Modifications of the C6-substituent of penicillin sulfones with the goal of improving inhibitor recognition and efficacy

Regio- and Stereoselective Intermolecular 1,2-Difunctionalization of Terminal Alkynes: An Approach to Access (Z)-β-Amidovinylsulfones

We have developed the first I2/base-catalyzed regio- and stereoselective intermolecular β-amidosulfonylation of terminal alkynes using sodium sulfinates and quinoxalinone derivatives. The present methodology is compatible with a broad spectrum of various heterocyclic amides, terminal alkynes, and sodium sulfinates. It provides rapid access to valuable (Z)-β-amidovinyl sulfones at mild conditions. Moreover, the synthetic application of this methodology was demonstrated by the late-stage functionalization of numerous bioactive molecules.

Metal- and Base-Free C(sp2)-H Arylsulfonylation of Enamides for Synthesis of (E)-β-Amidovinyl Sulfones via the Insertion of Sulfur Dioxide

A metal- and base-free C(sp²)-H direct arylsulfonylation of secondary and tertiary enamides with aryldiazonium salts and ex situ generated SO₂ (from SOgen) is presented. This method runs smoothly to produce β-amidovinyl sulfones with excellent stereoselectivities in moderate to excellent yields. Moreover, this strategy features good functional group tolerance and environmentally benign reaction conditions. Mechanistic experiments indicate that this sulfonylation may proceed in a radical pathway.

Protecting Groups in Peptide Synthesis

The protection of amino acid reactive functionalities including the α-amino group, the side chain (amines, carboxylic acids, alcohols, and thiols), or the carboxylic acid terminus is an essential strategy in peptide chemistry. This is mandatory to prevent polymerization of the amino acids and to minimize undesirable side reactions during the synthetic process. Proper protecting group manipulation strategies can maximize the yield of the desired product or allow the construction of complex peptide-based structures. Thus, the compatibility and orthogonality of each protecting group are key to achieve the proper control of molecular structure. Herein, we describe some common protecting groups and their general unmasking methods, in order to mask and expose amine, carboxylic acid, alcohol, and thiol functionalities to achieve the synthesis of peptides and related molecules.

Methods for Hydroxamic Acid Synthesis

Substituted hydroxamic acid is one of the most extensively studied pharmacophores because of their ability to chelate biologically important metal ions to modulate various enzymes, such as HDACs, urease, metallopeptidase, and carbonic anhydrase. Syntheses and biological studies of various classes of hydroxamic acid derivatives have been reported in numerous research articles in recent years but this is the first review article dedicated to their synthetic methods and their application for the synthesis of these novel molecules. In this review article, commercially available reagents and preparation of hydroxylamine donating reagents have also been described.

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.

Synthesis, characterization of penicillin G capped silver nanoconjugates to combat β-lactamase resistance in infectious microorganism

In the present study, a novel strategy was adopted to synthesize, β lactamase resistant penicillin G molecules by using the unique properties of silver nanoparticles. Ascorbic acid-stabilized spherical monodispersed silver nanoparticles were prepared by a simple chemical reaction. The formation processes of the silver nanoparticles were investigated by UV-vis spectroscopy and Atomic Force Microscopy (AFM). Free amine groups were introduced on the surface of native silver nanoparticles by coating a uniform layer of polyaniline and this was confirmed by FTIR spectroscopy and Scanning Electron Microscopy. Functionalized silver nanoparticles were then grafted to the C3 carboxyl group of the β lactam ring of penicillin G in the presence of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDAC) with a conjugation yield of 213 μg mg⁻¹. These novel silver penicillin G nanoconjugates showed a very good growth inhibition against both non-resistant Escherichia coli (gram negative) as well as toward β lactam resistant, E. coli (gram negative) and Staphylococcus aureus (gram positive).

Epidemiological expansion, structural studies, and clinical challenges of new β-lactamases from gram-negative bacteria

β-Lactamase evolution presents to the infectious disease community a major challenge in the treatment of infections caused by multidrug-resistant gram-negative bacteria. Because over 1,000 of these naturally occurring β-lactamases exist, attempts to correlate structure and function have become daunting. Although new enzymes in the extended-spectrum β-lactamase (ESBL) families are frequently identified, the older CTX-M-14 and CTX-M-15 enzymes have become the most prevalent ESBLs in global surveillance. Carbapenemases with either serine-based or zinc-facilitated hydrolysis mechanisms are posing some of the most critical problems. Most geographical regions now report KPC serine carbapenemases and the metallo-β-lactamases VIM, IMP, and NDM-1, even though NDM-1 was only recently identified. The rapid emergence of these newer enzymes, with multiple β-lactamases appearing in a single organism, makes the design of new β-lactamase inactivators or β-lactamase-stable β-lactams all the more difficult. Combination therapy will likely be required to counteract the continuing evolution of these insidious enzymes in multidrug-resistant pathogens.

Inactivation of a class A and a class C β-lactamase by 6β-(hydroxymethyl)penicillanic acid sulfone

β-Lactamase inhibitors (clavulanic acid, sulbactam, and tazobactam) contribute significantly to the longevity of the β-lactam antibiotics used to treat serious infections. In the quest to design more potent compounds and to understand the mechanism of action of known inhibitors, 6β-(hydroxymethyl)penicillanic acid sulfone (6β-HM-sulfone) was tested against isolates expressing the class A TEM-1 β-lactamase and a clinically important variant of the AmpC cephalosporinase of Pseudomonas aeruginosa, PDC-3. The addition of the 6β-HM-sulfone inhibitor to ampicillin was highly effective. 6β-HM-sulfone inhibited TEM-1 with an IC(50) of 12 ± 2 nM and PDC-3 with an IC(50) of 180 ± 36 nM, and displayed lower partition ratios than commercial inhibitors, with partition ratios (k(cat)/k(inact)) equal to 174 for TEM-1 and 4 for PDC-3. Measured for 20 h, 6β-HM-sulfone demonstrated rapid, first-order inactivation kinetics with the extent of inactivation being related to the concentration of inhibitor for both TEM-1 and PDC-3. Using mass spectrometry to gain insight into the intermediates of inactivation of this inhibitor, 6β-HM-sulfone was found to form a major adduct of +247 ± 5 Da with TEM-1 and +245 ± 5 Da with PDC-3, suggesting that the covalently bound, hydrolytically stabilized acyl-enzyme has lost a molecule of water (HOH). Minor adducts of +88 ± 5 Da with TEM-1 and +85 ± 5 Da with PDC-3 revealed that fragmentation of the covalent adduct can result but appeared to occur slowly with both enzymes. 6β-HM-sulfone is an effective and versatile β-lactamase inhibitor of representative class A and C enzymes.