EP0971947A2

EP0971947A2 - Rink-chloride linker for solid phase organic synthesis of organic molecules

Info

Publication number: EP0971947A2
Application number: EP98913115A
Authority: EP
Inventors: Ravi S. Garigipati
Original assignee: SmithKline Beecham Corp
Current assignee: SmithKline Beecham Corp
Priority date: 1997-03-28
Filing date: 1998-03-26
Publication date: 2000-01-19
Also published as: WO1998044329A2; JP2001518946A; WO1998044329A3; CA2285175A1; EP0971947A4

Abstract

This invention relates to a novel linker for use in solid phase chemistry, its preparation and methods of use of the linker.

Description

RINK-CHLORIDE LINKER FOR SOLID PHASE ORGANIC SYNTHESIS OF ORGANIC MOLECULES

FIELD OF THE INVENTION This invention relates to a novel linker for use in solid phase chemistry, its preparation and methods of use of the linker.

BACKGROUND OF THE INVENTION

In the continuing search for new chemical moieties that can effectively modulate a variety of biological processes, the standard method for conducting a search is to screen a variety of pre-existing chemical moieties, for example, naturally occurring compounds or compounds which exist in synthetic libraries or databanks. The biological activity of the pre-existing chemical moieties is determined by applying the moieties to an assay which has been designed to test a particular property of the chemical moiety being screened, for example, a receptor binding assay which tests the ability of the moiety to bind to a particular receptor site.

In an effort to reduce the time and expense involved in screening a large number of randomly chosen compounds for biological activity, several developments have been made to provide libraries of compounds for the discovery of lead compounds. The chemical generation of molecular diversity has become a major tool in the search for novel lead structures. Currently, the knownjnethods for chemically generating large numbers of molecularly diverse compounds generally involve the use of solid phase synthesis, in particular to synthesize and identify peptides and peptide libraries. See, for example. Lebl et al., Int. J Pept. Prot Res . 41, p. 201 ( 1993) which discloses methodologies providing selectively cleavable linkers between peptide and resin such that a certain amount of peptide can be liberated from the resin and assayed in soluble form while some of the peptide still remains attached to the resin, where it can be sequenced; Lam et al., Nature. 354. p 82 ( 1991 ) and (WO 92/00091 ) which disclose a method of synthesis of linear peptides on a solid support such as polystyrene or polyacryiamide resin; Gevsen et al., J. Immunol. Meth , 102. p. 259 ( 1987) which discloses the synthesis of peptides on deπvatized polystyrene pins which are arranged on a block in such a way that they correspond to the arrangement of wells in a 96-well microtiter plate, and Houghten et al., Nature. 354, p 84 (1991) and WO 92/09300 which disclose an approach to de novo determination of antibody or receptor binding sequences involving soluble peptide pools.

The major drawback, aside from technical considerations, with all of these methods for lead generation is the quality of the lead. Linear peptides historically have represented relatively poor leads for pharmaceutical design. In particular, there is no rational strategy for conversion of a linear peptide into a non-peptide lead. As noted above, one must resort to screening large databanks of compounds, with each compound being tested individually, in order to determine non-peptide leads for peptide receptors.

In this respect, there has been increasing interest in the application of solid phase synthesis to the preparation of organic compounds, especially in the context of combinatorial chemistry and multiple simultaneous synthesis, or parallel synthesis. One of the limitations in the solid phase approach in general, involves the linker by which the organic molecule is attached to the solid support. The Rink linker (Rink, H., Tetrahedron Lett., 1987,25, 3787-3790) has been effectively applied to the synthesis of some chemical libraries (Gordeev, M. F.; Patel, D. V.; Gordon, E. M. J. Org. Chem. 1996, 61, 924-928; Norman, T C, Gray, N. S.; Koh, J. T.; Schultz, P G. f Am Chem. Soc. 1996, p. 118. 7430-7431, Ward, Y. D.; Farina, V Tetrahedron Lett., 1996, 57, 6993-6996), because of the ease of use and mild conditions for release of the library component. However the Rink linker is currently limited to use in the preparation of amides and carboxy c acids. Therefore, a need exists for a Rink linker useful for a broader range of solid phase chemistry. Herein, we describe the preparation of a Rink-chloπde linker, which allows a very general and practical method for the attachment of, inter alia, amines, alcohols and thiols to a solid support.

