Unlocking secrets of congolese biodiversity: the chemistry of Croton haumanianus (Euphorbiaceae) J. Léonard

Abstract

Croton haumanianus J. Léonard (Euphorbiaceae) is a tree occurring mainly in Congo, Democratic Republic of Congo, Equatorial Guinea and Southern Cameroon. Croton species have produced two marketed drugs, plaunotol from C. stellatopilosus, used to treat ulcers, and Sangre De Drago (or Dragon’s blood) from C. lechleri, which is used in the treatment of inflammation and dysentery. The stem bark of C. haumanianus has been reported to contain two diterpenoids, crotocorylifuran, a clerodane-type, and crotohaumanoxide, a crotofolane-type, and lupeol, a triterpenoid.[1] In the Democratic Republic of Congo, a decoction of the stem bark is used in the treatment of gonorrhea and rheumatism, and as an arrow poison.[2] This research is part of the ongoing project at the University of Surrey investigating the Chemistry of African Croton species. Thirty-two diterpenoids, two sesquiterpenoids, two triterpenoids, and a steroid, syringaldehyde, octyl-trans-ferulate and phaeophytin-b have been isolated from the CH2Cl2 and MeOH extracts of the leaves and stem bark of C. haumanianus. The structures of these compounds, shown below, were determined using NMR spectroscopy, mass spectrometry, and infrared and circular dichroism spectroscopy. Eighteen previously unreported diterpenoids, twelve ent-kauranes, 4-5, 7, 9-10, 12-13, & 15-19, and three ent-clerodanes, 21-23, were obtained along with three ent-isopimaranes, 26, 29, & 31, and the known compounds, 1-3, 6, 8, 11, 14, 20, 24, 25, 27-28 & 30. Compounds 11, 12, 13, 15 showed selective activity against three of the NCI 60 cancer cell lines, the colon (HCT-116), the melanoma (M14) and the renal (786-0) cancer cell lines at a concentration of 10-5 M.