Hydride-induced Meisenheimer complex formation reflects activity of nitro aromatic anti-tuberculosis compounds

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.

Synthetic approaches to potent heterocyclic inhibitors of tuberculosis: A decade review

Tuberculosis (TB) continues to be a significant global health concern with about 1.5 million deaths annually. Despite efforts to develop more efficient vaccines, reliable diagnostics, and chemotherapeutics, tuberculosis has become a concern to world health due to HIV, the rapid growth of bacteria that are resistant to treatment, and the recently introduced COVID-19 pandemic. As is well known, advances in synthetic organic chemistry have historically enabled the production of important life-saving medications that have had a tremendous impact on patients' lives and health all over the world. Small-molecule research as a novel chemical entity for a specific disease target offers in-depth knowledge and potential therapeutic targets. In this viewpoint, we concentrated on the synthesis of a number of heterocycles reported in the previous decade and the screening of their inhibitory action against diverse strains of Mycobacterium tuberculosis. These findings offer specific details on the structure-based activity of several heterocyclic scaffolds backed by their in vitro tests as a promising class of antitubercular medicines, which will be further useful to build effective treatments to prevent this terrible illness.

BTZ-Derived Benzisothiazolinones with In Vitro Activity against Mycobacterium tuberculosis

8-Nitro-1,3-benzothiazin-4-ones (BTZs) are known as potent antitubercular agents. BTZ043 as one of the most advanced compounds has reached clinical trials. The putative oxidation products of BTZ043, namely, the corresponding BTZ sulfoxide and sulfone, were reported in this journal (Tiwari et al. ACS Med. Chem Lett. 2015, 6, 128-133). The molecular structures were later revised to the constitutionally isomeric benzisothiazolone and its 1-oxide, respectively. Here, we report two BTZ043-derived benzisothiazolinones (BITs) with in vitro activity against mycobacteria. The constitutionally isomeric O-acyl benzisothiazol-3-ols, in contrast, show little or no antimycobacterial activity in vitro. The structures of the four compounds were investigated by X-ray crystallography and NMR spectroscopy. Molecular covalent docking of the new compounds to Mycobacerium tuberculosis decaprenylphosphoryl-β-d-ribose 2'-epimerase (DprE1) suggests that the active BITs exert antimycobacterial activity through inhibition of DprE1 like BTZs.

New Insight into Dearomatization and Decarbonylation of Antitubercular 4H-Benzo[e][1,3]thiazinones: Stable 5H- and 7H-Benzo[e][1,3]thiazines

8‐Nitro‐4H‐benzo[e][1,3]thiazinones (BTZs) are potent in vitro antimycobacterial agents. New chemical transformations, viz. dearomatization and decarbonylation, of two BTZs and their influence on the compounds’ antimycobacterial properties are described. Reactions of 8‐nitro‐2‐(piperidin‐1‐yl)‐6‐(trifluoromethyl)‐4H‐benzo[e][1,3]thiazin‐4‐one and the clinical drug candidate BTZ043 with the Grignard reagent CH₃MgBr afford the corresponding dearomatized stable 4,5‐dimethyl‐5H‐ and 4,7‐dimethyl‐7H‐benzo[e][1,3]thiazines. These methine compounds are structurally characterized by X‐ray crystallography for the first time. Reduction of the BTZ carbonyl group, leading to the corresponding markedly non‐planar 4H‐benzo[e][1,3]thiazine systems, is achieved using the reducing agent (CH₃)₂S ⋅ BH₃. Double methylation with dearomatization and decarbonylation renders the two BTZs studied inactive against Mycobacterium tuberculosis and Mycobacterium smegmatis, as proven by in vitro growth inhibition assays.