Direct introduction of a formamido group into the 7 alpha (6 alpha)-position of cephalosporins (penicillins).

A novel direct introduction of a formamido group into the 7 alpha (6 alpha)-position of cephalosporins (penicillins) was achieved by treatment of 7 beta (6 beta)-[(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1- ylidene)methylimino]cephem (penam) esters with N,N-bis(trimethylsilyl)formamide, followed by deblocking with Girard reagent T to give the corresponding 7 alpha (6 alpha)-formamido-7 beta (6 beta)-amino derivatives. Three 7 alpha-formamidocephalosporins were prepared by the conventional N-acylation of 7 alpha-formamidocephem. All of them were resistant to beta-lactamases, showing similar MIC values against both of a pair of a beta-lactamase-producing strain and the corresponding non or low-producing strain of the same species of bacteria, when tested on Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli, Proteus mirabilis, Proteus vulgaris, Morganella morganii, Enterobacter cloacae and Citrobacter freundii.