>C???N--NH--R' (R' is acyl group), wherein R7 is a hydrogen atom, an alkyl group having 1-4 carbon atoms or --CH2 OR10 (where R10 is a hydrogen atom or an acyl group); Y is a simple bond or ##STR6## (where R11 is a hydrogen atom, an alkyl group having 1-4 carbon atoms or --CH2 OR14 (where R14 is a hydrogen atom or an acyl group), and R12 is a hydrogen atom or an alkyl group having 1-4 carbon atoms