# MEP Pathway: First-Synthesized IspH-Directed Prodrugs with Potent Antimycobacterial Activity

## TL;DR

Researchers developed new prodrugs targeting the IspH enzyme in the MEP pathway, showing strong antimycobacterial activity against Mycobacterium smegmatis.

## Contribution

The first-synthesized IspH-directed prodrugs using the cycloSal strategy demonstrate potent antimycobacterial activity.

## Key findings

- Chlorine-substituted prodrugs 5c and 6c showed stronger antimycobacterial activity than isoniazid.
- Electron-withdrawing substituents enhance prodrug hydrolysis and intracellular release of active inhibitors.
- The cycloSal strategy is effective for delivering phosphorylated inhibitors targeting the MEP pathway.

## Abstract

We report the first synthesis of IspH-directed prodrugs targeting the terminal enzyme of the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway, (E)-4-hydroxy-3-methylbut-2-enyl diphosphate reductase (IspH or LytB). A series of alkyne and pyridine monophosphate cycloSaligenyl (cycloSal) prodrugs were prepared to enhance membrane permeability by masking the phosphate group. The effects of electron-withdrawing (Cl, CF3) and electron-donating (OCH3, NH2) substituents were examined, together with amino acid-functionalized and mutual prodrug analogs. Among the synthesized compounds, chlorine-substituted derivatives 5c and 6c displayed the strongest antimycobacterial activity against Mycobacterium smegmatis, surpassing isoniazid in agar diffusion assays. These results indicate that electron-withdrawing substituents accelerate prodrug hydrolysis and facilitate intracellular release of the active inhibitor. This work provides the first experimental evidence of an IspH-targeted prodrug approach, highlighting the cycloSal strategy as a valuable tool for delivering phosphorylated inhibitors and developing novel antimycobacterial agents acting through the MEP pathway.