SUMMARY OF THE INVENTION

This invention relates to a novel solid phase Rink linker of formula (I), hereinafter referred to as a resin-bound Rink-chloπde linker or a Rink-chloπde linker This represents a significant improvement over the current use of the Rink- acid linker. At present the use of the known Rink-acid linker is limited to preparing amides and carboxyhc acids. The use of the instant improved Rink-chloπde linker of formula (I) makes Rink technology available to a broad number of functional group attachments. The use of the Rink-chloπde linker allows a very general and practical method for the attachment of amines, alcohols and thiols, including phenols and thiophenols to a solid support. Therefore, another aspect of the instant invention is in a method for making compounds by resin-bound synthesis using the Rink- chloπde linker in solid phase synthesis. This method is applicable to making combinatorial libraries of compounds designed around a core molecular structure using known methods of solid phase combinatorial chemistry or multiple simultaneous synthesis ("parallel synthesis") The compounds or libraries of compounds made using this linker may be tested in biologically assays designed to test for a particular physical characteristic potentially useful in drug therapy

DETAILED DESCRIPTION OF THE INVENTION The terms "resin." "solid support." "inert resin, ' polymeric resin" or

"polymeric resin support" are used herein at all occurrences to mean a bead or other solid support such as beads, pellets, disks, capillaries, hollow fibers, needles, solid fibers, cellulose beads, pore-glass beads, silica gels, grafted co-poly beads, polyacryiamide beads, latex beads, dimethylacrylamide beads optionally cross-linked with N,N'-bιs-acryloyl ethylene diamine, glass particles coated with a hydrophobic polymer, etc., i.e., a material having a rigid or semi-rigid surface. The solid support is suitably made of, for example, cross linked polystyrene resin, polyethylene glycol- polystyrene resin, and any other substance which may be used as such and which would be known or obvious to one of ordinary skill in the art. The term 'substituted resin-bound Rink-chloπde intermediate" is used herein at all occurrences to mean the intermediate produced by coupling a resin-bound Rink-chloπde linker with a suitable nucleophile (with displacement of the chloride of the Rink linker) such that to the nucleophile is linked to the resin through the Rink linker. The term "additional synthetic chemistry" is used herein at all occurrences to mean chemical reactions which are performed on the substituted resin-bound Rink- chloπde intermediate prior to cleavage of the nucleophile from the polymeric resin, wherein said chemical reactions are compatible with and non-reactive with the Rink- chloπde linker and may be used to prepare derivatives of the nucleophile It will be understood by the skilled artisan that the additional synthetic chemistry performed on the substituted resin-bound Rink-chloπde intermediate, is done so prior to cleavage of the deπvatized nucleophile. Chemical reactions which are incompatible with the nucleophile/Rink-chloπde linkage, i.e., they cause cleavage of the nucleophile from the Rink-chloπde linker, are not among the additional synthetic chemistry that may be used in the methods of this invention

The terms "resin-bound synthesis" and "solid phase synthesis" are used herein interchangeably to mean a series of chemical reactions used to prepare either a single molecule/compound or a library of molecularly diverse compounds, wherein the chemical reactions are performed on a compound which is bound to a polymer resin through a linkage, in particular, a Rink-chloπde linkage

Chemical synthesis on solid supports has become a cornerstone in the generation of small organic molecule combinatorial libraries Paramount to the success of any sohd- phase synthetic strategy is a reliable and general method for coupling the initial starting materials onto the solid support, namely through linker technology Such linker technology should also be amenable to ready cleavage of the reaction products under relatively mild conditions, and without compromising the structure of the reaction products The Rink linker has been effectively applied to the synthesis of some chemical libraries because of its ease of use and the mild conditions for release of library components from the solid support However the Rink technology is currently limited to the preparation of amides and carboxyhc acids Herein, we describe the preparation and utility of a Rink-chloπde linker, which allows a very general and practical method for the attachment of amines, alcohols and thiols to a solid support, deπvatization of these resin- bound compounds, and their eventual release from the resin with tnfluoroacetic acid

The resin-bound Rmk-acid linker 1-Scheme 1 can be converted to the resin-bound Rink-chloπde resin of this invention, 2-Scheme 1, by treatment of the resin-bound Rink- acid linker with tπphenyl phosphine and hexachloroethane 2-Scheme 1 so obtained is stable at room temperature for several days and can be used without any loss of activity

Scheme 1

2-Scheme 1 can be reacted cleanly with a variety of nucleophiles ("Nu") under mild reaction conditions (see. Scheme 2 and Table I below) The nucleophiles depicted herein are either commercially available or can be made using known procedures

