Cytotoxic and Insecticidal Activities of Derivatives of Harmine, a Natural Insecticidal Component Isolated from Peganum harmala

In a continuing effort to develop novel beta-carbolines endowed with better insecticidal activity, a simple high-yielding method for the synthesis of harmine compounds starting from L-tryptophan has been developed and a series of 1,3-substituted beta-carboline derivatives have been synthesized and evaluated for their cytotoxicity against insect cultured Sf9 cell line in vitro and insecticidal activities against 4th instar larvae of mosquitos, Culex pipiens quinquefasciatus and mustard aphid, Lipaphis erysimi. The results demonstrated that 1-phenyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (compound 2) and methyl 1-phenyl-beta-carboline-3-carboxylate (compound 13) represented the best potential compounds, with Sf9 cells inhibition rates of 71.55% and 60.21% after 24 h treatment at concentrations of 50-200 mg/L, respectively. Both compounds 2 and 13 also showed strong insecticidal activity towards 4th instar larvae of mosquitos with LC50 values of 20.82 mg/L and 23.98 mg/L, and their LC90 values were 88.29 mg/L and 295.13 mg/L, respectively. Furthermore, the LC50 values of compounds 2 and 13 against mustard aphids were 53.16 mg/L and 68.05 mg/L, and their LC90 values were 240.10 mg/L and 418.63 mg/L after 48 h treatment. The in vitro cytotoxicity of these compounds was consistent with the insecticidal activity in vivo. The results indicated that the 1- and 3-positions of the beta-carboline ring deserve further investigation to develop biorational insecticides based on the natural compound harmine as a lead compound.