Patent ID: 7220774

Claim:
A compound of formula I wherein R a is H; C 1-4 alkyl; or C 1-4 alkyl substituted by OH, NH 2 , NHC 1-4 alkyl or N(C 1-4 alkyl) 2 ; R b is H; or C 1-4 alkyl; R is a radical of formula (b) or (c), wherein each of R 4 and R 7 is OH; SH; NR 16 R 17 wherein each of R 16 and R 17 , independently, is H or C 1-4 alkyl or a radical of formula α —X—R c —Y (α) wherein X is a direct bond, O, S or NR 18 wherein R 18 is H or C 1-4 alkyl, R c is C 1-4 alkylene or C 1-4 alkylene wherein one CH 2 is replaced by CR x R y wherein one of R x and R y is H and the other is CH 3 , each of R x and R y is CH 3 or R x and R y form together —CH 2 —CH 2 —, and Y is bound to the terminal carbon atom and is selected from OH and —NR 19 R 20 wherein each of R 19 and R 20 independently is H, C 3-6 cycloalkyl, C 3-6 cycloalkyl-C 1-4 alkyl, aryl-C 1-4 alkyl or C 1-4 alkyl optionally substituted on the terminal carbon atom by OH, each of R 5 and R 6 , independently, is H, halogen, C 1-4 alkyl, CF 3 , OH, SH, NH 2 , C 1-4 alkoxy, C 1-4 alkylthio, NHC 1-4 alkyl, N(C 1-4 alkyl) 2 or CN; ring A is optionally substituted, or a salt thereof.