Isolation and enzymatic formation of lignans of Daphne genkwa and Daphne odora

Four lignans - pinoresinol, lariciresinol, secoisolariciresinol, matairesinol - were isolated from each of Daphne odora and Daphne genkwa (Thymelaeaceae). Matairesinol isolated from both plants was optically pure (> 99% e.e.) and dextrorotatory. Pinoresinol and lariciresinol isolated from the plants were not optically pure, and their enantiomeric compositions ranged from 88% to 95% e.e. in favor of (-)-enantiomers. As for secoisolariciresinol, the one from D. odora was optically pure [(+)-enantiomer, >99% e.e.], and that from D. genkwa was 97% e.e. in favor of the (+)-enantiomer. Lignan-synthesizing enzyme activity was detected from a Thymelaeaceae plant for the first time; cell-free extracts from D. genkwa catalyzed the formation of (-)-lariciresinol (23% e.e.) from racemic (+/-)-pinoresinols. The stereochemistry of the enzymatic reaction is discussed in relation to the stereochemical features of the isolated lignans.