Toward development of selective DXP synthase inhibitors

Abstract

The methylerythritol phosphate (MEP) pathway for isoprenoid biosynthesis is essential in most human pathogens, including Mycobacterium tuberculosis and the malaria parasite Plasmodium falciparum. The first enzyme in this pathway, 1‐deoxy‐D‐xylulose 5‐phosphate (DXP) synthase, catalyzes the thiamin diphosphate (ThDP)‐dependent formation of DXP from D‐glyceraldehyde 3‐phosphate (GAP) and pyruvate. Selective inhibition of this ThDP‐dependent transformation is a challenging goal in the development of isoprenoid biosynthesis inhibitors. However, we have determined that DXP synthase follows a random sequential mechanism, distinguishing it mechanistically from other ThDP‐dependent enzymes; thus, we are pursuing it as a potential drug target for the development of new anti‐infective agents. We hypothesize that substrate specificity studies will guide the design of selective inhibitors of DXP synthase. We have utilized nitroso compounds as reactive aldehyde isosteres to investigate substrate specificity and have shown that DXP synthase catalyzes C‐N bond formation using nitroso acceptor substrates. Nitrosonaphthols show remarkably high affinity for DXP synthase as substrates, but low affinity for the related ThDP‐dependent enzyme, PDH. In contrast, these alternative substrates for DXP synthase are weak inhibitors of DXP formation, suggestive of distinct substrate and inhibitor binding modes for this compound class. Our results point to opportunities for development of naphthyl–containing inhibitors that target the unique mechanism of DXP synthase.