Canthin-6-one alkaloids and a tirucallanoid from Eurycoma longifolia and their cytotoxic activity against a human HT-1080 fibrosarcoma cell line.

Phytochemical investigation of the stems of Eurycoma longifolia Jack led to the isolation of two new canthin-6-one alkaloids, 4,9-dimethoxycanthin-6-one (1) and 10-hydroxy-11-methoxycanthin-6-one (2), and a new tirucallane-type triterpenoid, 23,24,25-trihydroxytirucall-7-en-3,6-dione (3), along with 37 known compounds. Among these, an oxasqualenoid (4) was isolated as a natural product for the first time. The structures of the isolates were elucidated by spectroscopic and mass spectrometric means. All the isolates were evaluated for their cytotoxic activity against a HT-1080 human fibrosarcoma cell line. Among them, 9,10-dimethoxycanthin-6-one (14, IC50 = 5.0 microM), 10-hydroxy-9-methoxycanthin-6-one (15, IC50 = 7.2 microM), dihydroniloticin (18, IC50 = 8.2 microM), and 14-deacetyleurylene (34, IC50 = 3.2 microM) displayed stronger activity than the positive control 5-FU (IC50 = 9.2 microM).