Chemistry and biological activities of zanthoxylum chalybeum and erythrina excelsa

Abstract

The plants Zanthoxylum chalybeum (Rutaceae) and Erythrina excelsa (Leguminosae), which are both referred to by the Luo vernacular name "Roko", are extensively used in folk medicine in Nyanza province, Kenya. In this study, chemical investigations on the root-bark and biological activity tests on the crude extracts and on some of the isolated compounds have been carried out. Extraction of the root barks of both plants was done by cold percolation using dichloromethane. The crude extracts of Z. chalybeum exhibited both antimalarial and larvicidal activity with LCso value of 0.8 ug/ml and ICso value of 8.8 ug/rnl respectively. The crude extract of E. excelsa showed weak larvicidal activity with LCso value of 145.8 ug/ml, The structures of the pure compounds isolated were elucidated using NMR, ElMS and UV spectroscopy. The root bark of Z. chalybeum yielded the . benzophenanthridi!le alkaloids dihydrochelerythrine (1) and chelerythrine (2), the 2,6diaryl-3,7-dioxabicyc10[3.3.0]octane; lignans (+)sesamin (3) and (-)asarinin (4), the quinolone alkaloid 4-methoxy-N-methyl-quinolin-2-one (5) and the triterpene lupeol (8). Compound (5) is reported here for the second time, as a natural product, and from the genus Erythrina for the first time. The root bark of E. excelsa yielded the prenylated flavonoid lupinifolin (6), with prenylation on ring-A, the rotenoid, deguelin (7) isolated from the genus Erythrina for the first time and stigmasterol (9).