Isolation, structural elucidation and cytotoxicity of new xanthones from bioactive extracts of Calophyllum soulattri

Calophyllum is widely distributed in tropical areas in the world, primarily in the Indo-Pacific region. Some species of Calophyllum have been used in folk medicine. Previous studies indicated the existence of a variety of secondary metabolites such as xanthones, coumarins, triterpenoids and flavonoids which possess various bioactivities. Extensive chromatography techniques applied on the bioactive hexane and dichloromethane extracts of stem bark of Calophyllum soulattri afforded two new prenylated xanthones, soulattrin (1) and phylattrin (2) along with four other xanthones, macluraxanthone (3), caloxanthone C (4), brasixanthone B (5) and trapezifolixanthone (6). The structural elucidations of these compounds were achieved on the basis of spectroscopic analysis of 1D and 2D NMR spectral data (¹H, ¹³C, DEPT, COSY, HMQC & HMBC) while molecular masses were determined via MS techniques. Compound 1–6 were evaluated for their cytotoxicity towards nine human cancer cell lines, SNU-1 (stomach), HeLa (cervix), Hep G2 (liver), NCI-H23 (lung), K562 (leukimia), Raji (lymphoma), LS174T (colon), IMR-32 (neuroblastoma) and SK-MEL-28 (skin) cells in vitro using the MTT method. All the xanthones isolated exhibited significant cytotoxic activity with low IC₅₀ values ranging from 0.27 to 9.89 µg/mL.