Scheme 2

Table I

Rink-chloride efficiently reacts with primary and secondary amines, anilines, alcohols, phenols, thiols, thiophenols, and carboxyhc acids. The coupling is usually carried out in dichloroethane in the presence of Hunig's base, under inert atmosphere for 18-26 hours at room temperature. The extent of coupling efficiency is monitored by MASNMR and then by cleaving the product from the resin with about 3-5% TFA in CHoCb- Release of the ligands from the resin is complete within 30 minutes as evidenced by MASNMR of the residual resin. As is apparent from Table I, the coupling is general and highly efficient. While cleavage from the resin is facile, it is sufficiently stable enough to carry out a wide range of chemistry commonly used in small molecule library construction. Some illustrative examples are shown in Scheme 3.

Scheme 3

1. FMOC-glyine acid chloride/ Hunig's base

2. 20%pιperιdιne m DMF

0

It will be understood that after making the substituted resin-bound Rink- chloride intermediate, and prior to cleavage with TFA. additional syntheic chemistry may be performed on the intermediate in order to derivatize the nucleophile core. Therefore, another aspect of the invention is in a method for synthesizing a 5 compound by resin-bound synthesis comprising the steps of: (a) converting a resin- bound Rink-acid linker into a resin-bound Rink-chloride linker of formula (I)

(b) coupling the resin-bound Rink-chloride linker with a suitable nucleophile under appropriate conditions to provide a substituted resin-bound Rink-chloride intermediate; and (c) performing additional synthetic chemistry on the substituted resin-bound Rink- chloride intermediate to provide a resin-bound derivatized nucleophile. The resin-bound derivatized nucleophile can remain bound to the resin for storage and/or further derivatization, or it may be cleaved from the resin with between about 3 and 5% TFA.

In yet another aspect, this invention is in a method for synthesizing a library of molecularly diverse compounds by resin-bound synthesis, comprising the steps of: (a) converting a resin-bound Rink-acid linker into a resin-bound Rink-chloride linker of formula (I)

(b) coupling the resin-bound Rink-chloride linker with a suitable nucleophile under appropriate conditions to provide a substituted resin-bound Rink-chloride intermediate; (c) optionally dividing said substituted resin-bound Rink-chloride intermediate into a plurality of portions; (d) performing additional synthetic chemistry on the substituted resin-bound Rink-chloride intermediate to provide a resin-bound derivatized nucleophile; and (e) optionally recombining the portions. Based upon the disclosure herein, it will be clear to one of ordinary skill in the art that there are many possible synthetic approaches to creating the libraries of this invention. For example the libraries may be prepared using the split and mix technique or parallel synthesis techniques. The libraries generated from either of the the synthetic methods are molecularly diverse and are prepared simultaneously. The libraries are prepared on the polymer resins using the Rink-chloride linker described herein. For example, the compound to be derivatized (suitable nucleophile), is attached to the polymer resin through the Rink-chloride linker to give a substituted resin-bound Rink-chloride intermediate. In one embodiment, the substituent(s) are modified by reacting the resin-bound Rink-chloride intermediate, with a mixture of reagents. In an alternative embodiment, aliquots of the resin-bound Rink-chloride intermediate are reacted with individual reagents each one of which will modify a position on the core of the resin-bound nucleophile, and then the resultant products are mixed together to form the library of derivatized resin-bound intermediates. This library may then be further derivatized by repeating the process of dividing and recombining the intermediates formed by the additional synthetic chemistry. It will be clear to one of ordinary skill in the art that when the libraries of the invention are prepared according to the instant disclosure, each polymer support bears a single species created by the additional synthetic chemistry performed on the substituted resin-bound Rink-chloride intermediate.

It will be obvious to one of skill in the art that the steps of optionally dividing and recombining the resin-bound aryl silane intermediate into portions are for purposes of varying the derivatization on the resin-bound nucleophiles which are generated by the combinatorial synthesis. Of course, it will be obvious to the skilled artisan that the resin-bound nucleophile intermediates may be divided into portions at any point during the synthetic sequence. The portions may be recombined at any point during the sequence or, further iterations may be applied if more derivatization is required. Therefore, it will be obvious to the skilled artisan that the steps of dividing the portions, performing additional synthetic chemistry and recombining the portions, may each be carried out more than once, depending upon the type of diversity required for the library of end-product compounds being prepared. According to this invention, after the additional synthetic chemistry has been performed on the resin-bound aryl silane intermediate so that a library of molecularly diverse compounds has been prepared, the compounds can be separated and characterized by conventional analytical techniques known to the skilled artisan, for example infrared spectrometry or mass spectrometry. The compounds may be characterized while remaining resin-bound or they can be cleaved from the resin using the conditions described above, and then analyzed. In addition, a partial array of compound members of the library may be cleaved from the resin, characterized and analyzed, while leaving a partial array of the compound members of the library bound to the resin. EXAMPLES Preparation of Rink-chloride (2-Scheme 1)

