Design, synthesis, and evaluation of 2 beta-alkenyl penam sulfone acids as inhibitors of beta-lactamases

Studies on enmetazobactam clarify mechanisms of widely used β-lactamase inhibitors

β-Lactams are the most important class of antibacterials, but their use is increasingly compromised by resistance, most importantly via serine β-lactamase (SBL)-catalyzed hydrolysis. The scope of β-lactam antibacterial activity can be substantially extended by coadministration with a penicillin-derived SBL inhibitor (SBLi), i.e., the penam sulfones tazobactam and sulbactam, which are mechanism-based inhibitors working by acylation of the nucleophilic serine. The new SBLi enmetazobactam, an N-methylated tazobactam derivative, has recently completed clinical trials. Biophysical studies on the mechanism of SBL inhibition by enmetazobactam reveal that it inhibits representatives of all SBL classes without undergoing substantial scaffold fragmentation, a finding that contrasts with previous reports on SBL inhibition by tazobactam and sulbactam. We therefore reinvestigated the mechanisms of tazobactam and sulbactam using mass spectrometry under denaturing and nondenaturing conditions, X-ray crystallography, and NMR spectroscopy. The results imply that the reported extensive fragmentation of penam sulfone–derived acyl–enzyme complexes does not substantially contribute to SBL inhibition. In addition to observation of previously identified inhibitor-induced SBL modifications, the results reveal that prolonged reaction of penam sulfones with SBLs can induce dehydration of the nucleophilic serine to give a dehydroalanine residue that undergoes reaction to give a previously unobserved lysinoalanine cross-link. The results clarify the mechanisms of action of widely clinically used SBLi, reveal limitations on the interpretation of mass spectrometry studies concerning mechanisms of SBLi, and will inform the development of new SBLi working by reaction to form hydrolytically stable acyl–enzyme complexes.

Palladium nanoparticles as efficient catalyst for C-S bond formation reactions

The development of green, economical and sustainable chemical processes is one of the primary challenges in organic synthesis. Herein, we report an efficient and heterogeneous palladium-catalyzed sulfonylation of vinyl cyclic carbonates with sodium sulfinates via decarboxylative cross-coupling. Both aliphatic and aromatic sulfinate salts react with various vinyl cyclic carbonates to deliver the desired allylic sulfones featuring tri- and even tetrasubstituted olefin scaffolds in high yields with excellent selectivity. The process needs only 2 mol% of Pd2(dba)3 and the in situ formed palladium nano-particles are found to be the active catalyst.

Photoinduced synthesis of allylic sulfones using potassium metabisulfite as the source of sulfur dioxide

Synthesis of allylic sulfones through a photoinduced three-component reaction of aryl/alkyl halides, potassium metabisulfite, and allylic bromides under ultraviolet irradiation at room temperature is developed. Diverse allylic sulfones are generated in moderate to good yields.

Allylic C-S Bond Construction through Metal-Free Direct Nitroalkene Sulfonation

A metal-free, open-flask protocol was developed for the preparation of allylic sulfones through direct condensation of sodium arylsulfinates and β,β-disubstituted nitroalkenes. The key step of this process was the Lewis base-promoted equilibrium between nitroalkenes and allylic nitro compounds. Through this process, the readily available conjugated nitroalkenes can be easily converted into allylic nitro compounds, which contain more reactive C═C bonds toward the sulfonyl radical addition. As a result, allylic sulfones were prepared in excellent yields with a broad substrate scope under mild conditions.

Chiral carbon–sulfur center formation via Pd-catalyzed asymmetric allylic thioetherification: synthesis of allylic thioethers

Pd-catalyzed asymmetric allylic thioetherification of various sodium thiolates was realized, giving the allylic thioethers with high enantioselectivity.

