1 10 alkyl ar or xar r 15 is independently hydrogen ar c 1 6 alkyl or xar r 16 is independently c 1 6 alkyl or phenyl substituted by one or more c 1 6 alkyl oh c 15 alkoxy s o q r 6 n r 6 2 br f i cl cf 3 or nhcor 6 x is independently ch 2 n o nr 6 or s o q x u2032 is independently o nr 6 or s o q y is independently ch 3 or x ch 2 n ar naphthyl indolyl pyridyl thienyl oxazolidinyl thiazolyl isothiazolyl pyrazolyl triazolyl tetrazolyl imidazolyl imidazolidinyl thiazolidinyl isoxazolyl oxadiazolyl thiadiazolyl morpholinyl piperidinyl piperazinyl pyrrolyl or pyrimidyl all of which may be unsubstituted or substituted by one or more z 1 or z 2 groups z 1 and z 2 are independently hydrogen xr 6 c 1 8 alkyl ch 2 q co 2 r 6 c o n r 6 2 cn ch 2 n oh no 2 f cl br i n r 6 2 nhc o r 6 o ch 2 m c o nr a so 2 r 16 ch 2 m oc o nr a so 2 r 16 o ch 2 m nr a c o nr a so 2 r 16 or tetrazolyl which may be substituted or unsubstituted by one or two c 1 6 alkyl cf 3 or c o r 6 provided r 3 r a and r 5 are not o u2014.