Thiolates Chemically Induce Redox Activation of BTZ043 and Related Potent Nitroaromatic Anti-Tuberculosis Agents

Abstract

The development of multidrug resistant (MDR) and extensively drug resistant (XDR) forms of tuberculosis (TB) has stimulated research efforts globally to expand the new drug pipeline. Nitro aromatic compounds, including 1, 3-Benzothiazin-4-ones (BTZs) and related agents, are a promising new class for the treatment of TB. Research has shown that the nitroso intermediates of BTZs that are generated in vivo cause suicide inhibition of decaprenylphosphoryl-β-D-ribose 2′ oxidase (DprE1), which is responsible for cell wall arabinogalactan biosynthesis. We have designed and synthesized novel anti-TB agents inspired from BTZs and other nitroaromatic compounds. Computational studies indicated that the unsubstituted aromatic carbons of BTZ043 and related nitroaromatic compounds are the most electron deficient and might be prone to nucleophilic attack. Our chemical studies on BTZ043 and the additional nitro aromatic compounds synthesized by us and the others confirmed the postulated reactivity. The results indicate that nucleophiles such as thiolates, cyanide and hydride induce non-enzymatic reduction of the nitro groups present in these compounds to the corresponding nitroso intermediates by addition at the unsubstituted electron deficient aromatic carbon present in these compounds. Furthermore we demonstrate here that these compounds are good candidates for the classical von Richter reaction. These chemical studies offer an alternate hypotheses for the mechanism of action of nitro aromatic anti-TB agents in that the cysteine thiol(ate) or a hydride source at the active site of DprE1 may trigger the reduction of the nitro groups in a manner similar to the von Richter reaction to the nitroso intermediates, to initiate the inhibition of DprE1.

Thiosemicarbazonep-Substituted Acetophenone Derivatives Promote the Loss of MitochondrialΔψ, GSH Depletion, and Death in K562 Cells

“…The regeneration of TSC-NO 2 in the futile cycle is consistent with the depletion of GSH by low concentrations of TSC-NO 2 . Another probable mechanism that operates in aerobic conditions is the alkylation of GSH, as described for nitrocompounds [45]. In this regard, this mechanism could operate for the other studied TSC compounds that is consistent with significant GSH depletion only at concentrations ≥ 50  μ M. The present study provided considerable insight into the mechanisms by which these TSC-derivatives exert their effects, and these investigations should be continued in future specific and detailed studies.…”

“…This putative mechanism is inspired by the mechanism proposed by Tiwari et al [45] for the formation of nitroso-intermediates of nitroaromatic compounds with antituberculosis (TB) activity. Nitroaromatic compounds, such as 1,3-benzothiazin-4-ones (BTZs) and similar compounds, generate nitroso-intermediates in vivo that are able to cause suicide inhibition of decaprenylphosphoryl- β -D-ribose 2′ oxidase (DprE1).…”

Design, Syntheses, and Anti-TB Activity of 1,3-Benzothiazinone Azide and Click Chemistry Products Inspired by BTZ043

“…Therefore, cine addition of either thiolate from the active site cysteine of DprE1 or hydride from a cofactor FADH 2 may be responsible for the generation of the nitroso intermediate at the enzyme active site. 10 It should be noted that in the absence of the enzyme, such nitroso intermediates, undergo dimerization or subsequent reduction (s) to hydroxylamines and amines. 10 We envisioned that the substitution of the nitro group of the 1,3-benzothiazinone scaffold by an electron withdrawing azide group (3, Figure 1) could result in a similar mode of activation and/or inhibition because the first nucleophilic step of a cine addition by either the thiolate from the essential cysteine or hydride from FADH 2 would still occur similar to that shown in Figure 2B.…”

M-Dinitroaromatic Moiety as a Fragment of Biologically Active Compounds

“…For example, DNBA analogs that were prepared by replacing a nitro group by trifluoromethyl or amide by sulfonamide possessed coccidiostatic activity [31,36,55]. A study of DNBA anion-radical analogs showed that active compounds had characteristically increased unshared electron density in the 6-position [56 -58].…”