Lignan biosynthesis in forsythia species

Both (+)-pinoresinol 6a in Forsythia suspensa and (–)-secoisolariciresinol 14a in F. intermedia are formed via a direct stereochemically-controlled coupling of coniferyl alcohol 2 derived moieties (cf. the typical peroxidase-catalysed reaction in the presence of H2O2), and the dibenzylbutyrolactone lignan, (–)-matairesinol 10a, in F. intermedia is formed from a post-coupling modification of (–)-secoisolariciresinol 14a; this transformation has been demonstrated in vivo, and in vitro with a crude enzyme preparation, and represents the first report of an enzyme specifically involved in lignan biosynthesis.