Modulation of the Meisenheimer complex metabolism of nitro-benzothiazinones by targeted C-6 substitution.

Tuberculosis, caused by Mycobacterium tuberculosis, remains a major public health concern, demanding new antibiotics with innovative therapeutic principles due to the emergence of resistant strains. Benzothiazinones (BTZs) have been developed to address this problem. However, an unprecedented in vivo biotransformation of BTZs to hydride-Meisenheimer complexes has recently been discovered. Herein, we present a study of the influence of electron-withdrawing groups on the propensity of HMC formation in whole cells for a series of C-6-substituted BTZs obtained through reductive fluorocarbonylation as a late-stage functionalization key step. Gibbs free energy of reaction and Mulliken charges and Fukui indices on C-5 at quantum mechanics level were found as good indicators of in vitro HMC formation propensity. These results provide a first blueprint for the evaluation of HMC formation in drug development and set the stage for rational pharmacokinetic optimization of BTZs and similar drug candidates.

Whole cell hydride Meisenheimer complex biotransformation guided optimization of antimycobacterial benzothiazinones.

Nitrobenzothiazinones (BTZs) are potent active substances against Mycobacterium tuberculosis with currently two investigational drugs in clinical development for the treatment of tuberculosis. BTZs are the first examples for which a metabolic pathway towards transient hydride Meisenheimer complexes (HMC) has been shown in mammals, including humans. In this study, lead optimization efforts on BTZs are guided by the systematic evaluation of the HMC formation propensity combined with multiparameter assessment. For this purpose, a novel cell-based assay was specifically developed and fully implemented, and a library of 5- and 7-substituted BTZs was prepared to study substituent effects on the HMC formation. The multiparameter optimization revealed 5-methylated BTZs as the most preferred scaffolds, demonstrating a reduced HMC formation propensity combined with potent activity and good microsomal stability in vitro. In vivo experiments showed good systemic exposure upon oral administration and efficacy in a murine M. tuberculosis infection model. This study reports a qualified in vitro HMC assay, which not only enabled the selection of next-generation BTZs with improved pharmacokinetic properties but also allowed forecasting their in vivo metabolism.