[Studies on the synthetic methods of 4-unsubstituted monocyclic beta-lactam antibiotics].

The key intermediate of monocyclic beta-lactams, N-benzyloxycarbonyl-3 S-amino-2-oxoazetidine(Ⅲ),was synthesized from L-( + )-2,3-diaminopropanoie acid(Ⅰ) by Ph_3P—(PyS)_2—CH_3CN system and N-benzyloxycarbonylation. Ⅰ was prepared from L(+)-aspartic acid by Schmidt rearrangement.Three derivatives(Ⅷa～c) of this monocyclic beta-lactam were prepared and their biological activities evaluated.