Structure-activity relationships amongst beta-lactamase inhibitors

EnT-Mediated Amino-Sulfonylation of Alkenes with Bifunctional Sulfonamides: Access to β-Amino Sulfone Derivatives

β-Amino sulfones are commonly found structural motifs in biologically active compounds. Herein, we report a direct photocatalyzed amino-sulfonylation reaction of alkenes for the efficicient production of important compounds by simple hydrolysis without the need for additional oxidants and reductants. In this transformation, the sulfonamides worked as bifunctional reagents, simultaneously generating sulfonyl radicals and N-centered radicals which were added to alkene in a highly atom-economical fashion with high regioselectivity and diastereoselectivity. This approach showed high functional group tolerance and compatibility, facilitating the late-stage modification of some bioactive alkenes and sulfonamide molecules, thereby expanding the biologically relevant chemical space. Scaling up this reaction led to an efficient green synthesis of apremilast, one of the best-selling pharmceuticals, demonstrating the synthetic utility of the applied method. Moreover, mechanistic investigations suggest that an energy transfer (EnT) process was in operation.

Nickel-Catalyzed Highly Enantioselective Hydrogenation of β-Acetylamino Vinylsulfones: Access to Chiral β-Amido Sulfones

The nickel/( S)-Binapine complex was found to be an efficient catalyst for asymmetric hydrogenation of β-acetylamino vinylsulfones to afford chiral β-Amido sulfones with excellent yields and enantioselectivities (up to 95% yields and >99% ee). This protocol has good compatibility with a series of substituted ( Z)-β-acetylamino vinylsulfones or Z/ E isomeric mixtures. A gram-scale reaction has also been achieved in the presence of a 0.2 mol % catalyst loading.

Engineering the synthetic potential of β-lactam synthetase and the importance of catalytic loop dynamics

The 2-azetidinone ring of the Class A and D β-lactamase inhibitor clavulanic acid (1) is synthesized by the ATP-utilizing enzyme β-lactam synthetase (βLS). A hydroxyethyl group attached to C-6 of 1 in the (S) configuration markedly enhances the efficacy of this compound against Class C β-lactamases. Guided by a series of X-ray structures of βLS, we have engineered this enzyme to act upon a methylated substrate analogue to give selectively the (3S)-methyl β-lactam core, which, upon closure of the second ring of the bicyclic system of 1, would lead to the (6S)-methylated clavulanic acid derivative.

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 new C-6 alkyliden penicillin derivatives as beta-lactamase inhibitors

New penicillin, penicillin sulfone and sulfoxide derivatives bearing a C-6-alkyliden substituent were prepared. Their chemical synthesis, in vitro antibacterial activity and inhibition properties against two selected enzymes representing Class A and C beta-lactamases are reported. Compounds 3a-c, 7a-c were able to inhibit either TEM-1 (a Class A enzyme, from Escherichia coli) or P-99 (a Class C enzyme, from E. cloacae), or both enzymes, when tested in competition experiments using nitrocefin as the reporter substrate. However, when tested in combination with amoxicillin, the same compounds did not show synergistic effects against E. coli and E. cloacae strains producing TEM-1 and P99 enzymes, respectively. This finding is most likely related to poor penetration through the bacterial cell wall, as shown by using a more permeable isogenic E. coli strain. Interestingly, a synergistic effect against a strain of S. aureus which produces PC1-enzyme (a Class A beta-lactamase) was observed for compound 3a when used in combination with amoxicillin.

Kinetic and physical studies of beta-lactamase inhibition by a novel penem, BRL 42715

The interactions of Staphylococcus aureus, Bacillus cereus I, TEM, Klebsiella pneumoniae K1 and Enterobacter cloacae P99 beta-lactamases with the novel penem inhibitor BRL 42715 were investigated kinetically and, in some cases, by electrospray mass spectrometry (e.s.m.s.). All the beta-lactamases were rapidly inactivated by BRL 42715, with second-order rate constants ranging from 0.17 to 6.4 microM-1.s-1. The initial stoichiometry of beta-lactamase inhibition was essentially 1:1, with the exception of the K1 enzyme. In this instance about 20 molecules of BRL 42715 were hydrolysed before the enzyme was completely inhibited. Inhibited beta-lactamases did not readily regain activity in the absence of BRL 42715, the half-lives for regeneration of free enzyme ranging from 5 min for the K1 beta-lactamase to over 2 days for the staphylococcal enzyme. Recovery of activity was incomplete for TEM-1, K1 and P99 beta-lactamases, suggesting partitioning of the inhibited enzymes to give a permanently (or at least very stable) inactivated species. Examination of the interactions of the penem with TEM, B. cereus I and P99 beta-lactamases by e.s.m.s. also showed rapid and stoichiometric binding of the inhibitor. In all cases a mass increase of 264 Da over the native enzyme was observed, corresponding to the molecular mass of BRL 42715, showing that no fragmentation of the penem occurred on reaction with the beta-lactamases.

In vitro evaluation of BRL 42715, a novel beta-lactamase inhibitor

The penem BRL 42715, C6-(N1-methyl-1,2,3-triazolylmethylene)penem, is a potent inhibitor of a broad range of bacterial beta-lactamases, including the plasmid-mediated TEM, SHV, OXA, and staphylococcal enzymes, as well as the chromosomally mediated enzymes of Bacteroides, Enterobacter, Citrobacter, Serratia, Morganella, Escherichia, Klebsiella, and Proteus species. The concentration of BRL 42715 needed to reduce the initial rate of hydrolysis of most beta-lactamase enzymes by 50% was less than 0.01 micrograms/ml, which was 10- to 100-fold lower than for other beta-lactamase inhibitors. These potent inhibitory activities were reflected in the low concentrations of BRL 42715 needed to potentiate the antibacterial activity of beta-lactamase-susceptible beta-lactams. Concentrations of 0.25 micrograms/ml or less considerably enhanced the activity of amoxicillin against many beta-lactamase-producing strains. The MIC50 (MIC for 50% of strains tested) of amoxicillin for 412 beta-lactamase-producing members of the family Enterobacteriaceae fell from greater than 128 to 2 micrograms/ml in the presence of 1 microgram of BRL 42715 per ml, whereas 5 micrograms of clavulanic acid per ml brought the MIC50 down to 8 micrograms/ml. Among these 412 strains were 73 Citrobacter and Enterobacter strains, and 1 microgram of BRL 42715 per ml reduced the MIC50 of amoxicillin from greater than 128 to 2 micrograms/ml for the 48 cefotaxime-susceptible strains and from greater than 128 to 8 micrograms/ml for the 25 cefotaxime-resistant strains.

The potential use of mechanism-based enzyme inactivators in medicine

Mechanism-based enzyme inactivator, alanine racemase, S-adenosylhomocysteine hydrolase, D-amino acid aminotransferase, gamma-aminobutyric acid aminotransferase, arginine decarboxylase, aromatase, L-aromatic amino acid decarboxylase, dihydrofolate reductase, dihydroorotate dehydrogenase DNA polymerase I, dopamine beta-hydroxylase, histidine decarboxylase, beta-lactamase, monoamine oxidase, ornithine decarboxylase, serine proteases, testosterone 5 alpha-reductase, thymidylate synthetase, xanthine oxidase.