. . . . "ps being able to have one or more substituents) and a group of formula: COXR' in which X is an oxygen atom, a sulfur atom, or NZ (in which Z is a hydrogen atom or a lower alkyl group), and R' is an alkyl group, a cycloalkyl group, a substituted alkyl group, a substituted cycloalkyl group, an aryl group, or a substituted aryl group, and (b) when R is NH2, Y is a group of the formula: COXR' in which" .