# Crystal structure of dihydroneopterin aldolase from Mycobacterium tuberculosis associated with 8-mercaptoguanine, and development of novel S8-functionalized analogues as inhibitors: Synthesis, enzyme inhibition, in vitro toxicity and antitubercular activity

## TL;DR

This study reveals the structure of a key enzyme in tuberculosis bacteria and develops new compounds that inhibit its activity without harming human cells.

## Contribution

The study presents novel S8-functionalized 8-mercaptoguanine analogues as potent and selective inhibitors of Mycobacterium tuberculosis FolB enzyme.

## Key findings

- Compound 3e inhibited M. tuberculosis with a minimum inhibitory concentration in the micromolar range.
- The compounds showed submicromolar IC50 values against the DHNA enzyme activity of MtFolB.
- Compound 3e exhibited no toxicity in HepG2 and Vero cell lines.

## Abstract

The crystallographic structure of the FolB enzyme from Mycobacterium tuberculosis (MtFolB), complexed with its inhibitor 8-mercaptoguanine (8-MG), was elucidated at a resolution of 1.95 Å. A novel series of S8-functionalized 8-MG derivatives were synthesised and evaluated as in vitro inhibitors of dihydroneopterin aldolase (DHNA, EC 4.1.2.25) activity of MtFolB. These compounds exhibited IC50 values in the submicromolar range. Evaluation of the activity for five compounds indicated their inhibition mode and inhibition constants. Molecular docking analyses were performed to determine the enzyme-inhibitor intermolecular interactions and ligand conformations upon complex formation. The inhibitory activities of all compounds against the M. tuberculosis H37Rv strain were evaluated. Compound 3e exhibited a minimum inhibitory concentration in the micromolar range. Finally, Compound 3e showed no apparent toxicity in both HepG2 and Vero cells. The findings presented herein will advance the quest for novel, specific inhibitors targeting MtFolB, an attractive molecular target for TB drug development.