Irreversible Inhibition of IspG, a Target for the Development of New Antimicrobials, by a 2‐Vinyl Analogue of its MEcPP Substrate

IspG (also called GcpE) is an oxygen‐sensitive [4Fe‐4S] enzyme catalyzing the penultimate step of the methylerythritol phosphate (MEP) pathway, a validated target for drug development. It converts 2‐C‐methyl‐d‐erythritol‐2,4‐cyclo‐diphosphate (MEcPP) into (E)‐4‐hydroxy‐3‐methyl‐but‐2‐enyl‐1‐diphosphate (HMBPP). The reaction, assimilated to a reductive dehydration, involves redox partners responsible for the formal transfer of two electrons to substrate MEcPP. The 2‐vinyl analogue of MEcPP was designed to generate conjugated species during enzyme catalysis, with the aim of providing new reactive centers to be covalently trapped by neighboring amino acid residues. The synthesized substrate analogue displayed irreversible inhibition towards IspG. Furthermore, we have shown that electron transfer occurs prior to inhibition; this might designate conjugated intermediates as probable affinity tags through covalent interaction at the catalytic site. This is the first report of an irreversible inhibitor of the IspG metalloenzyme. A substrate analogue of MEcPP, a key intermediate in the MEP pathway, has been synthesized. The target compound features a vinyl functionality in place of the natural methyl substituent. Potent irreversible inhibition towards GcpE (IspG) was observed. Introduction of a double bond allows conjugation in the putative reactive intermediates while entering enzymatic transformation. Unexpected covalent trapping could happen as consequential damage.