Eight compounds were isolated from the roots of Garcinia polyantha, and identified. Two of them, the xanthone garciniaxanthone I (1), and the triterpene, named garcinane (2), are reported as new natural products. The structures of the new compounds were elucidated on the basis of 1D and 2D NMR spectroscopic studies. The structure of compound 1 was confirmed by Xray crystallography. Among the remaining six known compounds, three were known xanthones [smeathxanthone A (3), smeathxanthone B (4), and chefouxanthone (5)], one benzophenone [isoxanthochymol (6)], one triterpene [magnificol], and one sterol [b -sitosterol]. The in vitro antimalarial activity of isoxanthochymol (6) against Plasmodium falciparum shows strong chemosuppression of parasitic growth.Keywords Garcinia polyantha, garciniaxanthone I, Xray crystallography, xanthones; antimalarial activity
IntroductionThe genus Garcinia of the Guttiferae family is well known to be a rich source of bioactive prenylated xanthones [1ϳ3], triterpenes [4], and benzophenones [5,6]. In continuation of our search for bioactive substances from African medicinal plants, we investigated the methanol extract of the root bark of Garcinia polyantha, a tree distributed in the lowland tropical rainforest of West, East and Central Africa [7,8]. In the current investigation we focused on minor constituents from G. polyantha, and one new xanthone (1), one new triterpene (2), and six known compounds (3ϳ6, magnificol, and b -sitosterol), were isolated (Fig. 1). We report herein the structure elucidation of the eight natural products and their antimalarial activity.
Materials and Methods
General Experimental ProceduresMelting points were determined on a Büchi SMP-20 melting point apparatus and are uncorrected. UV spectra were measured with a UV-210 PC UV. IR spectra were recorded on a SHIMADZU FTIR-8400S spectrometer in KBr disks. EI-MS (ionization voltage 70 eV) and HR-EI-MS mass spectra were recorded on Finnigan MAT double focusing spectrometer Model 8230. 1 H-and 13 C-NMR spectra were recorded with a Bruker Avance 500 MHz NMR spectrometer in CDCl 3 or CDCl 3 /CD 3 OD. Chemical shifts are recorded relative to TMS (dϭ0) internal standard and coupling constants J are reported in Hz. Optical rotation were recorded with a Perkin-Elmer 241