Identification of new lignans in Norway spruce knotwood extracts

In a hydrophilic extract of Norway spruce knotwood, the dominating lignan, 7-hydroxymatairesinol, was partially removed by precipitation, and the resulting mixture was fractionated by flash chromatography and preparative high-performance liquid chromatography (HPLC). In the HPLC fractions, 7 S and 7R-todolactol A, 7'-hydroxylariciresinol, and two stereoisomers of 9'-hydroxylariciresinol were identified by gas chromatography-mass spectrometry (GC-MS) analyses, and their structures were confirmed by nuclear magnetic resonance spectroscopy. The 9'-hydroxylariciresinols were suggested to have the 7S,8R,8'R,9'R and 7R,8R,8'R,9'R configurations, and (-)-7'-hydroxylariciresinol 7S*,7'R*,8R*,8'S*, which indicates a configuration of this structure that has not been reported previously. 7S- and 7R-isoliovil were identified by comparison with previously published GC-MS data, and 7'-oxolariciresinol was tentatively identified on the basis of its mass spectrum. Of these lignans, only 7'-hydroxylariciresinol has been identified previously in Norway spruce. Several other lignans with similar mass spectra as the todolactols, isoliovils, and 7'-hydroxylariciresinol were detected, indicating that they are different stereoisomers of these lignans and/or of liovils. In addition to these lignans, the mass spectra of several other unidentified minor lignans indicated the presence of several tens of previously unidentified minor lignans in Norway spruce knotwood, accounting altogether for approximately 6% of the dry weight of the ethanol extract. 7S-Todolactol A, which was dominating among the new lignans, was found to be very unstable in aqueous solutions. Identification of more of these unidentified lignans may be possible only by access to pure reference compounds.