Abstract
As part of our continuing research on isoquinoline acaricidal drugs, this paper reports the preparation of a series of the 2-aryl-1-cyano-1,2,3,4-tetrahydroisoquinolines with various substituents on the N-phenyl ring, their in vitro acaricidal activities against Psoroptes cuniculi, a mange mite, and discusses their SAR as well. The structures of all compounds, including 12 new ones, were elucidated by analysis of UV, IR, NMR, ESI-MS, HR-MS spectra and X-ray diffraction experiments. All target compounds showed varying degrees of activity at 0.4 mg/mL. Compound 1 showed the strongest activity, with a 50% lethal concentration value (LC50) of 0.2421 μg/mL and 50% lethal time value (LT50) of 7.79 h, comparable to the standard drug ivermectin (LC50 = 0.2474 μg/mL; LT50 = 20.9 h). The SAR showed that the substitution pattern on the N-aromatic ring exerted a significant effect on the activity. The substituents 2'-F, 3'-F, 2'-Cl, 2'-Br and 2'-CF3 remarkably enhanced the activity. Generally, for the isomers with the same substituents at different positions, the order of the activity was ortho > meta > para. It was concluded that the target compounds represent a class of novel promising candidates or lead compounds for the development of new tetrahydroisoquinoline acaricidal agents.
Highlights
Mites are ectoparasites that can cause a chronic skin disease, acariasis, which occurs widely in animals and human
The purpose of our current research is to examine in vitro the acaricidal activity of a series of the iminium moiety-modified derivatives of ADHIQs, i.e., 1-cyano-2-aryl-1,2,3,4-tetrahydroisoquinolines (CATHIQs, Figure 1), against P. cuniculi and disclose their SAR
The chemical synthesis of the target compounds is outlined in Scheme 1
Summary
Mites are ectoparasites that can cause a chronic skin disease, acariasis, which occurs widely in animals and human. Psoroptes cuniculi is an animal mite that mainly infects rabbits, goats, horses and sheep [1]. It causes intense pruritus in animals, with the formation of crusts and scabs, reduction of weight gain, and even death [2,3], this mite species causes serious economic losses for the animal industry. Concerns over the environmental damage [7,8] and the toxicity of many acaricides limit their application and reduces the number of safe effective products available. These problems have prompted us to dedicate great efforts to develop new effective and safe acaricides from active natural products
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