To a suspension of resin-bound Rink-acid, 1-Scheme 1, (l.Og, l.όmmol.) in THF (25mL) was added triphenylphosphine (2.32g, 8.8mmol.) and hexachloroethane (2.13g, 8.8mmol.). The reaction mixture was agitated with a constant flow of argon for 6h. The resin-bound Rink-chloride, 2-Scheme 1, was filtered and washed with THF and acetone. Completion of the reaction was affirmed by chlorine analysis and MASNMR (the signal for CH(OH)at δ 5.85 disappears completly). Chlorine analysis indicated a stoichometric amount of chlorine.

Reaction of rink-chloride with various nucleophiles

To a suspension of 2-Scheme 1 (0.96g, l.όmMol.) in dichloroethane (25mL) was added Hunig's base (lmL) and the requisite nucleophile (lOmMol.). The reaction mixture was agitated with a constant flow of argon for 6-12h. The resin was filtered and washed with dichloromethane, MeOH, H2O, EtOH, CH2CI2 and MeOH.

Completion of the reaction was confirmed by MASNMR, IR or elemental analysis. Elemental analysis indicates no chlorine and a stoichometric amount of nitrogen or sulfur for the appropriate compounds.

Cleavage from Rink-linked ligands

3% TFA/CH2CI2 was added to the substituted resin-bound Rink chloride moieties, either as individual beads or in bulk quantity. The cleavage was carried out for 30 min., and the product was isolated by extraction with 1: 1/ MeOH:MeCN. All the cleaved products from Table I were identified by comparing them with an authentic sample of the starting material (nucleophile).

The above description fully discloses the invention including preferred embodiments thereof. Modifications and improvements of the embodiments specifically disclosed herein are within the scope of the following claims. Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. Therefore any examples are to be construed as merely illustrative and not a limitation on the scope of the present invention in any way. The embodiments of the invention in which an exclusive property or privilege is claimed, are defined as follows.

Claims

What is claimed is:

1. A resin-bound compound of formula (I)

2. The resin-bound compound of formula (I) as claimed in claim 1 , made by a method comprising reacting a resin-bound Rink-acid linker with triphenyl phosphine and hexachloroethane.

3. A method for synthesizing a compound by resin-bound synthesis comprising the steps of:

(a) converting a resin-bound Rink-acid linker into a resin-bound Rink- chloride linker of formula (I)

(b) coupling the resin-bound Rink-chloride linker with a suitable nucleophile under appropriate conditions to provide a substituted resin-bound Rink-chloride intermediate; and

(c) performing additional synthetic chemistry on the substituted resin-bound Rink-chloride intermediate to provide a resin-bound derivatized nucleophile.

4. The method as claimed in claim 3, further comprising the step of cleaving the derivatized nucleophile from the substituted resin-bound Rink-chloride intermediate.

5. A method for synthesizing a compound by resin-bound synthesis comprising the steps of:

(b) coupling the resin-bound Rink-chloride linker with a suitable nucleophile under appropriate conditions to provide a substituted resin-bound Rink-chloride intermediate;

(c) performing additional synthetic chemistry on the substituted resin-bound Rink-chloride intermediate to provide a resin-bound derivatized nucleophile; and

(d) cleaving the resin-bound derivatized nucleophile.

6. A method for preparing a library of diverse compounds by resin- bound synthesis, comprising the steps of:

(c) optionally dividing said substituted resin-bound Rink-chloride intermediate into a plurality of portions;

(d) performing additional synthetic chemistry on the substituted resin-bound Rink-chloride intermediate to provide a resin-bound derivatized nucleophile; and (e) optionally recombining the portions.

7. The method of claim 6 wherein the steps of (c) dividing the portions, (d) performing additional synthetic chemistry, and (e) recombining the portions, are carried out more than once.

8. The method of claim 5 wherein the derivatized nucleophile is cleaved from the resin-bound Rink-chloride intermediate by reaction with between about 3 to 5% TFA.