First Discovery of Insecticidal Activity of 9,9′-Epoxylignane and Dihydroguaiaretic Acid against Houseflies and the Structure–Activity Relationship

The insecticidal activity of (-)-(8R,8'R)-3,3'-dimethoxy-9,9'-epoxylignane-4,4'-diol (1) against houseflies was clarified for the first time. The activities of other stereoisomers were weaker than that of the (8R,8'R)-stereoisomer. In the course of research into structure-activity relationships involving 30 newly synthesized (8R,8'R)-derivatives, 5-fold higher activity (ED50 = 0.91 nmol/fly) was observed for (-)-(8R,8'R)-3,3',4-trimethoxy-9,9'-epoxylignan-4'-ol (21) than for the naturally occurring compound (1). The activity of 1 was weaker than that of (-)-(8R,8'R)-dihydroguaiaretic acid ((-)-DGA) (4); however, compound 21 showed almost the same level of activity as 4.