Patent ID: 8546612

Claim:
A process for the preparation of compounds of general formula (I) or pharmaceutically acceptable salts thereof, wherein R 1 is R 5 is hydrogen or hydroxy group; R 2 is hydrogen or amino group optionally substituted with CH 3 (CH 2 ) m CO—, where m is 0 to 4; R 3 is hydrogen, —COOH, —COOR 6 , where R 6 is C 1 -C 6 alkyl or where R 7 is hydrogen or a hydroxy group, R 4 is hydrogen, a hydroxy group; which comprises activation of a carboxyl group of a compound of general formula by reacting with diphenylphosphorylazide and triethylamine in an organic solvent at cooling, followed by reacting with an amino compound of general formula wherein R 1 -R 4 are as defined above.