Knots (i.e., branch bases inside tree stems) in spruce trees contained remarkably higher concentrations of lignans and oligolignans than the adjacent stemwood. The amount of lignans in some knots exceeded 10% (w w−1) and some knots contained hundreds of times more lignans than the heartwood in the same tree. However, there were large variations between different species and even between different knots in the same tree. 7-Hydroxymatairesinol was the predominant lignan in knots of Picea abies, P. glauca, P. koraiensis, P. mariana, and P. omorika, while liovil and secoisolariciresinol dominated in P. sitchensis and P. pungens. The lignans occur in free form in knots and are easily extracted with polar solvents. In addition to the true lignans, especially the knots contained large amounts of lignan-related oligomeric aromatic substances, here called oligolignans, consisting of three or four phenylpropane units.
7-Hydroxymatairesinol, but also other lignans, could be extracted in large scale from spruce knots at pulp and paper mills. Other potentially important lignans could be produced from 7-hydroxymatairesinol by semisynthesis. The ready availability of large amounts of lignans and oligolignans now enables research to assess their bioactivity and provide the basis for applications in medicine and nutrition or as natural antioxidants and antimicrobial agents in a variety of technical products.
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