IMP-1 metallo-␤-lactamase (class B) is a plasmid-borne zinc metalloenzyme that efficiently hydrolyzes ␤-lactam antibiotics, including carbapenems, rendering them ineffective. Because IMP-1 has been found in several clinically important carbapenem-resistant pathogens, there is a need for inhibitors of this enzyme that could protect broad spectrum antibiotics such as imipenem from hydrolysis and thus extend their utility. We have identified a series of 2,3-(S,S)-disubstituted succinic acids that are potent inhibitors of IMP-1. Determination of high resolution crystal structures and molecular modeling of succinic acid inhibitor complexes with IMP-1 has allowed an understanding of the potency, stereochemistry, and structure-activity relationships of these inhibitors.Carbapenems such as imipenem (Scheme 1) have proven useful for the treatment of a variety of Gram-negative and Gram-positive infections (1, 2). Carbapenems and other ␤-lactam antibiotics covalently modify penicillin-binding proteins (PBPs) 1 involved in the peptidoglycan biosynthetic pathway of cell wall assembly in bacteria (3, 4). Resistance to carbapenems can arise because of acquisition of low affinity PBPs (3) (e.g. PBP2a of Staphylococcus aureus), altered membrane permeability (5), and expression of class A, B, and D ␤-lactamases (6 -10). Class B ␤-lactamases (metallo-␤-lactamases or MBLs) can hydrolyze a wide variety of substrates of the ␤-lactam class, including carbapenems, penicillins, and cephalosporins, rendering them ineffective as antibiotics.The IMP-1 gene encoding an MBL has been identified on a plasmid and in Japan has transferred among clinical isolates such as Pseudomonas aeruginosa (11,12), Klebsiella pneumoniae, Serratia marcescens, and other members of the Enterobacteriaceae (13,14). In addition, carbapenem-resistant clinical isolates expressing MBLs related to IMP-1 have been identified recently in Singapore (15), Italy (16), and Hong Kong (10). Such reports of plasmid-borne imipenem resistance highlight the need for inhibitors of IMP-1 that can restore the activity of carbapenems in resistant bacteria.Several classes of MBL inhibitors have been reported (for reviews, see Refs. 17 and 18)) including phenazines (19), trifluoromethyl alcohol and ketone derivatives of L-and D-alanine (20), thioesters (18, 21-23), thiols (24 -28), biphenyl tetrazoles (29, 30), and amino acid-derived hydroxamates (31). Biphenyl tetrazoles have been shown to reverse imipenem resistance in a clinical isolate of Bacteroides fragilis (29), and thioesters have been shown to reverse resistance to the carbapenem L-742,728 in a laboratory strain of Escherichia coli expressing IMP-1 (32). A 1␤-methylcarbapenem substituted at C-2 with a benzothienylthio moiety has been reported to be a potent IMP-1 inhibitor that can reverse resistance to imipenem in an IMP-1-producing strain of Serratia marcescens (33). Although the inhibitors described above have been reported to have good activity against a specific MBL, only certain thiols (e.g. SB 264218) exhibit broad spe...

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The discovery and synthesis of dihydrobenzoxathiins as potent, ERalpha subtype selective ligands are described. The most active analogue, 4-D, was found to be 50-fold selective in a competitive binding assay and 100-fold selective in a transactivation assay in HEK-293 cells. The alpha selectivity was postulated to lie in the interaction of the sulfur atom of the benzoxathiin ring with the two discriminating residues in the binding pocket of the receptor isoforms.

Bacterial resistance to antibiotics continues to pose serious challenges as the discovery rate for new antibiotics fades. Kibdelomycin is one of the rare, novel, natural product antibiotics discovered recently that inhibits the bacterial DNA synthesis enzymes gyrase and topoisomerase IV. It is a broad-spectrum, Gram-positive antibiotic without cross-resistance to known gyrase inhibitors, including clinically effective quinolones. To understand its mechanism of action, binding mode, and lack of cross-resistance, we have co-crystallized kibdelomycin and novobiocin with the N-terminal domains of Staphylococcus aureus gyrase B (24 kDa) and topo IV (ParE, 24 and 43 kDa). Kibdelomycin shows a unique "dual-arm", U-shaped binding mode in both crystal structures. The pyrrolamide moiety in the lower part of kibdelomycin penetrates deeply into the ATP-binding site pocket, whereas the isopropyl-tetramic acid and sugar moiety of the upper part thoroughly engage in polar interactions with a surface patch of the protein. The isoproramic acid (1,3-dioxopyrrolidine) and a tetrahydropyran acetate group (Sugar A) make polar contact with a surface area consisting of helix α4 and the flexible loop connecting helices α3 and α4. The two arms are connected together by a rigid decalin linker that makes van del Waals contacts with the protein backbone. This "dual-arm", U-shaped, multicontact binding mode of kibdelomycin is unique and distinctively different from binding modes of other known gyrase inhibitors (e.g., coumarins and quinolones), which explains its lack of cross-resistance and low frequency of resistance. The crystal structures reported in this paper should enable design and discovery of analogues with better properties and antibacterial spectrum.

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