Tetrahydroxanthone-chromanone heterodimers from lichen Usnea aciculifera and their cytotoxic activity against human cancer cell lines

Abstract

Four new tetrahydroxanthone-chromanone heterodimers, usneaxanthones E-H (1-4) together with eleven known compounds (5-15) were isolated from lichen Usnea aciculifera Vain (Parmeliaceae). Their structures and absolute configurations, particularly the central and axial chiralities, were unambiguously demonstrated by a combination of spectroscopic data (1D, 2D NMR, HRESIMS), electronic circular dichroism (ECD) experiments, and single-crystal X-ray crystallographic analyses. The cytotoxicity of new compounds was evaluated on four human cancer cell lines including HCT116 colorectal cancer, MCF-7 breast cancer, A549 lung cancer, and OVCAR-3 ovarian cancer. Compounds 1-4 exhibited good cytotoxicity against all tested cancer cell lines, except ovarian cancer, with the best IC₅₀ value of 3.37 μM. All compounds showed potent cytotoxicity against HCT116 colon cancer with IC₅₀ value from 3.37 to 4.53 μM.

Keywords: Cytotoxicity; Dimeric xanthones; Tetrahydroxanthone chromanone heterodimers; Usnea aciculifera; Usneaxanthones E–H.