Patent ID: 7935831

Claim:
A process for the preparation of compounds of the general formula (I) or their salts, wherein: R 1 is H, (C 1 -C 8 )-alkyl, (C 6 -C 18 )-aryl, (C 7 -C 19 )-aralkyl, (C 1 -C 8 )-alkyl-(C 6 -C 18 )-aryl, (C 3 -C 8 )-cycloalkyl, (C 1 -C 8 )-alkyl-(C 3 -C 8 )-cycloalkyl, (C 3 -C 8 )-cycloalkyl-(C 1 -C 8 )-alkyl, said process comprising hydrogenating a compound of general formula II in the presence of a catalyst: wherein R 1 is as described above and R 2 is a hydrogenolytically cleavable group.