The use of covalent irreversible binding inhibitors is an established concept for drug development. Usually the discovery of new irreversible kinase inhibitors occurs serendipitously showing that efficient rational approaches for the rapid discovery of new drugs are needed.Herein, we report a virtual screening strategy that led to the discovery of irreversible inhibitors of the FMS-like tyrosine kinase 3 (FLT3) involved in the pathogenesis of acute myeloid leukemia (AML). A virtual screening library was designed to target the highly conserved Cys828 residue preceding the DFG motif by modification of reported reversible inhibitors with chemically reactive groups. Prospective covalent docking allowed the identification of two lead series, resulting in a massive increase in inhibition of kinase activity and cell viability by irreversible inhibitors compared to the corresponding reversible scaffolds. Lead compound 4b (BSc5371) displays superior cytotoxicity in FLT3-dependent cell lines to compounds in recent clinical trials and overcomes drug-resistant mutations.

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An efficient three-step synthetic route to α-ketoaldehydes starting from aryl aldehydes is reported. The aldehydes were treated with iPrMgCl and iodoform to obtain β-diiodoalcohols, which were then oxidized with o-iodoxybenzoic acid at room temperature to the corresponding β-diiodoketones.

Activating mutations of FMS-like tyrosine kinase 3 (FLT3) are present in ∼30 % of patients with acute myeloid leukemia (AML) and are associated with poor prognosis. Point mutations in the tyrosine kinase domain (TKD) are observed as primary mutations or are acquired as secondary mutations in FLT3 with internal tandem duplications (ITDs) after treatment with tyrosine kinase inhibitors (TKIs). Although dozens of potent inhibitors against FLT3 ITD have been reported, activating TKD point mutations, especially at residues F691 and D835, remain the leading cause for therapy resistance, highlighting the consistent need for new potent inhibitors. Herein we report the identification and characterization of novel quinoxaline-based FLT3 inhibitors. We used the pharmacophore features of diverse known inhibitors as a starting point for a new optimization algorithm for type II TKIs, starting from an in silico library pharmacophore search and induced-fit docking in the known FLT3 structure. This led to the design of a set of diverse quinoxalinebisarylureas, which were profiled in an FLT3 kinase activity assay. The most promising compounds were further evaluated in a zebrafish embryo phenotype assay.

The ubiquitin/proteasome system is the major protein degradation pathway in eukaryotes with several key catalytic cores. Targeting the β5 subunit with small-molecule inhibitors is an established therapeutic strategy for hematologic cancers. Herein, we report a mouse-trap-like conformational change that influences molecular recognition depending on the substitution pattern of a bound ligand. Variation of the size of P1 residues from the highly β5-selective proteasome inhibitor BSc2118 allows for discrimination between inhibitory strength and substrate conversion. We found that increasing molecular size strengthens inhibition, whereas decreasing P1 size accelerates substrate conversion. Evaluation of substrate hydrolysis after silencing of β5 activity reveals significant residual activity for large residues exclusively. Thus, classification of the β5 subunit as chymotrypsin-like and the use of the standard tyrosine-containing substrate should be reconsidered.