Synergistic antibacterial effects of herbal extracts and antibiotics on methicillin-resistant Staphylococcus aureus: A computational and experimental study

Antibiotic resistance has become a serious global concern, and the discovery of antimicrobial herbal constituents may provide valuable solutions to overcome the problem. In this study, the effects of therapies combining antibiotics and four medicinal herbs on methicillin-resistant Staphylococcus aureus (MRSA) were investigated. Specifically, the synergistic effects of Magnolia officinalis, Verbena officinalis, Momordica charantia, and Daphne genkwa in combination with oxacillin or gentamicin against methicillin-resistant (ATCC43300) and methicillin-susceptible (ATCC25923) S. aureus were examined. In vitro susceptibility and synergistic testing were performed to measure the minimum inhibitory concentration and fractional inhibitory concentration (FIC) index of the antibiotics and medicinal herbs against MRSA and methicillin-susceptible S. aureus. To identify the active constituents in producing these synergistic effects, in silico molecular docking was used to investigate the binding affinities of 139 constituents of the four herbs to the two common MRSA inhibitory targets, penicillin binding proteins 2a (PBP2a) and 4 (PBP4). The physicochemical and absorption, distribution, metabolism, and excretion properties and drug safety profiles of these compounds were also analyzed. D. genkwa extract potentiated the antibacterial effects of oxacillin against MRSA, as indicated by an FIC index value of 0.375. M. officinalis and V. officinalis produced partial synergistic effects when combined with oxacillin, whereas M. charantia was found to have no beneficial effects in inhibiting MRSA. Overall, tiliroside, pinoresinol, magnatriol B, and momorcharaside B were predicted to be PBP2a or PBP4 inhibitors with good drug-like properties. This study identifies compounds that deserve further investigation with the aim of developing therapeutic agents to modulate the effect of antibiotics on MRSA. Impact statement Antibiotic resistant is a well-known threat to global health and methicillin-resistant Staphylococcus aureus is one of the most significant ones. These resistant bacteria kill thousands of people every year and therefore a new effective antimicrobial treatment is necessary. This study identified the herbs and their associated bioactive ingredients that can potential the effects of current antibiotics. These herbs have long history of human usage in China and have well-defined monograph in the Chinese Pharmacopeia. These indicate their relatively high clinical safety and may have a quicker drug development process than that of a new novel antibiotic. Based on the results of this study, the authors will perform further in vitro and animal studies, aiming to accumulate significant data for the application of clinical trial.

Palladium-catalyzed allylation of sulfonyl hydrazides with alkynes to synthesize allylic arylsulfones

A novel method for the construction of allyl sulfone derivatives was developed by palladium catalyzed allylation of sulfony hydrazides with alkynes.

Synthesis, antibacterial activities, and 3D-QSAR of sulfone derivatives containing 1, 3, 4-oxadiazole moiety

A series of sulfone derivatives containing 1, 3, 4-oxadiazole moiety were prepared and evaluated for their antibacterial activities by the turbidimeter test. Most compounds inhibited growth of Ralstonia solanacearum (R. solanacearum) from tomato and tobacco bacterial wilt with high potency, among which compounds 5a and 5b exhibited the most potent inhibition against R. solanacearum from tomato and tobacco bacterial wilts with EC50 values of 19.77 and 8.29 μg/mL, respectively. Our results also demonstrated that 5a, 5b, and a number of other compounds were more potent than commercial bactericides Kocide 3000 and Thiodiazole Copper, which inhibited R. solanacearum from tomato bacterial wilt with EC50 values of 93.59 and 99.80 μg/mL and tobacco bacterial wilt with EC50 values of 45.91 and 216.70 μg/mL, respectively. The structure-activity relationship (SAR) of compounds was studied using three-dimensional quantitative structure-activity relationship (3D-QSAR) models created by comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) based on compound bioactivities against tomato and tobacco bacterial wilts. The 3D-QSAR models effectively predicted the correlation between inhibitory activity and steric-electrostatic properties of compounds.

Inhibition of tobacco bacterial wilt with sulfone derivatives containing an 1,3,4-oxadiazole moiety

A series of new sulfone compounds containing the 1,3,4-oxadiazole moiety were designed and synthesized. Their structures were identified by (1)H and (13)C nuclear magnetic resonance and elemental analyses. Antibacterial bioassays indicated that most compounds exhibited promising in vitro antibacterial bioactivities against tobacco bacterial wilt at 200 μg/mL. The relationship between structure and antibacterial activity was also discussed. Among the title compounds, 5'c, 5'h, 5'i, and 5'j could inhibit mycelia growth of Ralstonia solanacearum in vitro by approximately 50% (EC(50)) at 39.8, 60.3, 47.9, and 32.1 μg/mL, respectively. Among them, compound 5'j was identified as the most promising candidate due to its stronger effect than that of Kocide 3000 [Cu(OH)(2)] within the same concentration range. Field trials demonstrated that the control effect of compound 5'j against tobacco bacterial wilt was better than that of the commercial bactericide Saisentong. For the first time, the present work demonstrated that sulfone derivatives containing 1,3,4-oxadiazole can be used to develop potential bactericides for plants.

