Isoxazole–Thiazole Hybrids: Synthesis, Structural Characterisation, Carbonic Anhydrase Inhibition, and Molecular Docking Studies

A new series of isoxazole-fused thiazole–oxazole derivatives (11a–n) was rationally designed and synthesised with the aim of developing potent carbonic anhydrase (CA) I and II inhibitors. The synthesis was achieved in five steps starting from 4-bromoacetophenone, involving key intermediates such as hydroxylamine hydrochloride, hydrazine hydrate, thioisocyanate, and various phenacyl bromide derivatives, using ethanol, triethylamine, tetrahydrofuran (THF), and dimethylformamide (DMF) as solvents. The synthetic route included the formation of a β-ketoester, isoxazole ester, hydrazine adduct, thiourea derivative, and, ultimately, a thiazole ring. The structures of the final compounds were confirmed by ¹H-NMR, ¹³C-NMR, IR spectroscopy, and elemental analysis. All compounds were examined as inhibitors of human carbonic anhydrase (hCA) I and II, and all of them inhibited hCA I and hCA II. Kinetic investigation results revealed that these compounds inhibited hCA I and hCA II in a non-competitive manner. To further explore the molecular basis of their inhibitory activity, in silico studies, including molecular docking and 300 ns molecular dynamics (MD) simulations, were carried out against both CA I and CA II isoforms. These simulations provided detailed insights into the dynamic behaviour, stability, and key binding interactions of the compounds within the enzyme active sites, supporting their potential as promising carbonic anhydrase inhibitors.