Terpenoids from Phaulopsis imbricata (Acanthaceae)

1 Laboratory of Natural Products Chemistry, Chemistry Department, University of Dschang, P. O. Box 67 Dschang, Cameroon. 2 Laboratory of Phytochemistry, Institute of Medical Research and Medicinal Plant Studies, (IMPM), P.O. Box 6163, Yaoundé, Cameroon. 3 Laboratory of Pharmacognosy, Interfaculty Centre for Research on Medicine (CIRM), Department of Pharmacy, University of Liège, B36, B-4000, Liège, Belgium.


INTRODUCTION
The genus Phaulopsis (Acanthaceae) comprises about 22 species encountered in tropical Africa and Asia (Ke et al., 2011). Phaulopsis imbricata (Forssk.) Sweet (syn. Aetheilema anisophyllum R.Brown) is an erect herb of about 1 m high mainly distributed in West Africa (Kayode and Omotoyinbo, 2008;Brummet, 2005). It has been used as medicinal plant for the treatment of pain, arthritis, rheumatism, skin diseases, diarrhoea, dysentery, stomachache, nausea and sores (Burkill, 1985). It is also used as chewing stick for oral and dental healthcare (Kayode and Omotoyinbo, 2008). Another species, P. fascicepala, has been reported to possess antioxidant activity (Adesegun et al., 2009).
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License our knowledge, no phytochemical study has been reported from the genus Phaulopsis. This study approach has been to investigate the chemical constituents of P. imbricata. We now report, herein, the isolation and structural identification of two triterpenoids (lupeol and betulin), one carotenoid [(all-E)-lutein], one sesquiterpenoid (cryptomeridiol), and one sterol glycoside (sitosterol 3-O-β-D-glucopyranoside) from the methanol extract of the whole plant of P. imbricata.

General
Melting points (m.p.) were recorded with a Reichert microscope and uncorrected. 1 H NMR (500 MHz) and 13 C NMR (125 MHz) with APT program were recorded at room temperature in CDCl3, using a Bruker DMX 500 spectrometer. The chemical shifts (δ) are reported in parts per million (ppm) with the solvent signals as reference relative to TMS (δ = 0) as internal standard, while the coupling constants (J values) are given in Hertz (Hz). COSY, NOESY, HSQC and HMBC experiments were recorded with gradient enhancements using sine shape gradient pulses. The Infra red (IR) spectra were recorded with a Shimadzu FTIR-8400S Infrared spectrophotometer and Gas chromatography-Mass spectrometry (GC-MS) data were obtained with an Agilent 6890N Network GC system/5975 Inert XL Mass Selective Detector at 70 eV and 20°C. The GC column (VARIAN, USA) was a CP-Sil 8 CB LB/MS, chromapack capillary column (0.25 mm × 30 m, film thickness 0.25 μm). The initial temperature was 50°C for 1 min, and then heated at 10°C/min to 300°C. For the carrier gas, helium was used with a flow rate of 1.20 ml/min. Kovat's retention index (KI) was determined using a calibration curve of n-alkanes. Column chromatography was run on Merck silica gel 60 (70 to 230 mesh) (MERCK, Germany) and gel permeation on Sephadex LH-20 (SIGMA-ALDRICH, St. Louis, MO, USA) while thin layer chromatography (TLC) was carried out on silica gel GF254 pre-coated plates (MERCK, Germany) with detection accomplished by spraying with 50% H2SO4 followed by heating at 100 o C, or by visualizing with a UV lamp at 254 and 365 nm.

Plant
The whole plant of P. imbricata was collected from Bansoa, West Region, Cameroon, in January, 2010. Authentication was done by Mr Paul Mezili, a retired Botanist of the Cameroon National Herbarium, Yaoundé, where the voucher specimen (No. 19290 / SRF / Cam) is deposited.

RESULTS
Compound 1 was obtained as white pellets from MeOH. It had a melting point (m.p.) of 216°C and showed the following spectral characteristics: : 3300,3080,2920,1640,1470,1420,1390,1045,885  ). On the basis of TLC, m.p. and IR analyses, compound 1 was suggested to be lupeol, a lupane-type triterpenoid previously isolated in our laboratory (Tene et al., 2009). The identity of compound 1 was confirmed by comparison of its mass spectrum with that of lupeol in the NIST GC-MS library (NIST, USA).
Compound 5 was identified to sitosterol 3-O-β-Dglucopyranoside after TLC, m.p. and IR analyses, compared to a referenced sample previously isolated in our laboratory (Tene et al., 2008). This compound is widely distributed in plant kingdom.

Conclusion
The phytochemical study of the whole plant of Phaulopsis imbricata (Acanthaceae) afforded five known compounds including lupeol, betulin, (all-E)-lutein, cryptomeridiol and sitosterol 3-O-β-D-glucopyranoside. To the best of our knowledge, this plant is phytochemically studied here for the first time. In addition, pure compounds are here reported for the first time from the genus Phaulopsis. The antimicrobial activity of the extracts and pure compounds from P. imbricata will be evaluated, with a view of verifying the hypothesis that this plant species is used by traditional healers for specific medicinal ends.