Synthesis and insecticidal activity of β ‐dihydroagarofuran ether analogues

BACKGROUND 1 β , 2 β , 4 α , 6 α , 8 β , 9 α , 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. RESULTS Twenty‐two ether derivatives were synthesised using 1 β , 2 β , 4 α , 6 α , 8 β , 9 α , 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 LD 50 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. CONCLUSION 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. © 2015 Society of Chemical Industry