Antimalarial Benzophenones and Xanthones from Garcinia species.

摘要

Garicina, a genus in the Clusiaceae, is a source of antiparasitic and antimalarial phenolic secondary metabolites, including benzophenones and xanthones. The methanolic extracts of G. livingstonei, G. mangostana, G. spicata, and G. xanthochymus were tested in vitro for antiplasmodial activity against the P. falciparum clone D6. The crude methanolic G. mangostana extract inhibited the clone by 89%, while the G. xanthochymus extract inhibited it by 24%. Neither of the extracts showed any cytotoxicity toward Vero cells. Hexanes, EtOAc, and n-BuOH partitions of a G. xanthochymus seed extract were also screened against the P. falciparum clone D6, the hexanes partition inhibited the clone by 58%, the EtOAc and n-BuOH partitions showed no inhibitory activity. Additionally, compounds identified from Garcinia species were screened in the plasmodial lactase dehydrogenase (pLDH) activity assay. The compounds tested were: aristophenone A (1), cycloxanthochymol (2), gambogenone ( 3), guttiferone A (4), guttiferone E (5), guttiferone H (6), isoxanthochymol (7), xantochymol (8), xanthone (9), mangiferin (10), alloathyriol (11), alpha-mangostin (12), beta-mangostin (13), 3-isomangostin (14), 8-desoxygartanin ( 15), 4-methoxyxanthone (16), 1,5,6-trihydroxyxanthone (17), and 32-hydroxy-ent-guttiferone M (18). Only compounds 5, 6, 7, 12, 13, and 14 showed antiplasmodial activity. The antiplasmodial activities of compounds 5, 6, and 14 have not been previously reported. This is the first report of 7, 12, and 13 having antiplasmodial activity against the chloroquine-sensitive P. falciparum clone D6 and chloroquine-resistant clone W2.;For the benzophenones 8 and 2 the absence of a terminal methylene on the C-8 side chain (cf. 5 and 7) correlates with antiplasmodial activity. Compound 6 with a terminal methylene on C-30 and a cyclohexane from C-7 to C-8 is antiplasmodial. It was concluded that, for benzophenones neither the C-5 nor the C-14 side groups affect antiplasmodial activity. The substitution pattern of both the A and B rings of the xanthones was shown to be important in determining the extent of antiplasmodial activity. An isoprenyl chain was necessary on C-8 for antiplasmodial activity (cf. 12 and 14 ). The results indicate that the antiplasmodial activity is determined by factors other than the hydroxylation of C-4 and C-5 alone as the current structure activity studies indicate.