AU2021103482A4

AU2021103482A4 - Amino acids and peptide conjugates of dopamine

Info

Publication number: AU2021103482A4
Application number: AU2021103482A
Authority: AU
Inventors: Vishal Dubey; Arpit KATIYAR; Abhinav Prasoon; Megha Tiwari
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-06-19
Filing date: 2021-06-19
Publication date: 2021-08-26
Anticipated expiration: 2029-06-19

Abstract

The present invention relates to the synthesis of series of novel amino acids and dipeptides conjugates of dopamine. Apart from this we also synthesized highly lipophilic conjugates of dopamine by increasing the number of carbon chain between amino-carboxylic group. It was an attempt to enhance the bioavailability of dopamine by increasing its permeability through blood brain barrier. The purity of all the prepared compounds were checked by TLC and elemental analyses. The spectroscopical data (UV, IR, 1H-NMR, MS and elemental analysis) of all the synthesized compounds were found in agreement with assigned molecular structures

Description

AMINO ACIDS AND PEPTIDE CONJUGATES OF DOPAMINE FIELD

[001] The present invention relates to the synthesis of series of novel amino acids and dipeptides conjugates of dopamine.

BACKGROUND

[002] Category of neurodegenerative diseases includes Alzheimer disease, Parkinson's disease, Huntington disease, and amyotrophic lateral sclerosis. These devastating illnesses are Parkinson's disease is a common neurodegenerative disease. The vast characterized by the progressive loss of selected neurons in discrete brain areas, resulting in characterize disorders of movement, cognition, or both. For example, Alzheimer disease is characterized by the loss of cholinergic neurons in the nucleus basalis of Maynert, whereas Parkinson disease is associated with a loss of dopaminergic neurons in the substantia niagra. The most prevalent of these disorders is Alzheimer, affecting some four million people. Parkinson disease is the second most frequent disorder, affecting approximately 1.5 million Americans.

[003] Epidemiology of Parkinson disease in the city of Kolkata, India: a community based study showed that the age-adjusted prevalence rate (PR) and average annual incidence rate were 52.85/100,000 and 5.71/100,000 per year, respectively. The adjusted average annual mortality rate was 2.89/100,000 per year. The relative risk of death was 8.98. The case-control study showed that tobacco chewing protected and hypertension increased PD occurrence.

[004] The Parsi community of Mumbai, India has a prevalence of Parkinson's disease of 328.3 per 100,000 populations, which is almost in excess of that found in Nebraska. This is despite India as a whole having a low prevalence due to the inhalation of Aspand seed fumes, as a part of their religion. Aspand seed is the richest natural source of two MAO Inhibitor alkaloids, harmine and harmaline, used in Parkinson's disease. Long term use of MAO inhibitors, eventually has the opposite effect, and so may cause the high prevalence of Parkinson's disease amongst the Parsi.

[005] Nearly 40 years after levodopa or L-dopa introduction, remains an effective

Pharmacotherapy in Parkinson's disease. Development of L-dopa as a therapeutic agent in PD is a rare example of a rationally predicted and logically pursued clinical treatment in a neurological disorder, based on neurochemical pathology and basic Pharmacological theory. The effectiveness of L-dopa treatment requires its penetration into the central nervous system (CNS) and local decarboxylation to DA.

[006] Although L-dopa reduces many of the motor symptoms of PD, it does not affect non-motor symptoms and does not halt the progression of the degeneration of dopamine containing neurons in the substantia nigra (Wolters, 2000). Progression of Parkinson's disease advances (4-8 years), the efficiency of L-dopa decreases over time such that many patients develop motor fluctuations ('wearing-off and 'on-off phenomena) and dyskinesias, and patients no longer exhibit a stable and predictable clinical response. Therefore, increasing amounts and frequencies of doising of L-dopa are usually necessary to maintain the initial therapeutic response. It has also been postulated that L-dopa could be toxic to dopamine containing neurons. The therapeutic advantages and disadvantages of early versus delayed tretment with L-dopa are still debated.

[007] The development of a new drug involves three approaches (1) The general screening approaches in which chemical substances from any source are tested for their effect against predetermined disease or disease state, (2) The chemical modification of existing drug substance whose biological effects are known and (3) Mimicking the nature by biochemical design, where a compound is made to exert an action in a manner similar to a known biochemical substance. Any lead compound obtained from these three approaches is usually further modified chemically to gain the biologically most potent representative of the series.