Carbon-sulfur bond formation via iridium-catalyzed asymmetric allylation of aliphatic thiols

An iridium-catalyzed regio- and enatioselective allylation with aliphatic thiols as the nucleophile in dichloromethane has been accomplished; and the branch products were obtained in 34-80% yields with up to 94/6 b/l and 98% ee.

Current challenges in antimicrobial chemotherapy: focus on ß-lactamase inhibition

The use of the three classical beta-lactamase inhibitors (clavulanic acid, tazobactam and sulbactam) in combination with beta-lactam antibacterials is currently the most successful strategy to combat beta-lactamase-mediated resistance. However, these inhibitors are efficient in inactivating only class A beta-lactamases and the efficiency of the inhibitor/antibacterial combination can be compromised by several mechanisms, such as the production of naturally resistant class B or class D enzymes, the hyperproduction of AmpC or even the production of evolved inhibitor-resistant class A enzymes. Thus, there is an urgent need for the development of novel inhibitors. For serine active enzymes (classes A, C and D), derivatives of the beta-lactam ring such as 6-beta-halogenopenicillanates, beta-lactam sulfones, penems and oxapenems, monobactams or trinems seem to be potential starting points to design efficient molecules (such as AM-112 and LK-157). Moreover, a promising non-beta-lactam molecule, NXL-104, is now under clinical development. In contrast, an ideal inhibitor of metallo-beta-lactamases (class B) remains to be found, despite the huge number of potential molecules already described (biphenyl tetrazoles, cysteinyl peptides, mercaptocarboxylates, succinic acid derivatives, etc.). The search for such an inhibitor is complicated by the absence of a covalent intermediate in their catalytic mechanisms and the fact that beta-lactam derivatives often behave as substrates rather than as inhibitors. Currently, the most promising broad-spectrum inhibitors of class B enzymes are molecules presenting chelating groups (thiols, carboxylates, etc.) combined with an aromatic group. This review describes all the types of molecules already tested as potential beta-lactamase inhibitors and thus constitutes an update of the current status in beta-lactamase inhibitor discovery.

Three decades of beta-lactamase inhibitors

Since the introduction of penicillin, beta-lactam antibiotics have been the antimicrobial agents of choice. Unfortunately, the efficacy of these life-saving antibiotics is significantly threatened by bacterial beta-lactamases. beta-Lactamases are now responsible for resistance to penicillins, extended-spectrum cephalosporins, monobactams, and carbapenems. In order to overcome beta-lactamase-mediated resistance, beta-lactamase inhibitors (clavulanate, sulbactam, and tazobactam) were introduced into clinical practice. These inhibitors greatly enhance the efficacy of their partner beta-lactams (amoxicillin, ampicillin, piperacillin, and ticarcillin) in the treatment of serious Enterobacteriaceae and penicillin-resistant staphylococcal infections. However, selective pressure from excess antibiotic use accelerated the emergence of resistance to beta-lactam-beta-lactamase inhibitor combinations. Furthermore, the prevalence of clinically relevant beta-lactamases from other classes that are resistant to inhibition is rapidly increasing. There is an urgent need for effective inhibitors that can restore the activity of beta-lactams. Here, we review the catalytic mechanisms of each beta-lactamase class. We then discuss approaches for circumventing beta-lactamase-mediated resistance, including properties and characteristics of mechanism-based inactivators. We next highlight the mechanisms of action and salient clinical and microbiological features of beta-lactamase inhibitors. We also emphasize their therapeutic applications. We close by focusing on novel compounds and the chemical features of these agents that may contribute to a "second generation" of inhibitors. The goal for the next 3 decades will be to design inhibitors that will be effective for more than a single class of beta-lactamases.

