Cephalosporanic acids. Part IV. 7-Acylamidoceph-2-em-4-carboxylic acids
The combined action of bases and acid anhydrides on 7-acylamidocephalosporanic acids, and the action of bases on their esters, set up equilibria in which the corresponding Δ2-isomers predominate. The isomerisation represents a prototropic shift probably favoured by the sulphur atom in the dihydrothiazine ring. The acetoxy-group in the Δ2-compounds can be replaced by nucleophiles.
Treatment of methyl 3-acetoxymethyl-7β-phenylacetamidoceph-3-em-4-carboxylate 1ξ-oxide with a base results in decarboxylation. Attempts to prepare 7β-phenylacetamidoceph-2-em-4ξ-carboxylic acid 1ξ-oxide resulted in formation of its Δ3-isomer and some carbon dioxide.