where R3 is a methyl or amino group, R4 is hydrogen or a C1-4 alkyl or alkoxy group, X is N or CR5 where R5 is hydrogen or halogen, and Y and Z are independently carbon or nitrogen atoms defining adjacent atoms of a five- to six-membered ring that is unsubstituted or substituted at one or more positions with oxo, halo, methyl or halomethyl groups.