Inhibition of OXA-1 beta-lactamase by penems

The partnering of a beta-lactam with a beta-lactamase inhibitor is a highly effective strategy that can be used to combat bacterial resistance to beta-lactam antibiotics mediated by serine beta-lactamases (EC 3.2.5.6). To this end, we tested two novel penem inhibitors against OXA-1, a class D beta-lactamase that is resistant to inactivation by tazobactam. The K(i) of each penem inhibitor for OXA-1 was in the nM range (K(i) of penem 1, 45 +/- 8 nM; K(i) of penem 2, 12 +/- 2 nM). The first-order rate constant for enzyme and inhibitor complex inactivation of penems 1 and 2 for OXA-1 beta-lactamase were 0.13 +/- 0.01 s(-1) and 0.11 +/- 0.01 s(-1), respectively. By using an inhibitor-to-enzyme ratio of 1:1, 100% inactivation was achieved in <or=900 s and the recovery of OXA-1 beta-lactamase activity was not detected at 24 h. Covalent adducts of penems 1 and 2 (changes in molecular masses, +306 +/- 3 and +321 +/- 3 Da, respectively) were identified by electrospray ionization mass spectrometry (ESI-MS). After tryptic digestion of OXA-1 inactivated by penems 1 and 2, ESI-MS and matrix-assisted laser desorption ionization-time-of-flight MS identified the adducts of 306 +/- 3 and 321 +/- 3 Da attached to the peptide containing the active-site Ser67. The base hydrolysis of penem 2, monitored by serial (1)H nuclear magnetic resonance analysis, suggested that penem 2 formed a linear imine species that underwent 7-endo-trig cyclization to ultimately form a cyclic enamine, the 1,4-thiazepine derivative. Susceptibility testing demonstrated that the penem inhibitors at 4 mg/liter effectively restored susceptibility to piperacillin. Penem beta-lactamase inhibitors which demonstrate high affinities and which form long-lived acyl intermediates may prove to be extremely useful against the broad range of inhibitor-resistant serine beta-lactamases present in gram-negative bacteria.

Detection of plasmid-mediated class C β-lactamases

Plasmid-mediated class C beta-lactamases are reported from Enterobacteriaceae with increasing frequency. They likely originate from chromosomal AmpC of certain Gram-negative bacterial species and subsequently are mobilized onto transmissible plasmids. There are reports of unfavorable clinical outcomes in patients infected with these organisms and treated with broad-spectrum cephalosporins. However, unlike class A extended-spectrum beta-lactamases (ESBLs), no screening and confirmatory tests have been uniformly established for strains that produce class C beta-lactamases. Reduced susceptibility to cefoxitin is a sensitive but not specific indicator of class C beta-lactamase production. Simple confirmatory tests including tests using boronic acid compounds as specific class C beta-lactamase inhibitors have recently been developed. Their utilization will enable clinical microbiology laboratories to report those strains producing plasmid-mediated class C beta-lactamases as being resistant to all broad-spectrum cephalosporins, thus allowing physicians to prescribe appropriate antimicrobial therapy.

Inverse acyl phosph(on)ates: substrates or inhibitors of beta-lactam-recognizing enzymes?

Acyl phosph(on)ates represent a new class of inhibitors of beta-lactam-recognizing enzymes. Previously described members of this class were aroyl phosph(on)ates. These compounds have been shown to acylate and/or phosphylate the active site serine residue, leading to either transient or essentially irreversible inhibition [Li, N., and Pratt, R. F. (1998) J. Am. Chem. Soc.120, 4264-4268]. The present paper describes the synthesis and evaluation as inhibitors of an inverse pair of acyl phosph(on)ates that incorporate the amido side chain that represents a major substrate specificity determinant of these enzymes. Thus, N-(phenylacetyl)glycyl phenyl phosphate and benzoyl N-(benzyloxycarbonyl)aminomethyl phosphonate were prepared. The former of these compounds was found to be a substrate of typical class A and C beta-lactamases and of the DD-peptidase of Streptomyces R61; it thus acylates the active site serine. In contrast, the latter compound was an irreversible inhibitor of the above enzymes, probably by phosphonylation of the active site serine. With each of these enzymes therefore, the amido side chain rather than the acyl group dictates the orientation of the bound phosph(on)ate and thus the mode of reaction.

