Chemistry And Some Biological Activities Of Benzoquinones Of Embelia Schimperi

Abstract

Embelia schimperi and Embelia keniensis are among the five medicinal Myrsinaceae plants found in Kenya which find a wide range of application in ethnopharmacology as antimicrobials and anthelmintics. The berries and root bark of E. schimperi were extracted with cold ethyl acetate and found to contain mostly benzoquinones. The level of benzoquinones was found to be higher in the berries relative to root bark. Chromatographic separation of the bioassay selected fractions on oxalic acid impregnated silica gel (soaking in 3% oxalic acid in methanol) using various solvent systems for E.. schimperi led to the isolation and identification of embelin (10), methylvilangin (21), myrsinaquinone (56), decylvilangin (76) and decylanhydrovilangin (77), all of which are benzoquinones. Embelia keniensis was only screened (with aid of TLC analysis) for the presence of the benzoquinone pigments and found to contain trace amounts of embelin (19). All these structures were established using physical and spectroscopic (UV, MS, IH, 13C and 2-D NMR) data. Two compounds were not characterized. Biological activity tests such as insect anti-feedant, brine shrimp lethality, larvicidal and anti-microbial were carried out with the pure compounds. Insect anti-feedant tests were determined with Locusta migratoria using a concentration of 100 ug/ml of each sample which was applied on sucrose treated Whatman No.1 filter paper. In the control experiments, the filter papers had sucrose only. Embelin (10) and :u. were found to have relative anti-feedant percentage (RAP) of 96% and 33% respectively. The larvicidal tests were done on mosquito larvae, Aedes aegypti. Compound 21 was the only one tested for this activity and was found to be a growth retardant. Brine shrimp lethality test was done for ~, Z9:.KCP-01 and KCP-06. The LCso values were found to be 120,51,54 and °ug/rnl respectively: Stored products pests test was performed using SitoDhilus zeamais (maize weevil) and Anthoscelides obtectus (bean weevil) for embelin (19) and it was found that the total number of emerged progeny and reproductibility of the two insects were reduced significantly at all concentrations. , Anti-microbial activity test was performed using Candida albicans, Trichophvton metagroohvte, Microsporium gypsum and Escherichia coli for 1~0, n.......,, 5~J~,7~6, 7.-7, KCP-02 and KCP-06 and it was found that all the compounds had less than significant activity against the micro-organisms.