[008] In the recent scenario, advances have taken place in the field of prodrug approach of dopamine to ensure whether dopamine conjugates with various amino acids are able to cross the blood brain barrier, so that the use of levo-dopa as the precursor of dopamine could be reduced, thus minimizing the side effect of levo-dopa. Levo-dopa has the most tremendous side effects. The literature survey reveals that not much work has been done on dopamine conjugation with amino acids and peptides. Such peptides may be comprised of units, which them selves are the part of various physiological processes. Such a conjugation may be helpful for the formulation of the targated drug delivery systems of dopamine in the brain.

[009] The following prior art is being reported:

[010] SG11201704962W: The present invention relates to peptides, and amino acid and peptide conjugates, methods for making amino acid and peptide conjugates, conjugates produced by the methods, pharmaceutical compositions compris, ing the peptides and conjugates, methods of eliciting immune responses in a subject and methods of vaccinating a subject, uses of the peptides and con, jugates for the same, and uses of the peptides and conjugates in the manufac - ture of medicaments for the same.

SUMMARY

[011] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[012] An embodiment of the present invention is generally directed to the synthesis of Fourteen compounds for anti-Parkinson's activity. They have amino acids and dipeptides conjugate of dopamine. Besides, highly lipophilic conjugates of dopamine were synthesized by increasing the number of carbon chain between amino-carboxylic group (chain elongation).

[013] An embodiment of the present invention is the synthesized compounds were characterized by FTIR to identify the functional groups and 1H-NMR to identified the number and nature of protons present in the synthesized compounds.

[014] Another embodiment of the invention is the IR spectra of the compounds, the N-H stretching and bending and C=O stretching bands were observed at 3325-3276, 1635 cm-i respectively.

[015] Yet another embodiment of the invention is 1H-NMR spectra were recorded at 400.13 MHz.

DESCRIPTION OF EMBODIMENTS

[016] The following description is of exemplary embodiments only and is not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention.

[017] various conjugates were synthesized by using conventional solution phase peptide synthesis. To obtain compounds DA-1 to DA-6, the following sequence was taken. Initially, amino group of an amino acid was protected by Boc anhydride then conjugation with dopamine hydrochloride in the presence of DCC was carried out, which was shown in Scheme.l.

00

RAHr OH HO NH 2 R OH (i) HONH NH

NH 2 HO 0

a 1

NH N HO NH HO NH2 4H HOX HDO

[018] Scheme 1. showing Synthesis of Compounds used reagents and conditions, (i) triethyl amine (2 ml) and methanol, 40 C; (ii) N, N'-Dicyclohexylcarbodiimideat 0°C (iii) 4N Hydrochloric Acid in dioxane.

[019] In the second scheme dopamine was conjugated with increasing number of carbon chain between amino-carboxylic group i.e. Beta-alanine, gama amino butyric acid, 5 amino pentanoic acid and amino caproic acid by protecting amino group with Boc anhydride. In the above compounds lipophilicity increases with increase in number of carbon atoms and synthesis was carried in the presence of DCC, which was shown in scheme 2.

0 0 NH 2 HN R OH HO H2N R OH (i)

o o o 0 HO

N H

0 00 0 0

HO HO

[020] Scheme.2. showing the Synthesis of Compounds used reagents and conditions, (i) triethyl amine (2 ml) and methanol, 40°C; (ii) N,N'-Dicyclohexylcarbodiimideat 0°C(iii) 4NHydrochloric Acidin dioxane.

[021] Inthe third scheme dopaminewas conjugated withdipeptides. Aminoacids methyl ester hydrochloride was prepared. The other amino acids were N-protected using Boc anhydride. In the next step the N-protected amino acids and amino acids methyl ester hydrochloride were conjugated in the presence of DCC, which was shown in scheme.3.

R' R'

+ CH3 0H soc H2 N COOH H 2N COOCH 3 .HCI

0

R OH NH

NH + H 2N COOCH 3 .HCI

a N___ N__ y _

0 R 0 R __y H __, H N COOCH 3 N COOH

H H 0 R' 0 R'

[022] For determination of partition coefficients, the drug and synthesized compounds (10 mg) were taken in glass stopper tubes containing equal volumes (10 ml) of n-octanol and PBS pH 7.4. The tubes were shaken for 6 h on wrist action shaker. After 24 h, aqueous phase was assayed for the concentration using a UV-VIS spectrophotometer at corresponding absorption maxima.