Understanding the longevity of the beta-lactam antibiotics and of antibiotic/beta-lactamase inhibitor combinations

Microbial resistance necessitates the search for new targets and new antibiotics. However, it is likely that resistance problems will eventually threaten these new products and it may, therefore, be instructive to review the successful employment of beta-lactam antibiotic/beta-lactamase inhibitor combinations to combat penicillin resistance. These combination drugs have proven successful for more than two decades, with inhibitor resistance still being relatively rare. The beta-lactamase inhibitors are mechanism-based irreversible inactivators. The ability of the inhibitors to avoid resistance may be due to the structural similarities between the substrate and inhibitor.

Evaluation of beta-lactamase inhibitors in disk tests for detection of plasmid-mediated AmpC beta-lactamases in well-characterized clinical strains of Klebsiella spp

The diagnostic utility of the AmpC beta-lactamase inhibitors LN-2-128, 48-1220, and Syn 2190 in combination with cefotetan (CTT) or cefoxitin in a disk test for the detection of clinical isolates of Klebsiella spp. producing plasmid-mediated AmpC beta-lactamases (pAmpCs) was evaluated. The combination of Syn 2190 and CTT had a sensitivity of 91%, a specificity of 100%, and a reproducibility of 100% and showed the best potential of using an inhibitor for detection of Klebsiella spp. producing pAmpCs.

Synthesis and biological evaluation of penam sulfones as inhibitors of β-lactamases

The chemical synthesis of a series of new penam sulfone derivatives bearing a 2beta-substituted-oxyimino and -hydrazone substituents, their beta-lactamase inhibitory properties against selected enzymes representing class A and C beta-lactamases are reported. The oxime containing penam sulfones strongly inhibited the Escherichia coli TEM-1 and Klebsiella pneumoniae cefotaximase (CTX-1) enzymes, but moderately inhibited the Pseudomonas aeruginosa 46012 cephalosporinase; while the 2beta-substituted-hydrazone derivatives were generally less active against these enzymes. Furthermore, most of the inhibitors enhanced the antibacterial activities of piperacillin (PIP) and ceftazidime (CAZ) particularly against TEM-1 and CTX-1 producing bacterial strains.

Use of beta-lactamase inhibitors in disk tests to detect plasmid-mediated AmpC beta-lactamases

Seeking a simple disk test for detection of organisms producing plasmid-mediated AmpC beta-lactamases, we evaluated the diagnostic utility of the beta-lactamase inhibitors 48-1220 (Ro 48-1220) and LN-2-128. Using NCCLS disk methodology, inhibition zone diameters were determined for five beta-lactam antibiotics tested alone and in combination with 20 microg of either 48-1220 or LN-2-128. Using an increase of > or =4 mm in zone diameter in the presence of an inhibitor as a positive test, cefotetan with LN-2-128 and 48-1220 was adequate for the detection of organisms producing plasmid-mediated AmpCs (specificity of 90% and sensitivity of 100%).

Tazobactam Forms a Stoichiometric trans-Enamine Intermediate in the E166A Variant of SHV-1 β-Lactamase: 1.63 Å Crystal Structure,

Many pathogenic bacteria develop antibiotic resistance by utilizing beta-lactamases to degrade penicillin-like antibiotics. A commonly prescribed mechanism-based inhibitor of beta-lactamases is tazobactam, which can function either irreversibly or in a transient manner. We have demonstrated previously that the reaction between tazobactam and a deacylation deficient variant of SHV-1 beta-lactamase, E166A, could be followed in single crystals using Raman microscopy [Helfand, M. S., et al. (2003) Biochemistry 42, 13386-13392]. The Raman data show that maximal populations of an enamine-like intermediate occur 20-30 min after "soaking in" has commenced. By flash-freezing crystals in this time frame, we were able to trap the enamine species. The resulting 1.63 A resolution crystal structure revealed tazobactam covalently bound in the trans-enamine intermediate state with close to 100% occupancy in the active site. The Raman data also indicated that tazobactam forms a larger population of enamine than sulbactam or clavulanic acid does and that tazobactam's intermediate is also the most long-lived. The crystal structure provides a rationale for this finding since only tazobactam is able to form favorable intra- and intermolecular interactions in the active site that stabilize this trans-enamine intermediate. These interactions involve both the sulfone and triazolyl groups that distinguish tazobactam from clavulanic acid and sulbactam, respectively. The observed stabilization of the transient intermediate of tazobactam is thought to contribute to tazobactam's superior in vitro and in vivo clinical efficacy. Understanding the structural details of differing inhibitor effectiveness can aid the design of improved mechanism-based beta-lactamase inhibitors.

