fnLLFnLYK found in the normal leg and 2 times the amount of ^99mTc-DTPA in the same infected leg. Uptake of ^99mTc-DTPA and Gd-fnLLFnLYK in infected and noninfected muscle is shown in Fig.5. Example 20

Relaxivity Measurements of Gd (for-Nle-Leu-Phe-Nle-Tyr-(N(g))Lys-APA-DO3A).

The relaxivity measurements were carried out by measuring T_1s of several solution of different concentrations of Gd(IPA-DO3A)-f-nLLFnLYK at 20 MHz and at 37°C. The experiments were carried out in different media, e.g., bis-tris buffer, human plasma, rat plasma, and rat whole blood. In all cases, the pH of the medium was adjusted to 7.4 with bis-tris buffer and ionic strength at 0.1. In the case of rat plasma experiment, two types of experiments were carried out. In the first experiment, the plasma was first separated from whole blood, samples of Gd(IPA-DO3A)-fnLLFnLYK with different concentration were prepared, and T_xs were measured. In the second experiment, the sample was prepared in whole blood, plasma was separated, concentration was determined from the knowledge of counts and specific activity of the stock solution, and T₁ was measured. Both experiments gave similar results. The slope of the plot of 1/T₁ vs. concentration gave a measure of relaxivity. Data are given in Table 7.

Since it was demonstrated that Gd(IPA-DO3A)-fnLLFnLYK binds with WBCs, we determined the relaxivity of the conjugate, Gd(IPA-DO3A)-fnLLFnLYK, in the presence of WBCs. The following procedure was used: Whole blood from 6 rats (42 mL) was collected and white blood cells were separated and suspended in 0.21 mL isotonic saline. The sample of Gd(IPA-DO3A)-fnLLFnLYK was added to it, the final volume was made up to 0.5 mL, and the T₁ was measured. The sample was diluted with isotonic saline to give different concentrations in the mixture and T₁ were measured. The samples were counted for the radioactivity which was used to calculate the concentration of the conjugate. The observed T₁s were due to the bound and unbound conjugate. A linear regression analysis of the data gave a relaxivity value of 10.75 mM^-1s^-1. Since the relaxivity of unbound conjugate, Gd(IPA-DO3A)-fnLLFnLYK, is known from the previous experiments, one can calculate the values of the ratio of bound to unbound conjugate and the relaxivity of the conjugate bound to white cells. The calculated relaxivity value is given in Table 7. Table 7. Relaxivity Values of Gd(IPA-DO3A)-f-nLLFnLYK at 20 MHz and 37ºC.

Example 21

Preparation of Pluronic® F108 dichloride.

In a filtered solution of 21 g (3 mEq) of Pluronic® F108 (BASF) in 80 ml of CCI₄, there were added at room temperature 1 ml (4.2 mEq) of tributylamine. After cooling, 2.2 ml (30 mmol) of thionyl chloride were added and the mixture was refluxed 4 hrs, whereby it turned red. It was filtered, stripped from the solvents, the residue redissolved in 80 ml of CCl4 around 60°C and 200 ml of ether were added which caused the precipitation of 20.3 g of solid; the latter was dissolved in AcOEt (80 ml) bleached with active charcoal, filtered and allowed to crystallize after the addition of 200 ml of ether. There were collected 19.06 g of the desired F108 dichloride. The reaction is schematized below.

Example 22

Two g (0.28 mEq) of the F108 dichloride from Example 21 were dissolved in 8 ml of dry DMF and there were added 0.54 g (2.9 mmol) of potassium phthalimide. The mixture was stirred overnight at 90°C after which it was cooled and filtered over celite. The solution was heated to 50°C, 30 ml of ether were added and, upon cooling, a solid formed; yield 1.46 g after crystallization from EtOH (20 ml)/ether (50 ml). Better yields and purer product were experienced when the potassim phthalimide was added in form of a solution in formamide.

Example 23

Preparation of H₂N-F108-NH₂.

The compound of the previous Example 22 (1.46 g, 0.2 mEq) was dissolved in 9 ml EtOH, and there were added 0.1 ml

(2 mmol) of hydrazine hydrate. After one night at room temperature, the solution was diluted with 10 ml EtOH and refluxed for 3 hrs. Then the solvent was removed under reduced pressure, the residue was dissolved in 8 ml EtOH and a solid was precipitated by the addition of 40 ml ether. The solid was collected, washed with ether, dissolved in 8 ml ethanol, and 0.11 ml (2 mmol) of AcOH were added, the mixture was heated to 50°C, 50 ml of ether were added thereto and it was left to crystallize. White crystals (1.24 g) of diamino-F108 were collected and analyzed. Titration of the -NH2 groups showed that the substitution was substantially 100%.