[023] The purity of the compounds was checked by TLC and elemental analyses. The synthesized compounds were analyzed using UV-VIS spectrophotometer, FTIR spectrophotometer to identify the functional groups and IH-NMR to identified the number and nature of protons present in the synthesized compounds. The molecular ion peaks were identified using Mass spectral analysis.

[024] In the IR spectra of the compounds, the N-H stretching and bending and C=O stretching bands were observed at 3325-3276, 1635 cm-1 respectively. N-H stretching frequency of the -CO-NH- grouping was observed between 3360-3260 cm- 1. Structures of the compounds were further confirmed by Mass spectroscopy wherein M* and M+1 peak was obtained.

[025] Elemental analyses were carried out. The results of the elemental analysis (C, H, and N) were within 0.4% of the calculated amounts. The spectroanalytical data (UV, IR, 1H-NMR, MS and elemental analysis) of all the synthesized compounds were found in agreement with assigned molecular structures.

[026] EXAMPLE 1:

[027] Synthesis of 2-Amino-N-[2-(3, 4-dihydroxy-phenyl)-ethyl]-propionamide (DA-1)

[028] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15 mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-alanine (1.89 g, 10 mmol). After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10 mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether.

[029] EXAMPLE 2

[030] Synthesis of 2-Amino-N-[2-(3, 4-dihydroxy-phenyl)-ethyl]-acetamide (DA-2)

[031] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15 mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-glycine (1.75 g, 10 mmol). After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10 mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether.

[032] EXAMPLE 3: Synthesis of 2-Amino-N-[2-(3, 4-dihydroxy-phenyl)-ethyl]-3 phenyl-propionamide (DA-3)

[033] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15 mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-phenylalanine (2.65 g, 10 mmol). After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10 mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether.

[034] EXAMPLE 4: Synthesis of 2-Amino-N-[2-(3, 4-dihydroxy-phenyl)-ethyl]-3-(1H indol-3-yl)-propionamide (DA-4)

[035] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15 mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-tryptophane (3.04 g, 10 mmol). After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10 mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether.

[036] EXAMPLE 5: Synthesis of 2-Amino-3-methyl-pentanoic acid [2-(3, 4-dihydroxy phenyl)-ethyl]-amide (DA-5)

[037] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15 mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-isoleucine (2.31 g, 10 mmol). After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10 mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether.

[038] EXAMPLE 6: Synthesis of 2-Amino-N-[2-(3, 4-dihydroxy-phenyl)-ethyl]-3 methyl-butyramide (DA-6)

[039] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15 mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-valine (2.17 g, 10 mmol). After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10 mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether.

[040] General structure of amino acids with conjugates of dopamine

R R 5 7 H HO N 4 9610 NH 2 1 O HO 3 2

[041] Table.1. Molecular Formula, Yield, Melting point, Rf, UV, Log P and Elemental analysis (%) (C, H, N)

Co R Mol. Mol. Mass Rf UV log Element

mp formula weigh Spectr Valu Xma P al s Yield(%) t a e x Valu analysis obtaine e (0) Mp( 0 d d C) (C,H, N)

D -CH3 CiiH 16N 2 224.2 m/z, 0.44 285. 0.53 58.91, A- 03 6 224 5 9 7.19, 73 1 12.49 212 214

D -H CioH 1 4N 2 210.2 [M+1]* 0.42 269. 0.44 57.13, A- 03 3 m/z, 0 1 6.71, 78 2 211 13.33 218 220

