Design and synthesis of isoxazole-functionalized benzene sulphonamides as novel inhibitors of Mycobacterium tuberculosis β-carbonic anhydrases

Abstract

The escalating prevalence of multidrug-resistant tuberculosis (MDR-TB) underscores the urgent need for new classes of antitubercular agents targeting novel pathways. Carbonic anhydrase, a ubiquitous metalloenzyme, catalyses the reversible hydration of carbon dioxide in the CO₂ + H₂O HCO₃⁻ + H⁺ reaction. Suppressing this enzymatic activity has recently been identified as a new pathway for the treatment of Mycobacterium tuberculosis. To address this, a series of isoxazole–sulphonamides was rationally designed, incorporating an isoxazole pharmacophore as the aromatic tail, amide as a linker, and sulphonamide as the zinc-binding group. These compounds were evaluated against Mycobacterium tuberculosis carbonic anhydrases (MtCA 1 and 3) and two human carbonic anhydrases (hCA I and II) to identify selective inhibitors of the bacterial enzymes. The findings indicated that molecules containing an isoxazole pharmacophore with amide-linked benzene-3-sulphonamide were significantly more selective for MtCA 3 than hCA I and II. Among these compounds, 12c, 12e, and 19b had the highest inhibition against the MtCA 3 with K_i values between 0.08–0.09 μM compared to the standard acetazolamide with a K_i value of 0.10 μM. Some of the best compounds exhibited potent and selective inhibition of MtCA 3 over hCA I and II, with the meta- and para-substituted derivatives demonstrating higher selectivity and stronger inhibition. Specifically, compound 19b proved to be 199 and 38 times more selective for MtCA 3 than hCA I and hCA II respectively, compared to the standard drug acetazolamide, which is a non-selective CA inhibitor. The potential of compound 19b as a promising antitubercular agent with a MIC value of 8 μg mL⁻¹ against mc² 6230 was further strengthened by in silico ligand–target interaction studies. Thus, compound 19b is emphasised as a promising lead in the pursuit of new, selective agents targeting MtCA 3.