Voulkensin C-E, new 11-oxocassane-type diterpenoids and a steroid glycoside from Caesalpinia volkensii stem bark and their antiplasmodial activities

A bioassay guided isolation of potential antimalarial molecules from the stem bark of Caesalpinia volkensii Harms (Fabaceae) achieved three new 11-oxocassane-type diterpenoids named voulkensin C (1), D (2) and E (3) together with one steroid glycoside named 3-O-[beta-glucopyranosyl(1 -> 2)-O-beta-xylopyranosyl]-stigmasterol (4) and seven other known compounds including stigmasterol (5), beta-sitosterol (6), oleanolic acid (7), 3-beta-acetoxyolean-12-en-28-methyl ester (8), voucap-5-ol (9), caesadekarin C (10), deoxycaesaldekarin C (11). The structures of the new compounds were determined on the basis of extensive spectroscopic data (IR, MS, H-1 and C-13 NMR and 2D NMR) analyses. The polar extracts revealed moderate to good antiplasmodial activities against chloquine-sensitive (D6) and -resistant strains (W2) of Plasmodium falciparum. Whereas the pure isolates exhibited limited to moderate antiplasmodial activities with compound 4 showing the highest antiplasmodial activities (IC50 values of 4.44 +/- 0.88 and 2.74 +/- 1.10 mu M against D6 and W2 strains, respectively). These results suggest a possible contribution of phytochemicals from C volkensii stem bark towards inhibition of plasmodial parasites' growth hence potential antimalarial. (C) 2013 Elsevier Ltd. All rights reserved.