D -CH2 -C 6H5 C 17 H 20N 2 300.3 [M+1]* 0.38 272. 1.92 67.98, A- 03 6 m/z, 5 2 6.71, 80 3 301.4 9.33

226

D -CH2 - C8H 6N C 19 H 2 1N 3 339.4 m/z, 0.41 265. 2.07 67.24, A- 03 340 5 2 6.24, 68 204 4 12.38 206

D -CH2- CH2-CH£1 4H 22N 2 266.4 m/z, 0.48 288. 1.74 63.13, A- CH3 03 266 0 2 8.33, 212 5 10.52 214 73

D CH3 C 13 H 20N 2 252.4 m/z, 0.44 274. 1.24 61.88, -CH2 A- CH3 03 252 5 3 7.99, 234 6 11.10 77 236

[042] Amino group protection of beta alanine by Boc anhydride

[043] To a solution of beta-alanine (0.89 g, 10 mmol) in triethyl amine (2 ml) and methanol (20 ml) was added Boc anhydride (3.2 g, 15 mmol) and mixture was stirred at 40 C for 6 hrs. After ter-butoxycarbonylation was complete (as evidenced by TLC using 3:1:0.5 hexane: ethyl acetate: methanol), stirring was continued for 30 min more, then the solvent was evaporated under reduced pressure and the residue was treated with ice-cold dilute HCl for 5 min and extracted immediately with Ethyl acetate. The organic layer was dried over magnesium sulphate, then filtered, and concentrated under vacuum.

[044] EXAMPLE 7: Synthesis of 3-Amino-N-[2-(3, 4-dihydroxy-phenyl)-ethyl] propionamide (DA-7)

[045] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15 mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-beta-alanine (1.89 g, 10 mmol).

After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10 mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether.

[046] Amino group protection of 6-amino caproic acid by Boc anhydrid

[047] To a solution of 6-amino caproic acid (1.31 g, 10 mmol) in triethyl amine (2 ml) and methanol (20 ml) was added Boc anhydride (3.2 g, 15 mmol) and mixture was stirred at 400 C for 6 hrs. After ter-butoxycarbonylation was complete (as evidenced by TLC using 3:1:0.5 hexane: ethyl acetate: methanol), stirring was continued for 30 min more, then the solvent was evaporated under reduced pressure and the residue was treated with ice-cold dilute hydrochloric acid for 5 min and extracted immediately with Ethyl acetate. The organic layer was dried over magnesium sulphate, then filtered, and concentrated under vacuum.

[048] EXAMPLE 8: Synthesis of 6-Amino-hexanoic acid [2-(3,4-dihydroxy-phenyl) ethyl]-amide (DA-8)

[049] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-6-amino caproic acid (2.31 g, mmol). After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether.

[050] Amino group protection of gama amino butyric acid by Boc anhydrid

[051] To a solution of gama amino butyric acid (10 mmol) intriethyl amine (2 ml) and methanol (20 ml) was added Boc anhydride (3.2 g, 15 mmol) and mixture was stirred at 40 C for 6 hrs. After ter-butoxycarbonylation was complete (as evidenced by TLC using 3:1:0.5 hexane: ethyl acetate: methanol), stirring was continued for 30 min more, then the solvent was evaporated under reduced pressure and the residue was treated with ice-cold dilute hydrochloric acid for 5 min and extracted immediately with ethyl acetate. The organic layer was dried over magnesium sulphate, then filtered, and concentrated under vacuum.

[052] EXAMPLE 9: Synthesis of 4-Amino-N-[2-(3, 4-dihydroxy-phenyl)-ethyl] butyramide (DA-9)

[053] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-gama amino butyric acid (1Ommol). After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether.

[054] Amino group protection of 5-amino pentanoic acid by Boc anhydrid

[055] To a solution of 5-amino pentanoic acid (1.17 g, 10 mmol) in triethyl amine (2 ml) and methanol (20 ml) was added Boc anhydride (3.2 g, 15 mmol) and mixture was stirred at 400 C for 6 hrs. After ter-butoxycarbonylation was complete (as evidenced by TLC using 3:1:0.5 hexane: ethyl acetate: methanol), stirring was continued for 30 min more, then the solvent was evaporated under reduced pressure and the residue was treated with ice-cold dilute hydrochloric acid for 5 min and extracted immediately with ethyl acetate. The organic layer was dried over magnesium sulphate, then filtered, and concentrated under vacuum.

[056] EXAMPLE 10: Synthesis of 5-Amino-pentanoic acid [2-(3, 4-dihydroxy-phenyl) ethyl]-amide (DA-10)

[057] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-5-amino pentanoic acid (2.17 g, 1Ommol). After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether.

[058] General structure of conjugates with increasing number of carbon chain between amino-carboxylic group.

