Indicuen, a new hopane from Parmotrema indicum Hale growing in Vietnam

One new hopane-type triterpene, indicuen (1), along with eight known compounds (2-9) were isolated from the n-hexane extract of the lichen Parmotrema indicum Hale. The chemical structures of isolated compounds were identified by interpretation of their spectroscopic data (1D, 2D NMR and HRESIMS) combined with DFT-NMR chemical shift calculations and subsequent assignment of DP4+ probabilities and by comparison with the literature. Indicuen represents for a rare hopane bearing a 1-carboxyethyl substituent at C-21 in lichens. Compounds 1-3 and 5-8 were evaluated for alpha-glucosidase inhibition and cytotoxicity against K562 and HepG2 cancer cell lines. Compounds 1, 5 and 7 exhibited moderate alpha-glucosidase inhibition with IC50 values of 201.1, 156.3 and 187.4 mu M, respectively. Compound 1 also showed weak cytotoxicity toward K562 cell line while others showed no activity.