| 摘要 |
A compound of the formula : <CHEM> in which R<1> is carboxy or protected carboxy, R<2> is hydroxy(lower)alkyl or protected hydroxy(lower)alkyl, R<3> is hydrogen or lower alkyl, R<4> is lower alkyl having suitable substituent(s), heterocyclic group optionally substituted by suitable substituent(s), or lower alkylsulfonyl, R<5> is hydrogen, lower alkanimidoyl or imino-protective group, A is lower alkylene, and X is sulfur, oxygen, imino or protected imino, provided that when X is oxygen, then R<4> is not "protected or unprotected ureido(lower)alkyl", and pharmaceutically acceptable salts thereof, processes for their preparation and pharmaceutical compositions comprising them as an active ingredient. The invention also relates to intermediates of the formula <CHEM> and a process for the preparation thereof. r |
