It is stated in GB 2044255 published Oct. 15, 1980 that the invention therein relates to hitherto unknown compounds of the general formula 1: ##STR12## in which R1 stands for a phenyl, 4-hydroxyphenyl, 1,4-cyclohexadienyl or a 3-thienyl group; R2 represents a primary amino or a carboxy group; R3 is a hydrogen atom, or a lower alkyl, aryl or aralkyl radical, and A stands for a radical of a ??-lacta