Insecticidal Sesquiterpene from Alpinia oxyphylla against Drosophila melanogaster

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Abstract
In the course of screening for novel naturally occurring insecticides from Chinese crude drugs, an MeOH extract of Alpinia oxyphylla was found to possess insecticidal activity against larvae of Drosophila melanogaster Meigen. From the extract, an insecticidal compound was isolated by bioassay-guided fractionation and identified as nootkatone (1) by GC, GC-MS, and 1H and 13C NMR spectroscopy. In bioassays for insecticidal activity, 1 showed an LC50 value of 11.5 μmol/mL of diet against larvae of D. melanogaster and an LD50 value of 96 μg/adult against adults. Epinootkatol (1A), however, showed slight insecticidal activity in both assays, indicating that the carbonyl group at the 2-position in 1 was the important function for enhanced activity of 1. Keywords: Alpinia oxyphylla; Drosophila melanogaster Meigen.; sesquiterpene; nootkatone; epinootkatol; insecticidal activity; structure−activity relationship