Synthesis and multiscale computational analysis of 6-nitrobenzoxazole-2-thione: electronic structure, intermolecular interactions, and predicted protease inhibition

Abstract

Nitro-substituted benzoxazole-2-thione derivatives constitute an underexplored class of heteroaromatic systems with promising pharmacological potential. In this study, 6-nitrobenzoxazole-2-thione was successfully synthesized via regioselective nitration of benzoxazole-2-thione and fully characterized by IR, ¹H and ¹³C NMR spectroscopy, high-resolution mass spectrometry, and single-crystal X-ray diffraction, confirming its molecular structure and thione tautomeric form. Density functional theory (DFT) calculations performed at the M06-2X-D3/6-311++G(d,p) level reveal a kinetically stable and moderately hard electronic system, characterized by a HOMO–LUMO gap of 6.625 eV and a pronounced electrophilic character. Electrostatic potential mapping highlights highly negative regions localized on the nitro oxygen atoms and the thione sulfur, identifying key sites for hydrogen-bond acceptance and intermolecular recognition. Hirshfeld surface analysis demonstrates that the crystal packing is predominantly governed by dispersive H⋯H interactions, supplemented by directional heteroatom-centered hydrogen bonds. Ligand-based activity prediction (PASS) indicates strong inhibition potential toward aspartic proteases, including saccharopepsin, chymosin, and acrocylindropepsin (Pa ≈ 0.807), which is further supported by molecular docking and molecular dynamics simulations revealing stable binding modes within the enzyme active site. However, ADMET profiling, while confirming favorable drug-like physicochemical properties, highlights significant metabolic and toxicity risks, particularly associated with CYP inhibition and predicted hepatotoxicity, suggesting the need for structural optimization. Overall, this integrative experimental and multiscale computational study establishes 6-nitrobenzoxazole-2-thione as a promising electrophilic heteroaromatic scaffold and provides a comprehensive structure–property–activity relationship framework for the rational design of benzoxazole-based protease inhibitors.