Insect growth inhibitors from Machilus japonica

The neolignans, licarin A [(2 R,3 S,4 R,5 R)-2-(3,4-dimethoxyphenyl)-3,4-dimethyl-5-piperonyltetrahydrofuran], (−)-machilusin and [(2 S,3 S)-2,3-dihydro-7-methoxy-3-methyl-2-(3,4-dimethoxyphenyl)-5- trans-(1-propenyl)-benzofuran], were identified as bioactive constituents in leaves of Japanese Machilus japonica. All compounds exhibited growth inhibition activity against larvae of the insect Spodoptera litura. The most abundant constituent was [(2 R,3 S,4 R,5 R)-2-(3,4-dimethoxyphenyl)-3,4-dimethyl-5-piperonyltetrahydrofuran] (0.05% dry wt), a new natural product, while [(2 S,3 S)-2,3-dihydro-7-methoxy-3-methyl-2-(3,4-dimethoxyphenyl)-5- trans-(1-propenyl)-benzofuran] had the highest activity against the test insect (0.01% dry wt, EC 50=0.13% w/w). A possible synergistic action of these compounds with other M. japonica components is discussed.