A compound of formula or a pharmaceutically acceptable salt, solvate or polymorph thereof, including all tautomers and stereoisomers thereof wherein: R 1 represents C 1-12 alkyl; C 2-12 alkenyl, wherein the double bond is not adjacent to the nitrogen; C 3-12 carbocyclyl; -C 1-6 alkyl- C 3-12 carbocyclyl; C 3-12 heterocyclyl; -C 1-6 alkyl- C 3-12 heterocyclyl; C 6-12 aryl; C 5-12 heteroaryl; -C 1-6 alkyl- C 6-12 aryl; -C 1-6 alkyl(C 6-12 aryl) 2; -C 1-6 alkyl-C 5-12 heteroaryl; -phenyl fused to C 3-12 carbocyclyl, -C 1-6 alkyl-(phenyl fused to C 3-12 carbocyclyl), -phenyl fused to C 3-12 heterocyclyl or -C 1-6 alkyl-(phenyl fused to C 3-12 heterocyclyl); in which any of the aforesaid C 3-12 carbocyclyl and C 3-12 heterocyclyl groups may optionally be substituted by one or more groups selected from methyl and oxo; and in which any of the aforesaid phenyl, C 6-12 aryl and C 5-12 heteroaryl groups may optionally be substituted by one or more substituents selected from C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 1-6 haloalkyl, -C 1-6 thioalkyl, -SO 2 C 1-4 alkyl, C 1-6 alkoxy-, -O-C 3 - 8 cycloalkyl, C 3-8 cycloalkyl, -SO 2 C 3-8 cycloalkyl, C 3-6 alkenyloxy-, C 3-6 alkynyloxy-, - C C 1-6 alkyl, C 1-6 alkoxy-C 1-6 alkyl-, nitro, halogen, cyano, hydroxyl, -C OH, -NH 2, - NHC 1-4 alkyl, -N(C 1-4 alkyl)(C 1-4 alkyl), -C N(C 1-4 alkyl)(C 1-4 alkyl), -C NH 2, -C NH(C 1-4 alkyl), - C OC 1-6 alkyl, -SOC 1-4 alkyl and -SOC 3-6 cycloalkyl; or R 1 represents phenyl substituted by phenyl, or phenyl substituted by a monocyclic C 5-12 heteroaryl group in which any of the aforesaid phenyl and monocyclic C 5-12 heteroaryl groups may optionally be substituted by one or more groups selected from C 1-4 alkyl, halogen and C 1-4 alkoxy; or R 1 represents phenyl substituted by benzyloxy- in which any of the aforesaid phenyl or benzyloxy groups may optionally be substituted on the ring by one or more groups selected from C 1-4 alkyl, halogen and C 1-4 alkoxy; and A represents wherein Z represents a bond, -CH 2 -, -CH 2 -CH 2 -, -CH(Me)-, -CH(Me)-CH 2 - or -CH 2 -CH(Me)- and R 5 and R 6 independently represent H or C 1-2 alkyl and B represents H or methyl; provided that the compound of formula is not: or R 1 represents C 1-12 alkyl; C 2-12 alkenyl, wherein the double bond is not adjacent to the nitrogen; C 3-12 carbocyclyl; -C 1-6 alkyl- C 3-12 carbocyclyl; C 3-12 heterocyclyl; -C 1-6 alkyl- C 3-12 heterocyclyl; C 6-12 aryl; C 5-12 heteroaryl; -C 1-6 alkyl- C 6-12 aryl; -C 1-6 alkyl(C 6-12 aryl) 2; -C 1-6 alkyl-C 5-12 heteroaryl; -phenyl fused to C 3-12 carbocyclyl, -C 1-6 alkyl-(phenyl fused to C 3-12 carbocyclyl), -phenyl fused to C 3-12 heterocyclyl or -C 1-6 alkyl-(phenyl fused to C 3-12 heterocyclyl); in which any of the aforesaid C 3-12 carbocyclyl and C 3-12 heterocyclyl groups may optionally be substituted by one or more groups selected from methyl and oxo; and in which any of the aforesaid phenyl, C 6-12 aryl and C 5-12 heteroaryl groups may optionally be substituted by one or more substituents selected from C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 1-6 haloalkyl, -C 1-6 thioalkyl, -SO 2 C 1-4 alkyl, C 1-6 alkoxy-, -O-C 3 - 8 cycloalkyl, C 3-8 cycloalkyl, -SO 2 C 3-8 cycloalkyl, C 3-6 alkenyloxy-, C 3-6 alkynyloxy-, - C C 1-6 alkyl, C 1-6 alkoxy-C 1-6 alkyl-, nitro, halogen, cyano, hydroxyl, -C OH, -NH 2, - NHC 1-4 alkyl, -N(C 1-4 alkyl)(C 1-4 alkyl), -C N(C 1-4 alkyl)(C 1-4 alkyl), -C NH 2, -C NH(C 1-4 alkyl), - C OC 1-6 alkyl, -SOC 1-4 alkyl and -SOC 3-6 cycloalkyl; or R 1 represents phenyl substituted by phenyl, or phenyl substituted by a monocyclic C 5-12 heteroaryl group in which any of the aforesaid phenyl and monocyclic C 5-12 heteroaryl groups may optionally be substituted by one or more groups selected from C 1-4 alkyl, halogen and C 1-4 alkoxy; or R 1 represents phenyl substituted by benzyloxy- in which any of the aforesaid phenyl or benzyloxy groups may optionally be substituted on the ring by one or more groups selected from C 1-4 alkyl, halogen and C 1-4 alkoxy; and A represents wherein Z represents a bond, -CH 2 -, -CH 2 -CH 2 -, -CH(Me)-, -CH(Me)-CH 2 - or -CH 2 -CH(Me)- and R 5 and R 6 independently represent H or C 1-2 alkyl and B represents H or methyl;