Synthesis and biological evaluation of 6-bromo-6-substituted penicillanic acid derivatives as beta-lactamase inhibitors

The synthesis of a selected set of 6-bromopenicillanic acid derivatives with an additional C6 substituent is reported. All these substances were tested as inhibitors of class A and C beta-lactamase enzymes derived from Escherichia coli (TEM-1) and E. cloacae (P99). As 6-(1-hydroxyethyl) derivatives 4c and 6c were found to be weak beta-lactamase inhibitors, they were further investigated in combination with amoxicillin against a series of beta-lactamase-producing bacterial strains. Some structure-activity relationships are discussed.

Synthesis of cyclic sulfones by ring-closing metathesis

A general and highly efficient synthesis of cyclic sulfones based on ring-closing metathesis has been developed. The synthetic utility of the resulting cyclic sulfones was demonstrated by their participation in stereoselective Diels-Alder reactions and transformation to cyclic dienes by the Ramberg-Bäcklund reaction.

Inactivation of CMY-2 beta-lactamase by tazobactam: initial mass spectroscopic characterization

The CMY-2 beta-lactamase, a plasmid determined class C cephalosporinase, was shown to be susceptible to inhibition by tazobactam (K(i)=40 microM). The reaction product(s) of CMY-2 beta-lactamase with the beta-lactamase inhibitor tazobactam were analyzed by electrospray ionization/mass spectrometry (ESI/MS) to characterize the prominent intermediates of the inactivation pathway. The ESI/MS determined mass of CMY-2 beta-lactamase was 39851+/-3 Da. After inactivating CMY-2 beta-lactamase with excess tazobactam, a single species, M(r)=39931+/-3.0, was detected. Comparison of the peptide maps from tryptic digestion of the native enzyme and the inactivated beta-lactamase followed by LC/MS identified two 22 amino acid peptides containing the active site Ser64 modified by a fragment of tazobactam. These two peptides were increased in mass by 70 and 88 Da, respectively. UV difference spectra following inactivation revealed the presence of a new species with a 302 nm lambda(max). Based upon the increase in molecular mass of the tazobactam inactivated CMY-2 beta-lactamase, we propose that during the inactivation of this beta-lactamase by tazobactam an imine is formed. Tautomerization forms the spectrally observed enamine. Hydrolysis generates the covalently attached malonyl semialdehyde, its hydrate, or an enol. This work provides information on the mass of a stable enzyme intermediate of a class C beta-lactamase inactivated by tazobactam and, for the first time, unequivocal evidence that a cross-linked species is not required for apparent inactivation.

Overcoming antimicrobial resistance by targeting resistance mechanisms

Three mechanisms of antimicrobial resistance predominate in bacteria: antibiotic inactivation, target site modification, and altered uptake by way of restricted entry and/or enhanced efflux. Many of these involve enzymes or transport proteins whose activity can be targeted directly in an attemptto compromise resistance and, thus, potentiate antimicrobial activity. Alternatively, novel agents unaffected by these resistance mechanisms can be developed. Given the ongoing challenge posed by antimicrobial resistance in bacteria, targeting resistance in this way may be our best hope at prolonging the antibiotic era.

Outbreak of Klebsiella pneumoniae producing transferable AmpC-type beta-lactamase (ACC-1) originating from Hafnia alvei

Fifty-two strains of Klebsiella pneumoniae producing an AmpC-type plasmid-mediated beta-lactamase were isolated from 13 patients in the same intensive care unit between March 1998 and February 1999. These strains were resistant to ceftazidime, cefotaxime and ceftriaxone, but susceptible to cefoxitin, cefepime and aztreonam. Plasmid content and genomic DNA restriction pattern analysis suggested dissemination of a single clone. Two beta-lactamases were identified, TEM-1 and ACC-1. We used internal bla(ACC-1) primers, to sequence PCR products obtained from two unrelated strains of Hafnia alvei. Our results show that the ACC-1 beta-lactamase was derived from the chromosome-encoded AmpC-type enzyme of H. alvei.

