Certain compounds of formula (I) below or a pharmaceutically acceptable salt or hydrate thereof: wherein: R1 is H or C1-6 alkyl; R2 is aryl or C3-7 cycloalkyl or heteroaryl; R3 is H or C1-3 alkyl, optionally substituted by one or more fluorines; R4 is R8R9; R8 is a single bond, C1-6 alkyl, or aryl; R9 is H, COO R10, or NR11R12; R10 is H or C1-6 alkyl; R11 and R12 are independently selected from H and C1-6 alkyl; R5 is branched or linear C1-6 alkyl, C3-7 cycloalkyl, C4-7 cycloalkylalkyl, aryl, or a single or fused ring aromatic heterocyclic group; R6 represents H or up to three substituents independently selected from the list consisting of: C1-6 alkyl, C1-6 alkenyl, aryl, C1-6 alkoxy, hydroxy, halogen, nitro, cyano, carboxy, carboxamido, sulphonamido, C1-6 alkoxycarbonyl, trifluoromethyl, acyloxy, amino or mono- or di-C1-6 alkylamino; R7 is H or halo; a is 1-6; and any of R2, R5, R8, R10, R11 and R12 may optionally be substituted one or more times by halo, hydroxy, amino, cyano, nitro, carboxy or oxo; a process for preparing such compounds, a pharmaceutical composition comprising such compounds and the use of such compounds and composition in medicine.