HO 5 7 H 10 HO * r6N "r 'eNH 2 4 8

HO 3 0 2

[059] Table.2. Molecular Formula, Yield, Melting point, Rf, UV, Log P and Elemental analysis (%) (C, H, N)

Comps R Mol. Mol. Mass Rf UV log P Elemental formula weight Spectra Value Xmax Value analysis Yield obtained (%) (0%) Mp(0 C) (ESI MS) (C, H, N)

DA-7 - CiiH 16N2 0 3 224.25 m/z 224 0.46 285.5 0.671 58.91, CH2 - 7.19, 280 12.49 82 282

DA-8 - C 14 H 2 2N 2 0 3 266.33 [M+1]* 0.40 259.0 1.811 63.13, CH2 - m/z 267 8.33, 294 CH2 - 10.52 296 CH2 CH2

78

DA-9 CH2 - C 12 H1 iN 2 0 3 238.28 [M+1]* 0.38 272.5 1.110 60.49, CH2 - m/z 239 7.61,

80 266 11.76

DA-10 CH2 - C 13 H 20N 2 0 3 252.30 [M+1]* 0.41 265.5 1.405 61.88, CH2 - m/z 253 7.99, 214 CH2- 11.10 216 68

[060] Synthesis of phenylalanine methyl ester hydrochloride

[061] Added thionyl chloride (100 mmol, 7.43 ml) to 150 ml dry methanol drop wise with cooling (0 °C) in RBF, then added (100 mmol, 16.5 g) of phenylalanine to this solution. Reflux the solution for 4 hours. After cooling apply vacuum to get crude methyl ester hydrochloride. Triturate it with small portion of ether at 0 °C. Recrystallise from 25 ml of hot methanol by slow addition of ether followed by cooling to 0 °C. Yield-90 %, m.p.-195-200 0 C

[062] Synthesis of Boc-Phe-phe

[063] Phenylalanine methyl ester hydrochloride (10 mmol) was dissolved in Dichloromethane (20 ml). To this, triethyl amine (TEA) (2.8 ml, 0.021 mol) was added at °C and the reaction mixture was stirred for 15 min. Boc-phenyl alanine (10 mmol) in dichloromethane (20 ml) and N,N'-Dicyclohexylcarbodiimide (3.09 g, 15 mmol) were added with stirring. After 24 h, the reaction mixture was filtered and the residue was washed with dichloromethane (30 ml) and added to the filtrate. The filtrate was washed three times with 5% sodium bi carbonate and saturated sodium chloride solutions. The organic layer was dried over anhydrous sodium sulphate, filtered and evaporated in vacuum. The crude product was recrystallized from petroleum ether followed by cooling at 0 °C. Boc-phe-phe methyl ester hydrochloride was dissolved in methanol (20ml), and then added 1 N sodium hydroxide solution in excess. The solution was stirred until completed by TLC (usually 6 hr.). After that diluted hydrochloric acid was added until the mixture was neutral and precipitate was collected for further reaction.

[064] EXAMPLE 11: Synthesis of2-Amino-N-[1-{2-(3, 4-dihydroxy-phenyl)-ethyl carbamoyl}-2-phenyl-ethyl]-3-phenyl-popionamide (DA-11)

[065] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-Phe-phe (10mmol). After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether.

[066] Synthesis of leucine methyl ester hydrochloride

[067] Added thionyl chloride (100 mmol, 7.43 ml) to 150 ml dry methanol drop wise with cooling (0 °C) in RBF, then added (100 mmol, 13.1 g) of leucine to this solution. Reflux the solution for 4 hours. After cooling apply vacuum to get crude methyl ester hydrochloride. Triturate it with small portion of ether at 0 °C. Recrystallise from 25 ml of hot methanol by slow addition of ether followed by cooling to 0 °C. Yield-90 %, m.p.-165-170 0 C

[068] Synthesis of Boc-Phe-leu

[069] Leucine methyl ester hydrochloride (10 mmol) was dissolved in Dichloromethane (20 ml). To this, triethyl amine (TEA) (2.8 ml, 0.021 mol) was added at 0 °C and the reaction mixture was stirred for 15 min. Boc-phenyl alanine (10 mmol) in Dichloromethane (20 ml) and N,N'-Dicyclohexylcarbodiimide (3.09 g, 15 mmol) were added with stirring. After 24 h, the reaction mixture was filtered and the residue was washed with dichloromethane (30 ml) and added to the filtrate. The filtrate was washed three times with 5% sodium bi carbonate and saturated sodium chloride solutions. The organic layer was dried over anhydrous sodium sulphate, filtered and evaporated in vacuum. The crude product was recrystallized from petroleum ether followed by cooling at 0 °C. Boc-phe-leu methyl ester hydrochloride was dissolved in methanol (20ml), and then added 1 N Sodium hydroxide in excess. The solution was stirred until completed by TLC (usually 6 hr.). After this diluted hydrochloric acid was added until the mixture was neutral and precipitate was collected for further reaction.

