Bioactive compounds from lichen usnea aciculifera vain and usnic acid conjugates

Abstract

Phytochemical investigation of lichen Usnea aciculifera Vain led to the isolation of nine new dimeric xanthones, usneaxanthones A-I (36–44), along with 36 known compounds (1–35, 45). The chemical structures of the isolated compounds were elucidated by a combination spectroscopic data (1D, 2D NMR, HRESIMS), ECD experiments, and single-crystal X-ray as well as comparison of their NMR data with those in the literature. The biological activities of isolated compounds were evaluated for antibacterial, anti-dengue and cytotoxic activites. The results revealed that depsides may have potential as lead compounds for the development of new antibacterial and anti-dengue agents. Futhermore, dimeric xanthones exhibited highly potent cytotoxicity against HT-29, HCT116, MCF-7 and A549 cancer cell lines with IC50 values ranging from 2.41 to 9.86 μM. Among isolated compounds, usnic acid was obtained as a major compound. Twenty-five usnic acid derivatives (UA01–UA25) were synthesized and evaluated on α-glucosidase activity. UA02, UA06, UA08, UA11–UA14, UA16–UA17 and UA24–UA25 were identified as new semisynthetic compounds. For α-glucosidase activity, UA01, UA03–UA04, UA06, UA11–UA13 and UA17–UA18 exhibited potential activity with IC50 from 14.51–99.04 µM compared with acarbose (IC50 93.6 µM) as a positive control.