Review Stereochemical Diversity in Lignan Biosynthesis*l

Abstract--Literature survey of enantiomeric composItIOns of several lignans isolated from various plants indicated that these plants produce (or accumulate) different enantiomers of the lignans with various enantiomeric compositions. Some are optically pure while the others are mixtures of both enantiomers. The data as well as recent results of enantioselective lignan synthesis with Forsythia and Arctium enzymes indicated that different stereochemical mechanisms are operating to give rise to the different enantiomers in Forsythia spp., Arctium lappa, Wikstroemia spp., Phyllanthus sp., and Zanthoxylum spp., and that metabolic steps to produce the optically pure lignans are probably different in the plants. Thus there is a great diversity in stereochemical mechanisms for lignan biosynthesis in different plants