Triazole-Based Thiamine Analogues as Inhibitors of Thiamine Pyrophosphate-Dependent Enzymes: 1,3-Dicarboxylate for Metal Binding

Thiamine 1 (vitamin B1) is essential for energy metabolism, and interruption of its utilisation pathways is linked to different disease states. Thiamine pyrophosphate 2a (TPP, the bioactive form of 1) functions as a coenzyme of a variety of enzymes. To understand the role of vitamin B1 in these diseases, a chemical approach is to use coenzyme analogues to compete with TPP for the enzyme active site, abolishing the coenzyme function. Exemplified by oxythiamine 3a and triazole hydroxamate 4, chemical probes require the coenzyme analogues to be membrane-permeable and of broad inhibitory activity to the enzyme family (rather than being too selective to particular TPP-dependent enzymes). In this study, using biochemical assays, we show that changing the hydroxamate metal-binding group of 4 to a 1,3-dicarboxylate moiety leads to potent inhibition of multiple TPP-dependent enzymes. We further demonstrate that this di-anionic thiamine analogue when masked in its diester form becomes membrane-permeable and can be unmasked by esterase treatment. Taken together, our inhibitors are potentially useful chemical tools to study the roles of vitamin B1, using a prodrug mechanism, to induce the effects of thiamine deficiency in cell-based assays.