Biosynthesis of Lignans. Part I. Biosynthesis of Arctiin (3) and Phillyrin (5)

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Abstract
Lignans constitute a class of naturally occuring phenolic compounds, widely distributed in higher plants. They are formally composed of two phenylpropanoid units, stercospecifically joined at the /f-carbon atoms of their side chains. Their biosynthesis has as yet not been investigated. To sec, if these plant phenolics originate from simple phenylpropancs, various radioactively labelled, putative precursors were fed to Forsythia shoots. Chemically synthezised arylpropane derivatives, such as Ή/1 'C-glucoferulic acid, -glucoferulic aldehyde, and -coniferin were incorporated into the lignans arctiin (3) and phillyrin (5) while 3H-3,4-dimcthoxycinnamic acid was not incorporated. From these results i t may be concluded that the hydroxylated compounds are direct precursors of these dimeric phenylpropanes and are incorporated through a dimerisation step without degradation of the Q - Q skeleton.