[070] EXAMPLE 12: Synthesis of 2-(2-Amino-3-phenyl-propionyl amino)-4-methyl- pentanoic acid [2-(3,4-dihydroxy-phenyl)-ethyl]-amide (DA-12)

[071] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-Phe-leu (10mmol). After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether.

[072] Synthesis of leucine methyl ester hydrochloride

[073] Added thionyl chloride (100 mmol, 7.43 ml) to 150 ml dry methanol drop wise with cooling (0 °C) in RBF, then added (100 mmol, 13.1 g) of leucine to this solution. Reflux the solution for 4 hours. After cooling apply vacuum to get crude methyl °C. Recrystallise from 25 ester hydrochloride. Triturate it with small portion of ether at 0 ml of hot methanol by slow addition of ether followed by cooling to 0 °C. Yield-90 %, m.p.-165-170 0 C

[074] Synthesis of Boc-Ala-leu

[075] Leucine methyl ester hydrochloride (10 mmol) was dissolved in Dichloromethane (20 ml). To this, TEA (2.8 ml, 0.021 mol) was added at 0 °C and the reaction mixture was stirred for 15 min. Boc-phenyl alanine (10 mmol) in Dichloromethane (20 ml) and N,N' Dicyclohexylcarbodiimide (3.09 g, 15 mmol) were added with stirring. After 24 h, the reaction mixture was filtered and the residue was washed with Dichloromethane (30 ml) and added to the filtrate. The filtrate was washed three times with 5% sodium bi carbonate and saturated sodium chloride solutions. The organic layer was dried over anhydrous sodium sulphate, filtered and evaporated in vacuum. The crude product was recrystallized from petroleum ether followed by cooling at 0 °C. Boc-ala-leu methyl ester hydrochloride was dissolved in methanol (20ml), and then added 1 N sodium hydroxide in excess. The solution was stirred until completed by TLC (usually 6 hr.). After this diluted hydrochloric acid was added until the mixture was neutral and precipitate was collected for further reaction.

[076] EXAMPLE 12:

[077] Synthesis of 2-(2-Amino-propionyl amino)-4-methyl-pentanoic acid [2-(3,4 dihydroxy-phenyl)-ethyl]-amide (DA-13)

[078] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-ala-leu (10mmol). After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether.

[079] Synthesis of Valine methyl ester hydrochloride

[080] Added thionyl chloride (100 mmol, 7.43 ml) to 150 ml dry methanol drop wise with cooling (0 °C) in RBF, then added (100 mmol, 13.1 g) of Valine to this solution. Reflux the solution for 4 hours. After cooling apply vacuum to get crude methyl ester hydrochloride. Triturate it with small portion of ether at 0 °C. Recrystallise from 25 ml of hot methanol by slow addition of ether followed by cooling to 0 °C. Yield-90 %, m.p.-163-167 0 C

[081] Synthesis ofBoc-isoleu-val

[082] Valine methyl ester hydrochloride (10 mmol) was dissolved in Dichloromethane (20 ml). To this, TEA (2.8 ml, 0.021 mol) was added at 0 °C and the reaction mixture was stirred for 15 min. Boc-phenyl alanine (10 mmol) in dichloromethane (20 ml) and N,N' Dicyclohexylcarbodiimide (3.09 g, 15 mmol) were added with stirring. After 24 h, the reaction mixture was filtered and the residue was washed with dichloromethane (30 ml) and added to the filtrate. The filtrate was washed three times with 5% sodium bi carbonate and saturated sodium chloride solutions. The organic layer was dried over anhydrous sodium sulphate, filtered and evaporated in vacuum. The crude product was recrystallized from petroleum ether followed by cooling at 0 °C. Boc-isoleu-val methyl ester hydrochloride was dissolved in methanol (20ml) and then added 1 N sodium hydroxide in excess. The solution was stirred until completed by TLC (usually 6 hr.). After this diluted hydrochloric acid was added until the mixture was neutral and precipitate was collected for further reaction.

