Synthesis and insecticidal activity of β-dihydroagarofuran ether analogues

1β, 2β, 4α, 6α, 8β, 9α, 12-hepthydroxyl-β-dihydroagarofuran is the main skeleton of β-dihydroagarofuran sesquiterpenoids, which exhibit excellent insecticidal activity. To study further the structure-activity relationship of β-dihydroagarofuran sesquiterpenoids towards finding novel botanical pesticides, two series of new structurally modified ether analogues were designed and synthesised, and their insecticidal activities were evaluated.

Twenty-two ether derivatives were synthesised using 1β, 2β, 4α, 6α, 8β, 9α, 12-hepthydroxyl-β-dihydroagarofuran as starting material. Bioassay results indicated that most of the derivatives, particularly compounds 5.1.2, 5.1.3, 5.1.7, 5.2.3, 5.2.6 and 5.2.7, exhibited significant insecticidal activity against the third-instar larvae of the oriental armyworm Mythimna separata. Most importantly, compound 5.2.7 showed the lowest LD50 value of 29.2 µg g(-1) among these synthesised compounds, which provides some important hints for further design, synthesis and structural modification of β-dihydroagarofuran sesquiterpenoids towards developing novel botanical insecticides.

The structure-activity relationship illustrated that the moiety at the 1-position affected the insecticidal activity significantly, and that specifically the derivatives with two or three carbon atoms at the 1-position showed promising insecticidal activity, with mortality over 60%, while those with o-F-Bn and p-F-Bn at the 6-position showed similar activity.