| 摘要 |
Cephem derivatives of the formula <IMAGE> in which R<1> is hydrogen or an alkyl group, X denotes oxygen or sulphur or a group of the formula =NR<2>, in which R<2> is hydrogen or an alkyl group and, in cases where R<2> is alkyl, this can form a ring with R<1>, Y denotes the acetoxy group or a group of the formula -SR<3>, in which R<3> is a nitrogen-containing heterocyclic group; and COOR represents a free or esterified carboxyl group, or pharmaceutically acceptable salts of these compounds, are prepared by reacting a compound of the formula <IMAGE> in which Y and COOR have the meaning indicated, or a salt of this compound with a carboxylic acid of the formula <IMAGE> in which R<1> and X have the meaning indicated, or with a reactive derivative of this carboxylic acid, if appropriate with intermediate protection of an imino group which is present. A resulting ester can be hydrolysed to the free carboxylic acid and a resulting free carboxylic acid can be converted into a pharmaceutically acceptable ester. The cephem derivatives of the formula I and their salts are antibiotics having a broad spectrum of action. They are also especially active against Gram-negative bacteria.
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