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Cephems having the basic structure shown. See also cephams, cephems, penams, penems, penicillins.
Natural and synthetic antibiotics containing the 5-thia-1-azabicyclo[4.2.0]octan-8-one nucleus; generally assumed to have the 6R configuration, unless otherwise specified. The numbering used differs from that of the von Baeyer named bicyclic system. Where they differ, the von Baeyer numbering is shown in parentheses.
3,4-Didehydrocephams: 5-thia-1-azabicyclo[4.2.0]oct-2-en-8-ones. See cephalosporins, cephams. 
Natural and synthetic antibiotics containing the 4-thia-1-azabicyclo[3.2.0]heptan-7-one structure, generally assumed to have the 5R configuration unless otherwise specified. The numbering of the penam skeleton differs from that of the von Baeyer named bicyclic system. Where they differ the von Baeyer numbering is shown in parenthesis in the example. Cf. penems.
2,3-Didehydropenams. Cf. penams.
Substituted penams having the basic structure shown, including the natural penicillins and synthetic analogues.
A subclass of polyketides having an octahydrotetracene-2-carboxamide skeleton, substituted with many hydroxy and other groups. E.g.
chlortetracycline