ethyl group or propyl group, or a heterocyclic group which is capable of forming a ring, involving an oxygen or nitrogen atom, together with Ra1 and Ra2 ; Aa2, Aa3 and Aa4 independently represent a hydrogen atom, or an alkyl group such as a methyl or ethyl group, or a halogen atom such as a chlorine, fluorine, or bromine atom; Aa1 represents a hydroxy group or ##STR191## additionally, Ra3 and Ra4