Inhibition of Thiamine Diphosphate (ThDP)-dependent Enzymes by Triazole-based Thiamine Analogues

Thiamine (vitamin B1) is metabolised into the coenzyme thiamine diphosphate (ThDP). Interrupting thiamine-utilisation leads to disease states and thiamine/ThDP analogues are commonly used as antagonists of thiamine-utilisation pathways to investigate the underlying pathophysiology. Oxythiamine, a thiamine analogue, uses the thiamine-utilising pathways for conversion into oxythiamine diphosphate (OxThDP), which binds to ThDP-dependent enzymes but lacks the catalytic activity of ThDP. Oxythiamine has been used to validate thiamine utilisation as an antimalarial drug target. However, high oxythiamine doses are often needed in vivo because 1) of its rapid clearance and 2) its potency decreases dramatically with thiamine levels. We report herein thiamine analogues possessing a triazole ring and a hydroxamate tail in place of the thiazolium ring and diphosphate group, respectively, of ThDP. We characterise their broad-spectrum inhibition of ThDP-dependent enzymes in biochemical and computational studies, and establish their ThDP-competitive action using Plasmodium falciparum as a model. We demonstrate how the cellular thiamine-utilisation pathway can be probed in mechanistic studies using our compounds and oxythiamine in parallel.