Two new canthin-6-one alkaloids, 4,9-dimethoxy-5-hydroxycanthin-6-one (1) and 9-methoxy-(R/S)-5-(1-hydroxyethyl)-canthin-6-one (2), together with fifteen known ones were isolated from the roots of Thailand Eurycoma longifolia Jack. Among the known canthin-6-one alkaloids, compounds 9 and 16 were isolated from the Eurycoma genus for the first time. Meanwhile, the nitric oxide (NO) inhibitory activities of all isolates were examined in lipopolysaccharide (LPS)-stimulated RAW264.7 cells at 50 µM. Moreover, a dose-dependent experiment was conducted for active compounds 1, 2, 4, 6, 7, 10, 12-17 at the concentration of 10, 25, and 50 µM, respectively. Consequently, compounds 1, 4, 6, 7, 12, 14, 15, as well as 17 were found to inhibit NO release from RAW264.7 cells in a dose-dependent manner. Two new canthin-6-one alkaloids, 4,9-dimethoxy-5-hydroxycanthin-6-one (1) and 9-methoxy-(R/S)-5-(1-hydroxyethyl)-canthin-6-one (2), together with fifteen known ones were isolated from the roots of Thailand Eurycoma longifolia Jack. Among them, 1, 4, 6, 7, 12, 14, 15, as well as 17 were found to inhibit NO release from RAW264.7 cells in a dose-dependent manner at the concentration of 10, 25, and 50 µM.
Keywords: Anti-inflammatory; Canthin-6-one alkaloids; NO production; RAW264.7 cell; Thailand Eurycoma longifolia jack.