Oligopeptides and process for preparation thereof

A process for the preparation of compound of the formula (I) comprising the steps of:

• (i) reacting a compound selected from the group consisting of 9, 10 and 14 in a mixture of solvents THF/MeOH/H2O (3:1:1) with LiOH.H2O and stirring the mixture at a temperature in the range of 0° C. to 30° C., acidifying the resulting reaction mixture with 1N HCl, extracting the reaction mixture with ethyl acetate, washing with water and brine and concentrating in vacuum to obtain acid 38 from 9, 23 from 10 or 30 from 14;
• (ii) deprotecting of tert-Butyloxycarbonyl group by reacting the compound selected from a group consisting of 11, 12, and 17 in dichloromethane, with trifluoroacetic acid and stirring the mixture at a temperature in the range of 25° C. to 30° C., concentrating the reaction mixture under vacuum, followed by azeotroping with dichloromethane to obtain the trifluoroacetate salt 22, 37 or 47 from 11, 12 and 17 respectively;
• (iii) coupling of an acid compound selected from the group consisting of 23, 29 and 38 obtained in step (i) with TFA salt selected from the group consisting of 22, 37 and 47 obtained in step (ii) and 21 by sequential addition of HOBt and EDCI and DIPEA until reaction mixture is basic in a solvent dichloromethane or DMF at a temperature in the range of 0° C. to 5° C., followed by stirring at 25° C. to 30° C. for another period of 1 h to 12 h, diluting the the reaction mixture with a solvent followed by washing with 1N HCl solution, saturated NaHCO3 solution, water and brine, concentrating and purifying by standard chromatographic techniques to obtain the dipetides of formulae 34, 41, 50, 56, 61 or 65;
• (iv) deprotecting tert-Butyloxycarbonyl group of the dipeptides as obtained in step (iii) by the process as described in step (ii) to obtain trifluoroacetate salts 27, 29, 43, 52, 57, or 66;
• (v) reacting the acid 20 in dichloromethane and pyridine with a solution of DAST in dichloromethane via cannula, and stirring at 25° C. to 30° C. for the time ranging between 30 min to 1 hr, diluting with CH2Cl2, washing with ice-cold water, concentrating to obtain acid fluoride 25;
• (vi) deprotecting of tert-Butyloxycarbonyl group by the process as described in step (ii) by reacting the compound selected from a group consisting of compound 13, 15, and 16 to obtain the corresponding trifluoroacetate salts 24, 39 and 48;
• (vii) coupling the acid fluoride 25 obtained in step (v) with deprotected amino acids selected from the group of compounds obtained in step (vi) in the presence of DIPEA in a solvent dichloromethane or DMF at 0° C. to 5° C. followed by stirring at 25° C. to 30° C. for another period of 1 h to 12 h, diluting the reaction mixture with a solvent after stirring, washing with 1N HCl solution, saturated NaHCO3 solution, water and brine, concentrating and purifying by standard chromatographic techniques to obtain the dipeptides 33, 40 or 49;
• (viii) reacting the dipeptide compound selected from the group obtained in step (vii), by the process as described in step (i) to obtain acids 26, 42, or 51;
• (ix) coupling of an acid compound selected from group obtained in step (viii) with a trifluoroacetate salt selected from a group obtained in step (iv) by the process as described in step (iii) to obtain the tetrapetides 35, 44, 53 or 58;
• (x) deprotection of tert-Butyloxycarbonyl group as described in step (ii) by reacting the tetrapeptide compounds selected from step (ix) to obtain the trifluoroacetate salts 28, 45, 54 or 59;
• (xi) coupling of an acid compound selected from the group obtained in step (i) with a trifluoroacetate salt selected from the group obtained in step (iv) by the process as described in step (iii) to obtain the tripeptides 30 or 62;
• (xii) deprotecting of tert-Butyloxycarbonyl group by the process as described in step (ii) by reacting the compounds selected from the group consisting of tripeptide compounds obtained in step (xi) to obtain the trifluoroacetate salts 67 or 68;
• (xiii) coupling of an acid compound 20 with a deprotected tripetide selected from the group obtained in step (xii) by sequential addition of BOP-Cl and DIPEA until reaction mixture turns basic, in a solvent dichloromethane or DMF at 0° C. to 5° C. followed by stirring at 25° C. to 30° C. for another period of 1 h to 12 h, diluting the reaction mixture with a solvent after stirring, washing with 1N HCl solution, saturated NaHCO3 solution, water and brine, and concentrating and purifying by standard chromatographic techniques to provide the tetrapetides 32 or 69;
• (xiv) deprotecting of tert-Butyloxycarbonyl group by the process as described in step (ii) by reacting the compounds selected from the group consisting of tetrapeptide compounds obtained in step (xiii) to obtain the trifluoroacetate salts 63 or 70;
• (xv) coupling of an acid selected from 18 or 19 with a deprotected tetrapeptide selected from the group obtained in step (x) and (xiv) by sequential addition of HOBt and EDCI and DIPEA until reaction mixture turns basic in a solvent dichloromethane or DMF at 0° C. to 5° C. followed by stirring at 25° C. to 30° C. for another period of 1 h to 12 h, diluting the reaction mixture with a solvent after stirring, washing with 1N HCl solution, saturated NaHCO3 solution, water and brine, and concentrating and purifying by standard chromatographic techniques to obtain the Boc protected pentapetides 36, 46, 55, 60, 64 or 71 or compounds 2 or 4;
• (xvi) deprotecting of tert-Butyloxycarbonyl protected pentapetides 36, 46, 55, 60, 64, 71 obtained in step (xv) with trifluoroacetic acid in dichloromethane, at a temperature ranging between 0° C. to 30° C., for a period in the range of 30 minutes to 60 minutes, the reaction mixture was then concentrated in vacuum, followed by azeotroping with dichloromethane to obtain the trifluoroacetate salts i.e., compounds 1, 3, 5, 6, 7 or 8.