In the course of screening for novel naturally occurring insecticides from Chinese crude drugs, MeOH extract of rhizomes of Nuphar japonicum DC. was found to give an insecticidal activity against larvae of Drosophila melanogaster Meigen. Four alkaloids, (−)-7-epi-deoxynupharidine (1), (−)-castoramine (2), (−)-nupharolutine (3), and (−)-nupharmine (4), were isolated by bioassy-guided fractionation from the extract. Insecticidal activity against larvae of D. melanogaster was demonstrated; 2 and 1 showed LC50 values of 1.00 and 4.33 μmol/mL of diet concentration, respectively. Acute toxicity against adults of D. melanogaster was also found; 1 had the most potent activity, with an LD50 value of 0.86 μg/adult. 1, 2, and 3 caused acetylcholinesterase inhibitions, at 0.5 mmol/L, of 99.6, 65.0, and 59.7%, respectively; however, 4 had only slight activity in this study. Therefore, 1 and 2 were identified as insecticidal compounds from rhizomes of N. japonicum DC. Structure−bioactivity relationship study indicated the importance of the position of the hydroxyl group and the piperizine skeleton for enhanced activity. Keywords: Nuphar japonicum DC.; Nymphaeaceae; rhizomes; Drosophila melanogaster Meigen; sesquiterpene alkaloids; (−)-7-epi-deoxynupharidine; (−)-castoramine; (−)-nupharolutine; (−)-nuphamine; insecticidal activity; structure−activity relationship

In the course of screening for novel naturally occurring insecticides from Chinese crude drugs, a dichloromethane extract of Podophyllum hexandrum was found to give an insecticidal activity against larvae of Drosophila melanogaster Meigen. From the extract, an insecticidal compound was isolated by bioassay-guided fractionation. The compound was identified as podophyllotoxin (1) by comparison of its spectroscopic characteristics with literature data. In bioassays for insecticidal activity, 1 showed a LC(50) value of 0.24 micromol/mL diet against larvae of D. melanogaster and a LD(50) value of 22 microg/adult against adults. Acetylpodophyllotoxin (1A), however showed slight insecticidal activity in both assays, indicating that the 4-hydroxyl group was an important function for enhanced activity of 1.

A MeOH extract of tubers of Corydalis bulbosa had insecticidal activity against larvae of Drosophila melanogaster Meigen. Four protoberberine alkaloids, (-)-tetrahydroberberine (1), (-)-tetrahydrocopticine (2), (+)-corydaline (3), (()-tetrahydropalmatine (4) and (()-dehydrocorydaline (5) as its iodide were isolated from the extract. Compounds 5, 1 and 2 exhibited LC 50 values toward larvae of D. melanogaster of 0.23 µmol/mL, 0.91 µmol/mL and 1.70 µmol/mL diet concentration, respectively. Against adults, 1 showed the most potent activity with an LD 50 value of 2.5 µg/adult. 1, 2, 3 and 4 inhibited acetylcholinesterase by 78.7, 71.8, 68.2 and 64.6%, respectively, at 1.0mM. Furthermore, 5 showed the most potent activity with inhibition of 61.3% at 0.40 mM. 5, 1 and 2 were identified as insecticidal compounds from C. bulbosa. Investigation of the structure-activity relationship indicated the importance of the methylenedioxyl group and double bonds in the isoquinolizine moiety for enhanced activity of the protoberberine alkaloids.