Structure-activity relationships between nitrile analogues and acaricidal activities against Haemaphysalis longicornis.

Abstract

A recent increase in severe fever with thrombocytopaenia syndrome (SFTS) virus cases in Korea has been observed. This virus attacks humans and animals, and no drug is available for its treatment. This study is investigating potential control measures targeting the causative agent, Haemaphysalis longicornis. Lepidium meyenii oil was ≈8.3-, 4.2- and 4.1-fold more active than diethyltoluamide against H. longicornis larvae, nymphs and adults, respectively. The major components of L. meyenii oil were identified as benzyl nitrile (71.64%), followed by ethyl linoleic acid (13.32%), ethyl palmitate (7.81%) and 3-methoxybenzyl nitrile (2.10%). In testing individual components of the oil were tested against H. longicornis adults, the half-maximal lethal dose (LD50) values for benzaldehyde, benzyl nitrile and benzyl isothiocyanate were found to be 9.21, 9.19 and 18.26 μg cm-3, respectively. The acaricidal component was isolated and identified as benzyl nitrile. To establish the structure-activity relationships between nitrile analogues and acaricidal activities, benzyl nitrile (LD50: 0.56, 6.38 and 9.19 μg cm-3) exhibited the highest acaricidal activities against H. longicornis larvae, nymphs and adults, followed by benzoyl nitrile (3.24, 8.36 and 15.47 μg cm-3), phenyl nitrile (5.45, 9.35 and 17.48 μg cm-3) and diethyltoluamide (7.95, 14.81 and 22.12 μg cm-3). However, the presence of allyl, methyl or vinyl functional groups bound to the nitrile group abolished the acaricidal activity. These results demonstrate that L. meyenii oil, benzyl nitrile, benzoyl nitrile and phenyl nitrile represent suitable options for the secure management of H. longicornis. Nevertheless, additional research is essential to develop formulations that enhance the efficacy and safety of the aforementioned acaricides. © 2024 Society of Chemical Industry.