Diamino variants of piperazine-based tissue transglutaminase inhibitors

[Display omitted] •First SAR study of piperazine core of most potent inhibitors of tissue transglutaminase (TG2).•kinact and KI values reported for each inhibitor, allowing for calibration against benchmark compounds.•S-2-methyl piperazine derivative more efficient than parent benchmark.•Cellular permeability shown to be excellent, and Pgp-mediated efflux is minimal, which bodes well for therapeutic potential. Tissue transglutaminase (TG2) is a multifunctional protein that can catalyze the cross-linking between proteins, and function as a G-protein. TG2’s unregulated behaviour has been associated with fibrosis, celiac disease and cancer metastasis. Recently, small molecule irreversible inhibitors have been designed, bearing an electrophilic warhead that can react with the catalytic cysteine, abolishing TG2’s catalytic and G-protein capabilities. Several research groups have converged on inhibitors comprising piperazine scaffolds, but no structure–activity relationships (SAR) of the piperazine core have been reported. In this study we synthesize a series of inhibitors with various diamino linkers, to understand what structural requirements are necessary for the core to help align the terminal acrylamide warhead in the optimal position. Kinetic evaluation using an in vitro biochemical assay provided the kinetic parameters kinact and KI for each inhibitor. This study revealed that adding a methyl group to the piperazine core can improve inhibitor efficiency.