Patent ID: 7799810

Claim:
A compound of formula I wherein R 1 is C 1-3 alkyl; R 2 is phenyl, naphthyl or biphenylyl, each being optionally substituted by one or more substituents selected from halogen, SO 2 C 1-3 alkyl, acyl and a 5 or 6 membered heteroaryl; or an optionally substituted 5- or 6- membered heteroaryl; R 3 is H or C 1-3 alkyl; R 4 is phenyl, naphthyl or biphenylyl, each being optionally substituted by C 1-4 alkyl; or an optionally substituted 5- or 6- membered heteroaryl comprising at least one N as heteroatom; provided that R 4 is other than naphthyl when R 2 is phenyl substituted by and optionally halogen; and R 5 is H or C 1-3 alkyl; or a salt thereof.