5,5,6-Fused tricycles bearing imidazole and pyrazole 6-methylidene penems as broad-spectrum inhibitors of beta-lactamases.

Beta-lactamases are serine- and metal-dependent hydrolases, produced by the bacteria as defense against beta-lactam antibiotics. Commercially available inhibitors such as clavulanic acid, sulbactam, and tazobactam, which are currently used in the hospital settings, have reduced activity against newly emerging beta-lactamases. Bacterial production of diverse beta-lactamases including class-A, class-C, and ESBLs has motivated several research groups to search for inhibitors with a broader spectrum of activity. Previously, several novel 6-methylidene penems bearing, [5,5] [5,6] and [5,5,5] heterocycles have been synthesized in our laboratory and were shown to be potent and broad-spectrum beta-lactamase inhibitors. As a continuation of our previous work and in order to extend the structure-activity relationships, in this paper, we describe herein the synthesis and in vitro, in vivo activities of several novel 5,5,6-fused tricyclic heterocycles attached to the 6-methylidene penem core. The compounds presented in the current paper are potent and broad-spectrum inhibitors of the TEM-1 and AmpC beta-lactamases. In combination with piperacillin, their in vitro activities showed enhanced susceptibility to class A- and C-resistant strains studied in various bacteria. Some of the newly synthesized compounds such as 12a-c were shown to have in vivo activity in the acute lethal infection model against TEM-1 producing organisms. The 5,5,6-fused heterocyclic ring cores such as 21, 25, and 35 reported here are hitherto unknown in the literature.

Structure-activity relationship of 6-methylidene penems bearing 6,5 bicyclic heterocycles as broad-spectrum beta-lactamase inhibitors: evidence for 1,4-thiazepine intermediates with C7 R stereochemistry by computational methods.

The design and synthesis of a series of 6-methylidene penems containing [6,5]-fused bicycles (thiophene, imidazole, or pyrazle-fused system) as novel class A, B, and C beta-lactamase inhibitors is described. These penems proved to be potent inhibitors of the TEM-1 (class A) and AmpC (class C) beta-lactamases and less so against the class B metallo-beta-lactamase CcrA. Their in vitro and in vivo activities in combination with piperacillin are discussed. On the basis of the crystallographic structures of a serine-bound reaction intermediate of 2 with SHV-1 (class A) and GC1 (class C) enzymes, compounds 14a-l were designed and synthesized. Penems are proposed to form a seven-membered 1,4 thiazepine ring in both class A and C beta-lactamases. The interaction energy calculation for the enzyme-bound intermediates favor the formation of the C7 R enantiomer over the S enantiomer of the 1,4-thiazepine in both beta-lactamases, which is consistent with those obtained from the crystal structure of 2 with SHV-1 and GC1.