Synthesis and Larvicidal Activity of Phrymarolin Derivatives against Culex pipiens pallens

Twenty-eight new phrymarolin derivatives, including twenty-one ethers, six esters and a dehydroxy phrymarolin, were prepared from phrymarolin I and the structures of all the derivatives were confirmed by ¹H NMR and ¹³C NMR spectroscopic and MS data analyses. Larvicidal activities of these phrymarolin analogues were assayed against 4th instar larvae of Culex pipiens pallens. The ester derivatives of phrymarolin showed lower larvicidal activity than phrymarolin I, but some of the ether derivatives and dehydroxy phrymarolin showed much higher activity. Two ether derivatives, 1-18 and 1-19, showed significant larvicidal activity with LC₅₀ values of 1.89 and 7.78 mg/L, respectively.