New cerebrosides and ceramide with other constituents from the aerial parts of Raphidiocystis mannii Hook. f. and their cytotoxic activities

Two new cerebrosides, raphimanosides A (1) and B (2), and a new ceramide, raphimanide (3), were isolated from the aerial parts of Raphidiocystis mannii Hook. f., along with ten known compounds (4–13). Their structures were fully established, based on extensive analyses of ¹H, ¹³C, DEPT, 2D NMR, ESIMS, and HRESIMS data and chemical conversion. Subsequently, methanol extract, ethyl acetate, and n-butanol soluble portions and the isolated compounds 1–9, 12, and 13 were assayed for their cytotoxic effects against three human cancer cell lines (MCF-7, HeLa and A549). None of the new compounds demonstrated efficacy against the tested cell lines. In contrast, the methanol extract, ethyl acetate soluble portion, and compounds 6, 7, 9, 12, and 13 showed moderate to low activities against different tested cell lines. Ethyl acetate soluble portion and compounds 13 and 7 were the most potent samples with the IC₅₀ value of 41.25 μg/mL, 36.76 μM, and 13.16 μM against MCF-7, HeLa, and A549 cell lines, respectively. To the best of our knowledge, this is the inaugural investigation into the chemical constituents of the genus Raphidiocystis, offering novel insights into the chemotaxonomy of this hitherto poorly understood genus.