Lignans of Forsythia intermedia

Leaf and stem material of Forsythia intermedia contains four main lignans and their O-glucosides. These were identified as the dibenzylbutyrolactone derivatives (−)-arctigenin, arctiin [(−)-arctigenin 4′-O-glucoside], matairesinol and (−)-matairesinol 4′-O-glucoside, together with the furofuran lignans (+)-phillygenin, phillyrin [(+)-phillygenin 4-O-glucoside], (+)-epipinoresinol and (+)-epipinoresinol 4′-O-glucoside. The lignan contents varied according to tissue type and season. Full spectral data for the lignans are presented. The 1H NOE difference spectra recorded for phillygenin and epipinoresinol necessitate the reversal of earlier chemical shift assignments for axial and equatorial protons on C-9 of furofuran lignans having one axial and one equatorial aryl group (the epi series).