cephem cephamycin 213.010 243.28000 Any member of the cephamycin sub-group of cephem antibiotics, differing from cephalosporins in possessing a methoxy group at the 7alpha-position of the cephem nucleus, and in being resistant to beta-lactamase. C8H7NO4SR2 CHEBI:55429 CO[C@]12SCC(C)=C(N1C(=O)[C@H]2C)C(O)=O PMID:1107228 cephamycins chebi_ontology