Synthesis And Insecticidal Acaricidal&Activities Of Novel Thiadiazole Amide Derivatives Of N-Substituted Benzylmatrinic Acids

Matrine,a naturally quinolizidine alkaloid,is isolated from the roots and rhizomes of Sophora flavescens.Especially matrine shows the insecticidal activities on insect pests.Due to its containing the N-C-S toxic group,1,3,4-thiadiazole has received much research attention.In order to further clarify the relationship between their structures and insecticidal/acaricidal activity,herein a series of thiadiazole amide derivatives of N-substituted benzyl matrinic acids were designed and synthesized by introducing the active1,3,4-thiadiazole.Three results were obtained as follows:1.Twenty-seven compounds were prepared,including three intermediates and twenty-four new thiadiazole amide derivatives of N-substituted matrinic acids.Their structures were all characterized by ¹H NMR,m.p.,IR,and optical rotation.2.Their insecticidal activity was evaluated at 1 mg/mL against the pre-third-instar larvae of Mythimna separata?oriental armyworm?.Among all derivatives,compounds 3e,3h,3n,3w,6c and 7c exhibited more promising insecticidal activity with the final mortality rates greater than 50%,when compared to their precursor matrine?27.6%?and the positive control toosendanin?48.3%?.In the course of bioassay,some larvae with the slim and wrinkled bodies died at the larval stage,some larvae molted to malformed pupae or died during the pupation period,and malformed moths also appeared with imperfect wings3.Their acaricidal activity was assessed at 0.5 mg/mL against the female adult of Tetranychus cinnabarinus.Among all derivatives,compounds 7a and 7b exhibited more promising acaricidal activity with 72h mortality rates greater than 50%,when compared to their precursor matrine.Especially the LC₅₀ of 7b(LC₅₀:0.3313 mg/mL)was about 10 times more than matrine(LC₅₀:3.2286 mg/mL).The preliminary structure-activity relationship analysis showed that introduction of the electron-withdrawing group?NO₂?on the phenyl of 1,3,4-thiadiazole was necessary for the insecticidal activity;introduction of the electron-donating group?Me?on the N-benzyl could improve the acaricidal activity;the carboxyl was the active group for N-benzylmatrinic acids bearing the acaricidal activity.