The development of new cephalosporins with improved activity against resistant microbes, such as, MRSA (methicillin resistant Staph. aureus), P. aeruginosa, is of high potential. Chemical synthesis of two new series of thiadiazole linked to cysteine (series 1) and cephalosporins containing thiadiazole linked to cysteine through disulfide bond (series 2) were achieved. The chemical structures of the synthesized compounds were confirmed using spectral (FT-IR, ¹H-NMR) and elemental microanalysis. The incorporation of privileged chemical moieties, such as, thiadiazole, Schiff base, cysteine and sulfonamide, has been found to have great contribution to the antimicrobial activities. Compounds of series 1 (1b-d), containing a Schiff base or a sulfonamido moiety, showed reasonable activity and were less potent than cephalexin with respect to E. coli and Staph. aureus. The new cephalosporins (series 2) showed remarkable activities on E. coli (62.5-15.6µg/ml) and staph. aureus (31.2-62.5µg/ml) when compared with cephalexin (250 and 125 µg/ml) respectively. Moreover, compounds 1 and 3 showed very promising activity against MRSA (250 and 500µg/ml) respectively. The incorporation of a sulfonamido moiety to the cephalosporin molecule was successfully achieved. This is a very interesting finding which may open a new approach in the synthesis of newer cephalosporins.   

Keywords: Cephalosporins, Cysteine, Schiff base, Sulfonamides, Thiadiazole.