Nicotinic acetylcholine receptor binding of imidacloprid-related diaza compounds with various ring sizes and their insecticidal activity against Musca domestica

Fifteen 5-substituted 1-(6-chloro-3-pyridylmethyl)-2-nitromethylene-1,3- diazacyclohexanes and three other related compounds having a five- or seven-membered ring were synthesized and their biological activities were measured in vivo and in vitro. The insecticidal (in vivo) activity was evaluated against houseflies Musca domestica L under synergistic conditions with propargyl propyl phenyl phosphonate and piperonyl butoxide. The binding activity of each compound to nicotinic acetylcholine receptor in vitro was measured using [125I] alpha-bungarotoxin. The insecticidal activities of the unsubstituted diazacyclohexane analogues were slightly higher than those of the imidazolidine analogues, but the enlargement of ring size to diazacycloheptane lowered the activity. Substitution of 1,3-diazacyclohexane or imidazolidine rings was not generally favourable for the activity, but the unsubstituted 1,3-diazacyclohexane analogue showed the highest binding activity. Ring substitutions and ring enlargement decreased the activity 100-30,000-fold.