Example 24

(a) Preparation of (AfW) linker-magnetite particles. In 40 ml of water, there were dissolved 81.1 mg (0.3 mmole) of FeCl₃.6H₂O and 56.9 mg (0.3 mmole) of

FeCl₂.4H₂O. (total Fe = 0.6 mmole or 33.5 mg) To this were added 0.1 mCi of 59p_e (tracer quantity) in the form FeCl₃.

The mixture was stirred and an aqueous 7.5% solution of ammonia was added dropwise until the pH reached a stable value of 8.6. A suspension of black particles formed which was heated for 5 min at 75°C and the particles were allowed to settle at room temperature. The precipitate was washed three times by decantation with portions of 100 ml of water, after which it was again suspended in 60 ml of water under agitation. The iron concentration of this suspension was 0.5 mg/ml.

To 10 ml of this suspension (5 mg of Fe) were added (as component (a) 100 mg of the sodium salt of dipalmitoylphosphatidic acid (DPPA-Na) and sonication was effected for 20 min (BRANSON 250 Sonifier, 1/8" microprobe, output 20 (15-20 W). The temperature which rose to about 68°C during sonication was allowed to drop to room temperature, and there were added (as component (b) 100 mg of Pluronic®- (NH₂)₂ as prepared in Example 23 (or identically modified amphiphiles such as Synperonic® (from ICI), or Poloxamer®-338). Sonication was then resumed for 15 min under the aforementioned conditions.

The obtained suspension of coated particles (Sample SBPA-NH₂ [or SBPA 0.5/10/10]) therefore contained, per ml, 0.5 mg of iron, 10 mg of DPPA and 10 mg of the derivatized Pluronic® (NH₂)₂ surfactant (weight ratio of (a) to (b) = 1:1). Measurements by means of a particle counter apparatus (Nicomp 370 HDL-NPSS of Particle Sizing Systems, Santa Barbara, California, USA) indicated that, depending on the run, the average particle size was in the range 50 - 100 nm (± 20-40%).

Example 25

Preparation of SBPA-maleinimidophenyl-butyramide

Ten ml of sample SBPA-0.5/10/10 (see above under a) were centrifugated for 1 hr under 27 '000 g. The undernatant residue was taken with 100mM HEPES buffer (pH 7.0) and diluted to 2 mg Fe/ml. To this were added 2.5 μmole of sulfosuccinimidyl-4[p-maleinimidophenyl]-butyrate(sulfo-SMPB) and the mixture was incubated for 2 hrs at r.t. Excess reagent was eliminated by adding EDTA (10 mM) and centrifugation (2 min, 100g). The residue was resuspended in HEPES (2.5 mg Fe/ml).

Example 26

Preparation of the S-acetylthioacetate of the hexapeptide f-Nle-Leu-Phe-Nle-Tyr-Lys.

The hexapeptide (6 μmol) was dissolved in DMSO to make a concentration of 10 mg/ml and 1 equiv. of N-hydroxysuccinimidyl-S-thioacetate (SATA) in the form of a 14 mg/ml DMSO solution was admixed; thereafter, N-ethylmorpholine was added to bring the appsarent pH to 8

(moist pH strip). After 1 hr, the mixture was dilute 20 fold with H2O and loaded on a HPLC chromatography cartridge equilibrated in water (C18 Bond Elut cartridge, eluent 80% aqeous acetonitrile). The thioacetylated peptide appeared in the 18.77 min fraction which was dried to a solid; the latter was redissolved in a little DMSO.

Example 27

Preparation of the hexapeptide coupled to the SBPA magnetite particles.

The hexapeptide S-acetylthioacetate (2 mg) in DMSO solution was added to a HEPES solution of the SBPA- maleininimide derivatized iron oxide particles (2.5 mg Fe) prepared as disclosed in Example 25. The HEPES buffer used also contained EDTA (2.5 mM) and hydroxylamine (50 mM); the hydroxylamine acts as a deacetylation reagent. The mixture was kept at room temperature for 2 hrs, then the iron oxide particles were isolated by centrigugation, resuspended in buffer and extensively dialyzed for purification.

Example 28

Testing of the magnetite-chemoattractant peptide conjugate affinity with granulocytes.

Tissue injury and inflammation by bacterial infection induce granulocyte (PMN) and mononuclear phagocyte formation in response to the chemotactic peptides produced on the infection site. Granulocytes are known to produce O₂ ^-· radicals which can be assayed by the reduction of the dye Nitro Blue Tetrazolium (NBT) absorbing at 540 nm.

