Terpenoids from Cleome droserifolia (Forssk.) Del.

A new diacetyl triterpene lactone, drosericarpone (2), was isolated from the hexane extract of the herb Cleome droserifolia, together with buchariol (1, a sesquiterpene oxide, isolated for the first time from Cleome species) and stigmasterol glucoside (3). The structures of 1-3 were identified by spectroscopic means.


INTRODUCTION
Cleome droserifolia (Forssk.) Del. belongs to Family Cleomaceae [1,2]. Cleome species are generally used in folk medicine as stomachics, rubefacients and in the treatment of scabies, rheumatic fever and inflammation [3][4][5][6]. The dried herb of C. droserifolia, locally known as Samwah, Afein, Reeh-El-Bard [7], is used by herbalists in Egypt as a hypoglycemic agent, and its decoction is widely used by the Bedouins of the southern Sinai for the treatment of diabetes [8]. Several studies were carried out to confirm the hypoglycemic effect of the decoction of this herb [8][9][10].

Results and Discussion:
The hexane fraction of the ethanolic extract of the powdered herb of C. droserifolia afforded three terpenoidal compounds 1-3. The identification of these compounds was accomplished by examination of their spectral data ( 1 H-, 13 C-NMR, COSY, HMQC, HMBC and EIMS) and supported by comparison with published data of related compounds [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30].  [24]. The complete assignment of the 13 C-NMR data of 1 was accomplished using 2D NMR spectra (HMQC and HMBC) and is reported here for the first time (Table 1 and Figure 1). Compound 2 was isolated as an oily residue and had a molecular formula of C 34 H 52 O 7 ( 13 C-NMR data and DEPT experiment). Analysis of the 1 H-and 13 C NMR spectra of 2 with the aid of 2D-NMR spectra ( 1 H-1 H COSY, HMQC and HMBC) revealed features characteristic of a triterpene unit containing a 7-membered lactone ring (IR, 1730 cm -1 ) as compared with related compounds isolated from other Cleome species [20,21]. The 1 H-NMR spectrum of 2 showed seven methyl singlet at δ H 1. 15 , and ten quaternary carbons [including three carbonyl carbons (δ c 177.6, 171.8 and 171.0), two olefinic carbons (δ c 135.0 and 136.1), and a carbon bearing OH group at (δ c 69. 8)]. The spectra also revealed the presence of two acetyl groups (δ H 2.0/ δ c 22.8 and 2.03/ δ c 21.2). HMBC correlations of 2 (Figure1) confirmed the gross structure of 2 to be a diacetyl triterpene lactone. The relative stereochemistry at C-7 was confirmed to be 7β-H [7α-H should appear as singlet or br s near δ H 4.7 and H-6 should appear as d (J=1.5 Hz) near δ H 5.9 as confirmed by ROESY [25], while H-7 appears at δ H 5.15 as d (J=10.5 Hz) and H-6 appears at δ H 5.22 as d (J=10.5 Hz)]. The chemical shifts of C-17 and C-21 were found comparable with those of a related compound with 17β-H (C-17 δ H 2.61 dd / δ c 60.5 and C-21 δ H 2.24/ δ c 31.2) [26], suggested the β-orientation of H-17, compared with the data of related compounds with 17α-H [25][26][27][28][29]. The stereochemistry of the double bond at C-20 (22) was proposed to be a Z-type; since the signal for C-21 was observed at δ c 31.5 (C-21 of the E-type is usually observed near δ c 13-15 [25]). From the above data, the structure of 2 was inferred to be as proposed and it was given the name drosericarpone. This compound is reported here for the first time from family Cleomaceae and from nature.

Acknowledgments
I am grateful to Prof. Dr. Meselhy R. Meselhy (Faculty of Pharmacy, Cairo University, Egypt) for NMR measurements and for valuable discussions. Also, to Prof. Dr. Essam Abdel Sattar (Faculty of Pharmacy, Cairo University, Egypt) and Prof. Dr. Ahmed A. Ahmed (Department of Chemistry, El-Minia University, El-Minia, Egypt) for their valuable comments on the spectral data analysis.

Experimental
General M.p. was measured on a Gallekamp melting point apparatus and was uncorrected. 1D-1 H-(500MHz) and 13 C-(125MHz) NMR spectra were recorded at 25°C using (benzene-d 6 ) as solvent and TMS as internal standard on a JEOL 500 Spectrophotometer. 2D-NMR spectra were obtained on a Bruker Avance DRX 400 Spectrophotometer. EI-MS was obtained on Shimadzu PQ-5000 (70 eV) and Bruker Autoflex (Bruker Daltonics, Germany) mass spectrometers. Atmospheric pressure ionization mass spectra (API-MS) were recorded using a PE SCIEX API III bimolecular mass analyzer. Silica gel 60 (70-230 mesh) and Silica gel RP-8 (both from Merck) were used for column chromatography and silica gel 60 H was employed for VLC technique. Centrifugal accelerated radial TLC was performed on a Chromatotron, model no.7924 (Harrison Research Inc. Palo, Alto, Calif., USA). TLC were conducted on precoated silica gel 60 F 254 plates (0.25 mm thickness, Merck), developed with the solvent system MeOH-CHCl 3 (5:95). The TLC plates were visualized by spraying with p-anisaldehyde reagent followed by heating at 110°C.

Plant material
Plant material was collected from the Suez-Cairo desert road, Egypt, in March 2002 and was kindly identified by Dr. M. Gebali (Plant Taxonomy and Egyptian Flora Department, National Research Center, Giza, Egypt). A voucher specimen has been deposited in the herbarium of the Faculty of Pharmacy, Cairo University.