Extractives in Betula celtiberica stemwood and isolation and identification of diarylheptanoids in the hydrophilic extract

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.