The new ryanodane diterpenes cinnzeylanone, ryanodol 14-monoacetate, and epi-cinnzeylanol have been isolated from Persea indica (Lauraceae). The structure of cinnzeylanone has been determined by X-ray analysis. These compounds proved to be antifeedants against Spodoptera litura. Cinnzeylanol and ryanodol were the most active antifeedants of this plant, with a range of activity close to that of ryanodine. This is the first report on the antifeedant effects of this class of diterpenes. Their structure-activity relationships and possible mode of action are discussed.
In this work, we have studied the antifeedant and insecticidal effects of several natural ryanoid diterpenes. These compounds can be classified in two groups according to their chemical structures: ryanodol/isoryanodol-type (nonalkaloidal type) and ryanodine-type (alkaloidal type) ryanoids. The nonalkaloidal ryanoids were isolated from Persea indica (Lauraceae) while the alkaloidal ryanoids (ryanodines and spiganthines) were isolated from Spigelia anthelmia (Loganiaceae). The effects of these compounds on the feeding behavior and performance (with and without piperonyl butoxide pretreatment) of Spodoptera littoralis larvae and Leptinotarsa decemlineata adults indicate that some strongly deterred these insects, L. decemlineata being less sensitive than S. littoralis. Their antifeedant effects did not parallel their toxic action. Additionally, more than 60% of the nonalkaloidal ryanoids were antifeedants and/or toxic in contrast to 30% of active alkaloidal ones, supporting the hypothesis of a ryanodol-specific mode of action in insects.
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