Bioactive phenolic substances in industrially important tree species. Part 4: Identification of two new 7-hydroxy divanillyl butyrolactol lignans in some spruce, fir, and pine species

A few lignans, that is, 7-hydroxymatairesinol, secoisolariciresinol, lariciresinol, and nortrachelogenin, predominate in a large proportion of the industrially important softwood species used. Some other lignans, of which some still are unidentified, are also present in lower amounts. Softwood knots, i.e., the branch bases inside tree stems,. commonly contain exceptionally large amounts of free aglycone lignans, which has provided a great opportunity to isolate sufficient amounts of softwood lignans for structural characterisation. Here we present the identification and characterisation of two new 9-epimers of 7-hydroxy divanillyl butyrolactol lignans, (7S,8R,8'R,9'R)-4,4',7-trihydroxy-3,3'-dimethoxylignano-9',9'-lactol and (7S,8R,8'R,9'S)-4,4',7-trihydroxy-3,3'dimethoxylignano-9',9'-lactol, in knotwood of Colorado spruce (Picea pungens), from tentative GC-MS analysis to final determination of the structure by NMR spectroscopy and X-ray analysis. Further analyses have verified the occurrence of these lignans, which were earlier incorrectly addressed by our group as isomers of liovil, in several spruce, pine, and fir species.