The present invention provides compounds of the general formula I and physiologically acceptable addition salts thereof: IN WHICH R1 represents a hydrogen atom or a lower alkyl group; R2 represents a hydrogen atom or a benzyl or benzhydryl group; R3 represents a hydrogen atom or a lower alkyl group or R3 represents an arylalkyl or aryloxyalkyl radical, which radicals may optionally be substituted by one or more alkoxy or hydroxyl groups; Z represents a group of formula -(CH2)nY in which n has the value of 0, 1 or 2, and Y represents a hydroxyl radical (except when n has the value O) or an alkoxycarbonyl group of the formula COOR where R represents a hydrogen atom or a lower alkyl group, or Y represents an amido group of formula CONR5R6 in which R5 and R6 are as defined below or a group of formula NR4CONR5R6, or -NR4SO2R7 (in which R4, R5 and R6, which may be the same or different, represent hydrogen atoms or lower alkyl groups and R7 represents a lower alkyl group) except where n O and Y NR4SO2R7, R4 is not hydrogen. Preferably at least one of the groups R1, R2 and R3 is other than hydrogen, particularly when Z represents a -COOR group.