Resisting resistance: new chemical strategies for battling superbugs

As microbes become increasingly resistant to antibiotics, and in many cases to several drugs simultaneously, the search is on to find new therapies. One method to combat resistance is to use inhibitors of resistance mechanisms to potentiate existing antibiotics. Recent efforts are encouraging and highlight the importance of research at the chemistry-microbiology interface in developing new approaches to tackle resistance.

Structure-based design guides the improved efficacy of deacylation transition state analogue inhibitors of TEM-1 beta-Lactamase(,)

Transition state analogue boronic acid inhibitors mimicking the structures and interactions of good penicillin substrates for the TEM-1 beta-lactamase of Escherchia coli were designed using graphic analyses based on the enzyme's 1.7 A crystallographic structure. The synthesis of two of these transition state analogues, (1R)-1-phenylacetamido-2-(3-carboxyphenyl)ethylboronic acid (1) and (1R)-1-acetamido-2-(3-carboxy-2-hydroxyphenyl)ethylboronic acid (2), is reported. Kinetic measurements show that, as designed, compounds 1 and 2 are highly effective deacylation transition state analogue inhibitors of TEM-1 beta-lactamase, with inhibition constants of 5.9 and 13 nM, respectively. These values identify them as among the most potent competitive inhibitors yet reported for a beta-lactamase. The best inhibitor of the current series was (1R)-1-phenylacetamido-2-(3-carboxyphenyl)ethylboronic acid (1, K(I) = 5.9 nM), which resembles most closely the best known substrate of TEM-1, benzylpenicillin (penicillin G). The high-resolution crystallographic structures of these two inhibitors covalently bound to TEM-1 are also described. In addition to verifying the design features, these two structures show interesting and unanticipated changes in the active site area, including strong hydrogen bond formation, water displacement, and rearrangement of side chains. The structures provide new insights into the further design of this potent class of beta-lactamase inhibitors.

b-Lactamase inhibitors

The use of beta-lactamase inhibitors in combination with a beta-lactamase-susceptible antibiotic is a useful strategy to rescue otherwise good antibiotics from failure. However, recent years have seen a rise in the numbers of beta-lactamases that are insensitive to the available beta-lactamase inhibitors. This review summarizes of the mechanisms of action of the principal types of inhibitors and the ways in which beta-lactamase are thought to develop resistance towards them. Ten general classes of inhibitors are reviewed, especially those of therapeutic importance (clavulanic acid, penam sulfones and carbapenems). Copyright 2000 Harcourt Publishers Ltd.

beta-Lactamase epidemiology and the utility of established and novel beta-lactamase inhibitors

beta-Lactamase inhibitor:beta-lactam combinations remain one of the most successful strategies for the treatment of bacterial infections. Over the last 20 years the number and diversity of serine and metallo active site beta-lactamases has increased dramatically. This review highlights some of the new additions to the beta-lactamase arena and discusses how the commercially available beta-lactamase inhibitors are keeping pace with the changing epidemiology of beta-lactamases. In addition, we survey the progress with the design of novel inhibitors of serine and metallo-beta-lactamases. Focus is given to the recent advances in the design of metallo-beta-lactamase inhibitors as these enzymes pose a serious emerging threat to the use of all beta-lactam based therapies.

A novel type of AmpC beta-lactamase, ACC-1, produced by a Klebsiella pneumoniae strain causing nosocomial pneumonia

A Klebsiella pneumoniae strain resistant to oxyimino cephalosporins was cultured from respiratory secretions of a patient suffering from nosocomial pneumonia in Kiel, Germany, in 1997. The isolate harbors a bla resistance gene located on a transmissible plasmid. An Escherichia coli transconjugant produces a beta-lactamase with an isoelectric point of 7.7 and a resistance phenotype characteristic of an AmpC (class 1) beta-lactamase except for low MICs of cephamycins. The bla gene was cloned and sequenced. It encodes a protein of 386 amino acids with the active site serine of the S-X-X-K motif at position 64, as is characteristic for class C beta-lactamases. Multiple alignment of the deduced amino acid sequence with 21 other AmpC beta-lactamases demonstrates only very distant homology, reaching at maximum 52.3% identity for the chromosomal AmpC beta-lactamase of Serratia marcescens SR50. The beta-lactamase of K. pneumoniae KUS represents a new type of AmpC-class enzyme, for which we propose the designation ACC-1 (Ambler class C-1).