Neutrophils were isolated from fresh buffy coats and cultured according to Magn. Res. Imaging 13 (1995), 393-400. The rate of NBT reduction was measured directly in the cells cultured in microplates. The assay media comprised 150 μl of NBT solution (2 mg/ml); 100 μl of the conjugate solution (this including various concentration samples); to which were added 50 μl of PMN (2.5-10⁵ cells) lodoacetamide (an inhibitor of oxidative burst) was added to the medium in the photometer reference well (to 10 mM final concentration), the cells having been preincubated for 10 min at 37°C in 10 mM iodoacetamide. The details of the assay are disclosed in "Methods in Enzymology" 132 (1995), 417.

In the graph (a) of Fig 6, there are respectively shown the rates of O₂ ^-· production by granulocytes in response to various dlutions (identified by the iron concentrations) of the SBPA-chemoattractant synthetic peptide. The capacity of PMN to be stimulated in a dose-dependent manner by the SBPA-hexapeptide is evidenced of the presence of the magnetite particles coupled to the chemoattractant. In the controls (b), the effect of the magnetic particles alone, uncoupled to the peptide, is virtually naught. Fig 6 (a) Fig 6 (b)

The foregoing results have been further confirmed by radioactivity measurements ( ⁵⁹Fe-labeled conjugates) and T₂ proton relaxation parameters (NMR). For these experiments, frshly purified human PMN was incubated for 1 hr at 37°C with various SBPA-peptide conjugates, then washed in cold PBS. The T₂ measurements showed that the incorporation/association of iron from the conjugate was 6 to 43 times greater than with uncoupled magnetite particles.

In laboratory rats, tracer measurements after intraveinous injection of ⁵⁹Fe-SBPA-hexapeptide samples showed a preferential transfer of the iron through the circulation toward traumatized sites.

Example 29

Conjugation of Gd(III) complexes of linear polyaminocarboxylates (e.g. DTPA and DTPA.BMA) with chemotactic peptides.

The isothicyanate DTPA derivative, (ITC-DTPA, Structure I) is synthesized according to M.W. Brechbiel et al. in Inorg. Chem. 25 (1986), 2772 or Bioconj. Chem. 2 (1991), 187. The Gd(III) complex of ITC-DTPA is prepared in situ by mixing equimolecular quantities of the ligand and GdC13 in a suitable solvent ad raising the pH of the mixture slowly. The conjugation of the chelate and the chemotactic peptide (see the previous Examples), and its final purification, is achieved according to the method given in the next Example for the conjugation of Gd(IPA-DO3A). ITC-DTPA is made by usual means from the corresponding aniline (Structure II)

For this, (1) the amino group of the aniline derivative is protected, for instance with BOC; then (2) the pentaacetic acid is converted to its cyclic bisanhydride according to W.C. Eckelman et al. in J. Pharm. Sci. 64 (1975), 704. The bisanhydride is then reacted (3) with an alkylamine RNH₂ (in which R is C_1-6 Alk) according to US-A-5,087, 439 (S.C. Quay) incorporated herein by reference to provide a bisalkylamide the protecting group is then removed to give the compound of Structure III.

Then, after converting the foregoing to the corresponding isothiocyanate to be used as ligand to chelate with Gd(III) as mentioned already, the latter complex can be conjugated to a chemotactic peptide by following the general procedure given in Example 30, below. Example 30

Conjugation of chemotactic peptides with amino-dendrimers

A chemotactic peptide is activated according to Scheme I below.

The following steps are involved: (1) The reaction of p-nitrobenzoyl chloride with the chemotactic peptide; (2) the catalytic hydrogenation of the nitro group to the corresponding aniline, and (3) reaction of the latter with thiophosgene to give the isocyanato derivative. The activated peptide is then reacted in the presence of a base with an amino-terminated dendrimer (see Magnetic Resonance in Medicine 31 (1994) to achieve reaction (thiourea bonds) on a few dendrimer amino-functions. The remaining dendrimer end sites can be conjugated with the activated Gd-chelated moieties, e.g. Gd(IPA-DO3A) to provide a polytargeted-polychelated dendrimer, i.e an example whith multiple signal generators attached to peptides that can bind to receptors.

Example 31

Conjugation of chemotactic peptides with superparamagnetic iron particles

Dextran coated magnetite particles are disclosed in US-A-5,219, 554 (E.V. Groman et al.). The derivative 1-[(4-isothiocyanatophenethyl)amino]dihydrodextran (Structure IV) is synthesized according to J.S. Mann et al. in Bioconj.Chem. 3 (1992), 154 and this activated dextran can be bound to a chemotactic peptide with desired length and distribution of aminoacids using the conjugation procedure oulined in previous Examples.

