SM-216601, a novel parenteral 1beta-methylcarbapenem: structure-activity relationships of antibacterial activity and neurotoxicity in mice.

It has been reported that 2-(4-substituted thiazol-2-ylthio)-1beta-methyl-carbapenems exhibit potent activity against methicillin-resistant staphylococci (MRS) and vancomycin-resistant enterococci (VRE). In order to develop a novel broad-spectrum carbapenem, the structure-activity relationships of a series of 2-(4-tetrahydropyridinylthiazol-2-ylthio)-1beta-methylcarbapenems and 4-dihydropyrrolyl thiazole analogs were investigated with regard to their activity against Gram-positive and especially Gram-negative bacteria and also their convulsant activity, which is a major side effect concern of carbapenems. The introduction of substituent(s) on the dihydropyrrole moiety did not cause remarkable changes in anti-MRS and VRE activities, but tended to lower the anti-Gram-negative bacterial activity except in some cases of methyl group introduction. These substitutions did however cause a reduction of the convulsant activity, which was affected by the size and also the configuration of the substituent. In the case of SM-216601 (6), introduction of a methyl group brought about significant reduction in neurotoxicity while maintaining favorable anti-Gram-negative bacterial activity.