A compound of formula (I) or a pharmaceutically acceptable salt or in vivo hydrolysable ester thereof: IMAGE (I) wherein R1 is phenyl, 4-hydroxy phenyl, 3,4-dihydroxyphenyl, 3,4-diacetoxyphenyl or a 5- or 6- membered heterocyclic ring containing up to three heteroatoms selected from oxygen, sulphur or nitrogen, optionally substituted with hydroxy, amino, halogen or C1-6 alkoxy; and R2 is a sub-group of formula (A): -NH-R3 (A) wherein R3 is an optionally substituted C1-10 alkyl or C3-7 cycloalkyl group; or R2 is a sub-group of formula (B): -NH-CO-R4 (B) wherein R4 is an aryl group, an optionally substituted C1-10 alkyl group or a C1-6 alkyloxy group optionally substituted by an aryl group.
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