Anti-Tick Properties of Selected East African Plants against the Brown Ear Tick Rhipicephalus Appendiculatus Neuman and Identification of some of their Secondary Compounds

Abstract

Hexane, ethyl acetate and methanol extracts of Commiphora swynertonii Burtt., Turraea cormicopia (L), T abyssinica, T. floribunda and Melia volkensii Gurke were tested for anti-tick activity against the larvae and adult Rhipicephalus appendiculatus Neuman using the packet method bioassay. The hydrodistilled oil of the leaves of C. swynertonii was tested for acaricidal and repellency activities against ! adult R. appendiculatus using the packet and climbing bioassay method, respectively. Isolation and structural elucidation of pure components from stem bark of C. swynertonii, root bark of T. jloribunda was attempted. Chemical composition of the hydrodistilled oil was carried out using GC and high resolution mass spectrometry. Residual effects of the extracts of T. cormicopia, T abyssinica, T. floribunda and M volkensii were investigated. Hexane and ethyl acetate extracts of C. swynertonii exhibited a mean mortality of 71 % and 54% respectively on two weeks old larvae of R. appendiculatus. These extracts were inactive against adults. The acaricidal activity of the hexane extract was comparable to the commercial acaricide, triatix at the concentration of 0.01 % v/v. The hydrodistilled oil of the leaves of C. swynertonii showed acaricidal and repellency activities against the larvae and adult R. appendiculatus. The oil induced a mean mortality of 84% at the concentration of 1 % v/v. The phytosterol constituents of C. swynertonni, 3p,4a,5-cholest-7-en-3-ol, B-sitosterol, cholest-7-en-3B-ol and ysitosterol exhibited low acaricidal activity against the larvae of R. appendiculatus. Methanol and dichloromethane extracts of the root bark of T cormicopia and T. jloribunda delayed the number of adult female ticks attaching themselves to the ears of the rabbits. They also significantly delayed engorgement time and reduced hatchability of the eggs. Seven pure compounds, six phytosterols and a diol were isolated from the stem bark of C. s-wynertonii. Three limonoids belonging to the class havanensin were isolated from the methanol extract of T. floribunda by preparative High Performance Liquid Chromatography. The limonoids were characterized using 1 H NMR, 13c NMR, 1-D and 2-D COSY, Heteronuclear Multiple Bond Correlation (HMBC) and Mass Spectrometry. These compounds were 28-nor-4a- arbomethoxy-l a, 11 ~-di acetoxy-3, 7-dihydroxy-12a-(2-hydroxy-3-methylbutanoloxy)-l 4, l 5epoxyhavanensin (3 9), 28-nor-3, 7-dihydroxy-4a-carbomethoxy-la, 11 B-diacetoxy l 2a-( 1-methy I propanoloxy)-.6. I 4, 15 havanensin ( 40) and 28-nor-4a-carbomethoxy-1a,11 B-diacetoxy l 2a-(2-methylbutanoloxy)-l 4, 15 epoxyhavanensin ( 41 ). High resolution mass spectrometry of the oil obtained by hydrodistillation of the leaves of C. swynerlonii revealed the presence of fourteen sesquiterpenoids. The major compounds were 9-(furanyl)-2,6-dimethyl-2,6-nonanone, 9-(furanyl-2)-2,6- dimethyl-2,6-nonadien-4-one and 9-(3-furanyl)-2,6-dimethyl)-2,5-nonadien-4-one.