# Substitution of CH3 by CH2F in 2‐Methylerythritol Cyclodiphosphate Triggers Potent Inhibition of IspG with Concomitant Fluoride Ion Expulsion

## TL;DR

A fluorinated compound inhibits a key enzyme in a microbial pathway, supporting a proposed reaction mechanism involving a carbanionic intermediate.

## Contribution

A fluoromethyl-substituted MEcPP analogue was synthesized and shown to potently inhibit IspG while releasing fluoride.

## Key findings

- The fluoromethyl MEcPP analogue is a potent inhibitor of IspG.
- Fluoride is released during the IspG-catalyzed reaction with the inhibitor.
- The results support the involvement of a carbanionic intermediate in IspG's mechanism.

## Abstract

IspG (also known as GcpE) is a key [4Fe‐4S] metalloenzyme that catalyzes the penultimate step of the methylerythritol phosphate (MEP) pathway, a well‐established target for the development of new antimicrobials. This oxygen‐sensitive enzyme mediates the reductive dehydroxylation of 2‐C‐methyl‐d‐erythritol 2,4‐cyclodiphosphate (MEcPP) to (E)‐4‐hydroxy‐3‐methylbut‐2‐en‐1‐yl diphosphate (HMBPP), requiring electron transfer proteins to deliver two electrons needed for catalysis. To probe the mechanism of IspG and access new mechanism‐based inhibitors, we synthesized a substrate analogue, monofluoromethyl‐d‐erythritol cyclodiphosphate, in which the natural methyl group of MEcPP is replaced by a CH2F group. This analogue proved to be a potent inhibitor of IspG. This study also demonstrates that electron capture is a prerequisite for inhibition and that the inhibitor leads to fluoride release in the IspG‐catalyzed reaction. Together, these results provide further support for the involvement of a carbanionic intermediate in the IspG mechanism.

The fluoromethyl analogue of MEcPP was identified as a very potent inhibitor of the oxygen‐sensitive [4Fe‐4S] metalloenzyme IspG. In the course of the IspG‐catalyzed transformation, this novel compound undergoes fluoride elimination, offering additional evidence for the involvement of a carbanionic intermediate in the mechanism of this enzyme.