Then the peptide derivatized dextran can be used to coat magnetite particles, thus providing magnetite particles targeted toward sites of production of receptors.

Claims

1. Marker labeled chemotactic peptide compounds for the detection and investigation of diseased or disordered sites in human and animal organisms of general formula (F)

N(X)-Y-Leu-Phe-Z-A-W (F) wherein X is H or a protective group such as formyl, acetyl, t-Boc, or the like; Y is Nle or Met; Z is a chemical bond, an aminoacid or an oligopeptide, e.g. (N(γ))Lys, lie,

Asp, Nle-Tyr-Lys, or (Gly)_n, n being 1 to 4; A is a bond or a linker; and W is a suitably derivatized macrocyclic chelate of paramagnetic ions or magnetic particle.

2. The compounds of claim 1, wherein the macrocyclic chelates (W) are selected from (a) complexes of paramagnetic ions with 1,4,7,10-tetraazacyclododecane ring compounds of formula I

in which X is an alkyl substituent carrying one or more oxygen containing functions; or (b) Starburst® dendrimers of the following structure (II):

in which at least one R is A of formula (F), the other R's being derivatized chelates of paramagnetic metals, e.g.isothiocyanato-DTPA (ITC-DTPA), SCN-Ph-NH-CO-CH₂-DO3A (IPA-DO3A), or having the formula

Ac being acetyl.

3. The compounds of claim 2, wherein the chelates of formula I

are selected from the following structures

4. The compounds of claim 1, wherein the paramagnetic ions are selected from lanthanides including Gd, and suitable other transition elements, including Cu, Mn, Cr, Co, Ni, Fe, Pd and the like.

5. The compounds of claim 1, wherein W represents magnetic particles selected from polymer coated or silanized submicronic ferrites or magnetites.

6. The compounds of claim 1, wherein linker A is selected from chemical bonding units or sequences having required functions to provide a bridge between the peptides and the macrocyclic chelate molecules.

7. The compounds of claim 6, wherein the bonding units are selected from one or more of -S-, -NH-, -NHN=, NHCONHN=, -CONH-Ph-NH-CO-, NHCSNHN=,

, NC(O)-, NC(S)-, -CO-, Het1, -C(Het2)CH2

8 . A method for making the compounds of claim 1 , which comprises reacting a first moiety of targeting chemotactic peptides , a second moiety comprising a magnetically responsive label and a bridging compound to provide linker A between first and second moieties , wherein the reactions involve functions of said moieties and/or said bridging compound selected from acid halides , anhydrides , amides , imides , esters , amines , carbodiminmides , isocyanates , isothiocyanates , derivatized maleinimides and succinimides , and the like .

9. The method of claim 8, wherein the reactions are one or more of the following schemes:

10. The method of claim 8 comprising one or more of the following routes:

a)

Peptide N-hydroxysuccinimide carboxylate ester and aminoderivatized chelatant molecule H₂-R'

Sulfo-SMBP (4-(4-maleinimidophenyl)-N-sulfosuccinimidyl butyrate, aminoderivatized chelatants H₂R'

and HS-peptides c) Chelatants mixed anhydrides R'-CO-O-CO-R' (obtained from chelatant tetramethylguanidine salts and isobutyl chloroformate) and peptides having lysine functional -NH₂.

Peptides thiolated by 2-iminothiolane , aminoderi

vatized chelatants H₂N-R', and succinimidyl-4-(N-maleinimidomethyl)-cyclohexane-1-carboxylate

e) Derivatisation of chelatant R' by reaction of intra- or intermolecular cyclic anhydride R'-CO-O-CO-R' with alkylene diamine, introduction of a 2-pyridyldisulfide group with N-succinimidyl-3-(2-pyridyldithio)-propionate (SPDP) and coupling with thiolated chemotactic peptide to form a covalent thia-bonded conjugate, this being as follows: R'CONH-Alk-NH₂ + SPDP ➨ R'CONH-Alk-NH-CO-CH₂-SSPyr

R'CONH-Alk-NH-CO-CH₂-SSPyr + RSH ➨ R'CONH-Alk-NH-CO-CH₂-SR.

11. The method of claim 8 in which the magnetically responsive label is constituted by submicronic particles silanized by means of one or more of trialkoxy silanes selected from isocyanatoalkylsilanes, isothiocyanoalkylsilanes, 3-aminopropyltrimethoxysilane, hydroxypropyltriethoxysilane, 4-chlorobutyltrimethoxysilane and the like.

12, A method of MRI investigation, either by in vivo injection, or by ex vivo labeling, which comprises using labeled peptides according to claim 1.