Diastereomerically pure (S)-verbenone-isoxazoline hybrids: Synthesis, molecular structure, Hirshfeld surface analysis, density functional theory, cytotoxic effect, and apoptosis induction

In this paper, a new diastereomerically pure isoxazolines were efficiently prepared from (S)-verbenone, the procedure involves a regioselective and a diastereoselective 1,3-dipolar cycloaddition of nitrile oxides on the monoterpene's enone. The structures of the newly obtained cycloadducts were confirmed by analytical and spectral studies (HRMS, H-1 NMR, and C-13 NMR). The relative stereochemistry of isoxazoline compounds 3a, 3c, and 3d were confirmed by x-ray single crystal analysis. Hirshfeld surface analysis and two-dimensional fingerprint plots were performed to analyze the different intermolecular contacts in crystal packing. Further, density functional theory calculations have been used to analyze the electronic and geometric frontier molecular orbital and molecular electrostatic map analyses of the compounds to predict the reactive site. All compounds were evaluated in vitro for their cytotoxic activity against four human cancer cell lines including fibrosarcoma HT-1080, lung carcinoma A-549 and breast adenocarcinoma (MCF-7 and MDA-MB-231). Compound 3d was the most potent compound especially against HT-1080 and A-549 cancer cells with IC50 values of 21.35 +/- 1.51 and 14.92 +/- 1.74 mu M, respectively. Mechanistically, the compound 3d induced apoptosis by significant caspase activation in HT-1080 and A-549 cancer cell lines utilizing flow cytometric analysis and caspase 3/7 activation assay. The examined compound 3d caused S cell cycle arrest in both HT-1080 and A-549 cells.