Patent ID: 8133888

Claim:
Compounds of formula I or salts thereof, wherein, R 1 is selected from the group consisting of hydrogen and R 4 ; R 2 is selected from the group consisting of hydrogen, acetyl and R 4 ; R 3 is selected from the group consisting of alkyl, —O-alkyl, —NH-alkyl, aryl and heterocyclyl; R 4 represents a moiety (A) wherein, X is selected from the group consisting of a single bond, alkylene, alkenylene, alkynylene, arylene or a heterocyclylene moiety; R 5 and R 6 are same or different and are independently selected from hydrogen, alkyl, aryl or heterocyclyl; or R 5 and R 6 may form together with the nitrogen atom to which they are attached a heterocyclyl ring system.