Patent ID: 8846709

Claim:
A compound of formula (I) or a salt thereof wherein: R 1 is hydrogen or C 1-3 alkyl and R 2 is selected from hydrogen; C 1-6 alkyl; and C 2-6 alkyl substituted by hydroxy, C 1-4 alkoxy or a group NR a R b in which R a and R b are independently hydrogen or C 1-4 alkyl, or R a and R b combine together with the N to which they are attached to form a heterocyclyl ring; or R 1 and R 2 combine together with the N to which they are attached to form a heterocyclyl ring; R 3 is hydrogen, C 1-3 alkyl or CH 2 OH; R 4 is selected from a phenyl group optionally substituted by C 1-4 alkyl, CF 3 , halogen, hydroxy or C 1-4 alkoxy; a heteroaromatic group optionally substituted by C 1-4 alkyl, CF 3 , halogen, hydroxy or C 1-4 alkoxy; a tetrahydropyranyl group; a tetrahydrofuranyl group; a C 3-7 cycloalkyl group; and —CH 2 OMe.