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.

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.

Figures