Banfoxanthone , a new prenylated xanthone from the stem bark of Garcinia ovalifolia ( Guttiferaceae )

Article history: Received on: 10/03/2015 Revised on: 08/04/2015 Accepted on: 21/04/2015 Available online: 27/07/2015 A detailed chemical investigation of the secondary metabolites from the extract of the stem bark of Garcinia ovalifolia led to the isolation of one new prenylated xanthone named banfoxanthone and five known compounds, namely friedeline, canophyllal, ovalifoloneA, 3-methoxycheffouxanthone, endodesmiadol. Prenylated xanthones isolated from Garcinia ovalifolia and others species of genus Garcinia appear to be useful as chemotaxonomic markers in Garcinia.


INTRODUCTION
The genus Garcinia (Guttiferae) is known to produce a variety of biologically active metabolites such as polyisoprenylated benzophenones (Meli Lannang et al., 2010;Gustafson et al., 1992), xanthones (Louh et al., 2008) as well as triterpenoids (Nguyen et al., 2011;Meli Lannang et al., 2008).Some of them exhibited a wide range of biological activities such as cytotoxic, anti-inflammatory, anti-diabetes, anti-fungal, anti-microbial, anti-oxidant and anti HIV activities (Hiroyuki et al., 1996;Nkengfack et al., 2002;Hay et al., 2004;Merza et al., 2004;Lannang et al., 2005).In the continuation of our search for bioactive substances from Garcinia species, we have investigated the hexane and methanol extracts of the stem bark of Garcinia ovalifolia.G. ovalifolia is a tree up to 10-15 m on high, with yellow sticky latex, generally distributed in fringing forests and river banks in West and central Africa (Gustafson et al., 1992), Asia, New Caledonia and Polynesia (Ampofo and Waterman, 1986).

General experimental procedures
Optical rotations were measured in methanol solution on a JASCO digital polarimeter (model DIP-3600).The specific rotation is given in deg cm2 g_1.IR spectra were recorded in CHCl3 on a JASCO A-302 IR spectrophotometer.The 1H, 13C, and 2D-NMR spectra were recorded on a Bruker AMX-500 spectrometer using aceton-d6 as solvent.Homonuclear 1H-1H connectivity were determined by using the COSY 458 experiment.One-bond 1H-13C connectivity were determined by HMQC.Two and three-bond 1H-13C connectivity are determined by HMBC experiment.Proton and 13 C chemical shifts are reported in δ (ppm).Coupling constants (J) were measured in Hz.The EIMS were recorded on a double-focusing mass spectrometer (Varian MAT 311A).HREIMS were recorded on a JEOL HX 110 mass spectrometer.
Column chromatography was carried out with silica gel 60 (70-230 and 240-300 mesh sizes, E. Merck) Precoated silica gel TLC plates (E.Merck, F254) were used to check the purity of compounds, and ceric sulfate spray reagent was used for the visualization of compounds on TLC plates.

Plant material
The stem bark of G. ovolifolia was collected from the village Banganfokam, in the west region of Cameroon in February 2010, and identified by the botanist Dr. Tchiengue Barthelemy.A voucher specimen was deposited at the National Herbarium in Yaounde, Cameroon under Ref.N° 55523/HNC/CAM/Nkambé.

Extraction and isolation of natural products
The air-dried and powdered stem bark of G. ovolifolia (1.7kg) was separately extracted at room temperature for 72H successively with hexane and methanol.The concentrations of the solutions under reduced pressure yielded 37g of hexane extract and 344g of methanol extract.

Identification of natural products
As a continuation of our previous phytochemical investigation of the stem bark of Garcinia ovalifolia, the present study report the characterization of a new prenylated xanthone namely banfoxanthone (1).

Previous work
Previous phytochemical investigations on G. ovalifolia have resulted in the isolation of a variety of secondary metabolites which mainly included Guttiferone E (Gustafon et al.,

Chemotaxonomic significance
Previous work on this species have permitted to isolate endodesmiadiol, friedeline, canophyllol, canophyllal and the same natural products have been isolated in the species belonging to the Guttiferae family.The same natural product, isoxanthochimol has been isolated also in the species Garciniapolyantha (Louh et al., 2008).Prenylatedxanthones appear to be useful as chemotaxonomic markers in Garcinia.