Synthesis and structure-activity relationships of new cephalosporins with aminoimidazoles at C-7. Effect of the pKa of the C-7 aminoimidazole on antibacterial spectrum and .BETA.-lactamase stability.

Cephalosporins with new aminoimidazole heterocycles at C-7 have been synthesized by reaction of anti-alpha-aminooximes with C-7 dihaloisocyanocephalosporins esters or by direct condensation of 2-fluoroimidazoles with C-7 aminocephalosporins esters. These compounds combine a broad spectrum of antibacterial activity, including Gram-negative and Gram-positive organisms with a good beta-lactamase stability. Activity is discussed in terms of its relationship to the pKa of the C-7 aminoimidazole heterocycle, basic C-7 aminoimidazole residues gave cephalosporins with the best beta-lactamase stability but the poorest activity against Gram-positive organisms. An additional interesting property of the C-7 imidazolylaminocephalosporins is the oral activity present in some compounds of this series.