[083] EXAMPLE13: Synthesis of 2-Amino-3-methyl-pentanoic acid {1-[2-(3, 4- dihydroxy-phenyl)-ethyl carbamoyl]-2-methyl-propyl}-amide (DA-14)

[084] N, N'-Dicyclohexylcarbodiimide (3.09 g, 15mmol) was added to a stirred mixture of minimum quantity of pyridine solution at 0°C of Boc-isoleu-valine (10mmol). After a period of 15 min. the reaction mixture was admixed with the pyridine solution containing dopamine hydrochloride (1.89 g, 10mmol). The combined mixture was left stirred at room temperature for 24 h, the precipitated dicylohexylurea (DCU) was filtered and the organic extract was evaporated in vacuum. The residue was recrystallized from diethyl ether

R 0 5 7 H HO N 10 N 12 NH 2 8 H 0 R' 2

[085] General structure of dipeptide conjugate of Dopamine.

[086] Table.3 Molecular Formula, Yield, Melting point, Rf, UV, Log P and Elemental analysis (%) (C, H, N)

DA-11 R=- C 2 6H 2 9 N 3 0 4 447.52 m/z= 0.48 288.0 1.819 69.78, CH2 - 447 6.53,9.39 312 C 6H 5 314 R'= -

CH2

C6H 5

73

DA-12 R= - C 2 3 H3 1N 3 0 4 252.4 m/z= 0.44 274.5 1.668 66.81,7.56, CH2 - 252 10.16 334 C3H 7 336 R'=

CH2

C6H 5

77

DA-13 R= - C 17 H2 7N 3 0 4 337.4 [M+1]* 0.44 274.5 1.207 60.51, CH2 - m/z 338 8.07, 12.45 304 C3H 7 306 R'=

CH3

80

DA-14 R= - C 19H 3 1N 3 0 4 365.4 [M+1]* 0.44 274.5 1.098 62.44, C3 H 7 m/z 366 8.55,11.50 346 R'= - 348 C4 H 9

85

[087] While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

Claims

1. A method for synthesis of compounds comprising amino acids and peptide conjugated to dopamine for Parkinson's disorder.

2. The method as claimed in claim 1, wherein the synthesis of compounds amino acids and peptide conjugates of dopamine are synthesized by conventional phase solubility studies.

3. The compound as claimed in claim 1, wherein the compound has the formula: (i) 2-Amino-N-[2-(3, 4-dihydroxy-phenyl)-ethyl]-propionamide; (ii) 2-Amino-N-[2-(3, 4-dihydroxy-phenyl)-ethyl]-acetamide; (iii) 2-Amino-N-[2-(3,4-dihydroxy-phenyl)-ethyl]-3-phenyl-propionamide; (iv) 2-Amino-N-[2-(3,4-dihydroxy-phenyl)-ethyl]-3-(1H-indol-3-yl) propionamide; (v) 2-Amino-3-methyl-pentanoic acid [2-(3, 4-dihydroxy-phenyl)-ethyl] amide; (vi) 2-Amino-N-[2-(3,4-dihydroxy-phenyl)-ethyl]-3-methyl-butyramide; (vii) 3-Amino-N-[2-(3, 4-dihydroxy-phenyl)-ethyl]-propionamide; (viii) 6-Amino-hexanoic acid [2-(3,4-dihydroxy-phenyl)-ethyl]-amide; (ix) 4-Amino-N-[2-(3, 4-dihydroxy-phenyl)-ethyl]-butyramide; (x) 5-Amino-pentanoic acid [2-(3,4-dihydroxy-phenyl)-ethyl]-amide; (xi) 2-Amino-N-[1-{2-(3, 4-dihydroxy-phenyl)-ethyl carbamoyl}-2-phenyl ethyl]-3-phenyl-popionamide; (xii) 2-(2-Amino-3-phenyl-propionyl amino)-4-methyl-pentanoic acid [2-(3,4 dihydroxy-phenyl)-ethyl]-amide; (xiii) 2-(2-Amino-propionyl amino)-4-methyl-pentanoic acid [2-(3,4 dihydroxy-phenyl)-ethyl]-amide; and (xiv) 2-Amino-3-methyl-pentanoic acid {1-[2-(3, 4-dihydroxy-phenyl)-ethyl carbamoyl]-2-methyl-propyl}-amide.