Structure-activity studies on analogues of 4-methylguaiacol, a cattle anal odour constituent repellent to the brown ear tick (Rhipicephalus appendiculatus).

Previously, 4-methylguaiacol, a major constituent of cattle anal odour, was found to have a high repellency on Rhipicephalus appendiculatus. In the present study, 10 structural analogues of the phenol were tested for repellency 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 OCH with CH and inclusion of another CH at position 6, and (v) presence of an additional OCH 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 concentrations in a two-choice climbing assay set up. Each analogue showed either increased or reduced repellency compared with 4- methylguaiacol. The structural feature that was associated with the highest repellency was 4-propyl moiety in the guaiacol unit (RD = 0.031 for 4-propyl-2-methoxyphenol; that of 4-methylguaiacol = 0.564). Effects of blending selected analogues with high repellency were also compared. However, none of the blends showed incremental increases in repellency compared with that of 4-propyl-2-methoxyphenol. We are currently evaluating the effects of controlled release of this compound at different sites on cattle on the behavior and success of R. appendiculatus to locate their predilection for feeding sites.