The expanding repertoire of covalent warheads for drug discovery

The reactive functionalities of drugs that engage in covalent interactions with the enzyme/receptor residue in either a reversible or an irreversible manner are called 'warheads'. Covalent warheads that were previously neglected because of safety concerns have recently gained center stage as a result of their various advantages over noncovalent drugs, including increased selectivity, increased residence time, and higher potency. With the approval of several covalent inhibitors over the past decade, research in this area has accelerated. Various strategies are being continuously developed to tune the characteristics of warheads to improve their potency and mitigate toxicity. Here, we review research progress in warhead discovery over the past 5 years to provide valuable insights for future drug discovery.

A structural metagenomics pipeline for examining the gut microbiome

Metagenomic sequencing data provide a rich resource from which to expand our understanding of differential protein functions involved in human health. Here, we outline a pipeline that combines microbial whole genome sequencing with protein structure data to yield a structural metagenomics-informed atlas of microbial enzyme families of interest. Visualizing metagenomics data through a structural lens facilitates downstream studies including targeted inhibition and probe-based proteomics to define at the molecular level how different enzyme orthologs impact in vivo function. Application of this pipeline to gut microbial enzymes like glucuronidases, TMA lyases, and bile salt hydrolases is expected to pinpoint their involvement in health and disease and may aid in the development of therapeutics that target specific enzymes within the microbiome.

3-Oxo-β-sultam as a Sulfonylating Chemotype for Inhibition of Serine Hydrolases and Activity-Based Protein Profiling

3-Oxo-β-sultams are four-membered ring ambident electrophiles that can react with nucleophiles either at the carbonyl carbon or at the sulfonyl sulfur atoms, and that have been reported to inhibit serine hydrolases via acylation of the active-site serine residue. We have developed a panel of 3-oxo-β-sultam inhibitors and show, through crystallographic data, that they are regioselective sulfonylating electrophiles, covalently binding to the catalytic serine of human and porcine elastases through the sulfur atom. Application of 3-oxo-β-sultam-derived activity-based probes in a human proteome revealed their potential to label disease-related serine hydrolases and proteasome subunits. Activity-based protein profiling applications of 3-oxo-β-sultams should open up new opportunities to investigate these classes of enzymes in complex proteomes and expand the toolbox of available sulfur-based covalent protein modifiers in chemical biology.

New Electrophiles and Strategies for Mechanism-Based and Targeted Covalent Inhibitor Design

Covalent inhibitors are experiencing a growing resurgence in drug design and are an increasingly useful tool in molecular biology. The ability to attach inhibitors to their targets by a covalent linkage offers pharmacodynamic and pharmacokinetic advantages, but this can also be a liability if undesired off-target reactions are not mitigated. The discovery of new electrophilic groups that react selectively with specific amino acid residues is therefore highly desirable in the design of targeted covalent inhibitors (TCIs). Additionally, the ability to control the reactivity through exploitation of the target enzyme's machinery, as in mechanism-based inhibitors (MBIs), greatly benefits from the discovery of new strategies. This Perspective showcases recent advances in electrophile development and their application in TCIs and MBIs, exhibiting high selectivity for their targets.

Covalent binders in drug discovery

Covalent modulation of protein function can have multiple utilities including therapeutics, and probes to interrogate biology. While this field is still viewed with scepticism due to the potential for (idiosyncratic) toxicities, significant strides have been made in terms of understanding how to tune electrophilicity to selectively target specific residues. Progress has also been made in harnessing the potential of covalent binders to uncover novel biology and to provide an enhanced utility as payloads for Antibody Drug Conjugates. This perspective covers the tenets and applications of covalent binders.

Synthesis of benzannelated sultams by intramolecular Pd-catalyzed arylation of tertiary sulfonamides

A new and efficient approach to five- and six-membered benzannelated sultams by intramolecular C-arylation of tertiary 1-(methoxycarbonyl)methanesulfonamides under palladium catalysis is described. In case of the α-toluenesulfonamide derivative, an unexpected formation of a 2,3-diarylindole was observed under the same conditions.

Activity-Based Protein Profiling in Bacteria

Understanding the molecular mechanisms of bacterial pathogenesis and virulence is of great importance from both an academic and clinical perspective, especially in view of an alarming increase in bacterial resistance to existing antibiotics and antibacterial agents. Use of small molecules to dissect the basis of these dynamic processes is a very attractive approach due to their ability for rapid spatiotemporal control of specific biochemical functions. Activity-based protein profiling (ABPP), employing small molecule probes to interrogate enzyme activities in complex proteomes, has emerged as a powerful tool to study bacterial pathogenesis. In this chapter, we present a set of ABPP methods to identify and analyze enzymes essential for growth, metabolism and virulence of different pathogens including S. aureus and L. monocytogenes using natural product-inspired activity-based probes.

Synthesis, conformation and antiproliferative activity of isothiazoloisoxazole 1,1-dioxides

Isothiazoles (I) reacted with 1,3-dipoles or NaN₃ to give cycloadducts (II) or thiazete (III). Thiazete (III) rearranged to give 1,2,3-oxathiazoline (IV).