ABSTRACT

Three compounds 3β-lup-20 (29)-en-3-ol (lupeol, LS 1), (3S,8S,9S,10R,13R,14S,17R)-17-[(E,2R,5S)-5-ethyl-6-methylhept-3-en-2-yl]-10,13-dimethyl-2, 3, 4, 7, 8, 9, 11, 12, 14, 15, 16, 17-dodecahydro-1H-cyclopenta [a] phenanthren-3-ol (Stigmasterol, LS 2) and 3, 5, 7-trihydroxy-2-(4-hydroxy-3-methoxyphenyl) chromen-4-one (isorhamnetin, LS 3) were isolated from the hexane and dichloromethane soluble fractions of the stembark of Lonchocarpus sericeus Poir Kunth EX DC (Papilionaceae), a medicinal plant commonly used traditionally in the treatment of inflammation and pains, using column, thin layer and preparative thin layer chromatographic techniques. The chemical structure of these isolated compounds were elucidated by spectroscopic methods including GC-MS, ESI-MS, IR, 1H, 13C, 2D NMR experiments and by direct comparison with literature values. Preliminary phytochemical screening revealed that the stembark of L. sericeus is rich in alkaloids, cardiac glycosides, flavonoids, saponins, tannins and terpenes. Quantitative determinations of some bioactive constituents of the plant showed a higher flavonoid content (0.52 ± 0.02 mg/ 100 g) compared to alkaloids (0.36 ± 0.02 mg/100 g) and saponins (0.49 ± 0.03 mg/). Acute toxicity test (LD50) revealed very low level of toxicity (3,100 mg/kg, i. p mice). This implies the decoction of this plant part at this dose regime is not expected to produce any adverse effect. The anti-inflammatory and analgesic studies revealed that the methanol extract, hexane, dichloromethane, aqueous fractions as well as the isolated compounds ( LS 1 and LS 2 ) effectively reduced oedema caused by egg albumin and xylene and exhibited high analgesic properties in inhibiting pain induced by acetic acid and heat. These reductions were dose-dependent and statistically significant (P < 0.05 - 0.001) when compared to distilled water and similar to prototype drugs employed. This study has therefore identified 3β-lup-20(29)-en-3-ol (LS1) and stigmasterol (LS2) as the active anti-inflammatory and analgesic principles in the stembark of L. sericeus. The result further validates the use of L. sericeus in the treatment of inflammation and management of pain in folkloric medicine. This is the first report of the isolation of stigmasterol and 3, 5, 7-trihydroxy-2-(4-hydroxy-3-methoxyphenyl) chromen-4-one (isorhamnetin) from the stembark of this leguminous tree Lonchocarpus sericeus