FORMATION OF (-)-ARCTIGENIN IN FORSYTHIA INTERMEDIA

Article abstract of DOI:10.1016/S0031-9422(00)95149-5

Forsythia intermedia cell-free extracts were examined for their ability to catalyse the enantioselective and regiospecific O-methylation of matairesinol.In contrast to the enzymatic steps defined from (+)-pinoresinol to (-)-matairesinol, the conversion of matairesinol into arctigenin was not highly enenatioselective; both (+)- and (-)-antipodes of matairesinol served as substrates for methylation, with the naturally occuring (-)-enantiomer slightly preferred.But the cell-free extracts also catalyses the synthesis of (+)- and (-)-isoarctigenins, with (-)-matairesinol again the preferred substrate.Thus the O-methylation of matairesinol, catalysed by F. intermedia cell-free extracts, is neither highly enantioselective nor regiospecific.No evidence that subsequent methylation of either arctigenin or isoarctigenin occured to afford dimethyl matairesinol was obtained, i.e. the O-methyltransferase(s) only catalysed monomethylation.Taken together, it is proposed that post-coupling methylation does not proceed via regiospecific methylation of matairesinol to give arctigenin directly.Instead, regiospecific glucosylation first occurs to afford matairesinoside; subsequent methylation affords arctiin, which is then converted into arctigenin via action of a β-glucosidase. Key Word Index - Forsythia; Oleaceae; O-methyltransferases; glucosyltransferases; lignans; neolignans; biosynthesis; enantioselectivity; regiospecifity; chiral separation.