Abstract
In Betula celtiberica (Iberian white birch) stemwood, the content and composition of lipophilic and hydrophilic extractives were determined; these have not been reported previously in this species. The total gravimetric amount of extractives was 2.2% of dry wood, of which lipophilic extractives accounted for 0.39% and hydrophilic extractives 1.84% (determined by gas chromatography–flame ionisation detection [GC–FID]). The lipophilic extract contained mainly triterpenoids and steroids. The hydrophilic extract (acetone–water 95:5 v v−1) contained mainly sugars, compounds not eluting on GC, and a large number of unidentified compounds, which accounted for 0.87% of dry wood and dominated the extract. The compounds were isolated from the extract by silica column chromatography and further purified. GC–electron impact (EI)-MS of the silylated compounds showed characteristic mass fragments that suggested them to be diarylheptanoids (DAHs). This is an interesting compound group, as many of them have shown a large variety of beneficial biological effects. Of over 80 detected DAHs, the exact mass of 17 compounds was determined by electrospray ionisation-quadrupole-time-of-flight (ESI-QTOF)-MS, and of these, the structure of 11 compounds was elucidated by nuclear magnetic resonance (NMR). One was a meta,para-bridged diphenylether and 10 were meta,meta-bridged biphenyls, of which one, 3,8,9,17-tetrahydroxy-[7,0]-metacyclophane, has not been described previously. Because of low concentrations, 21 DAHs were only tentatively identified, and of these, as many as 17 seem to be previously undescribed compounds.
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