STRUCTURE-ACTIVITY STUDIES ON ANALOGUES OF 4-METHYLGUAIACOL, A CATTLE ANAL ODOUR CONSTITUENT REPELLENT TO THE BROWN EAR TICK (Rhipicephalus appendiculatus)

Abstract

AbstractPreviously, 4-methylguaiacol, a major constituent of cattle anal odour, was found to have a high repellence on Rhipicephalus appendiculatus. In the present study, 10 structural analogues of the phenol were tested for repellence against R. appendiculatus in order to assess the effects of (i) absence or presence of the 4-alkyl group of varying length, (ii) inclusion of a double bond in the 4-alkyl chain, (iii) linking the two phenolic oxygen in a methylenedioxy bridge, (iv) replacement of the OCH3 with CH3 and inclusion of another CH3 at position 6, and (v) presence of an additional OCH3 group at position 6. The analogues comprised of 2-methoxyphenol (guaiacol), 4-ethyl-2- methoxyphenol, 4-propyl-2-methoxyphenol, 4-allyl-2-methoxyphenol (eugenol), 3,4-methylenedioxytoluene, 2,4- dimethylphenol, 4-ethyl-2-methylphenol, 2,4,6-trimethylphenol, 4-propyl-2,6-dimethoxy-phenol and 4-allyl-2,6- dimethoxyphenol, which were compared at different doses in a two-choice climbing assay set up. Each analogue showed either increased or reduced repellence compared with 4-methylguaiacol. The structural feature that was associated with the highest repellence was 4-propyl moiety in the guaiacol unit (RD75 = 0.031 for 4-propyl-2- methoxyphenol; that of 4-methylguaiacol = 0.564). Effects of blending selected analogues with high repellence were also compared. However, none of the blends showed incremental increase in repellence compared with that of 4- propyl-2-methoxyphenol. We are currently evaluating the effects of controlled release of the compound at different sites on cattle on the behavior and success of R. appendiculatus to locate their predilection feeding site.