Phenolic Compounds of Picea obovata Ledeb. Bark

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Chemical composition of a phenolic complex of the Siberian spruce bark (Picea obovata Ledeb.) and a structure of oligomeric phenolic compounds composing the bark were studied. The samples of the spruce bark were collected in the vicinity of Lake Baikal in September 2015. Extractive substances were recovered from the crushed bark by extraction with ethyl acetate at the boiling point of the solvent for 4 h. The resinous substances were extracted from the ethyl acetate extracts with hexane by infusion for three days. The samples of bark after extraction with ethyl acetate were dried from solvent residues, and then water-soluble substances were isolated by extraction with distilled water at 90°C for 4 h. The yields of the extractive substances extracted with ethyl acetate and water from the spruce bark on absolutely dry matter were 3.4 and 6.9%, respectively. The relative percentage content of phenolic compounds in the ethyl acetate extract of the spruce bark was 42.4%. The ethyl acetate extract of a spruce bark, pretreated with hexane, was fractionated on a silica gel column using a mixture of chloroform–acetone as the eluent with an increase in the fraction of the latter (from 0 to 100%). The content of monomeric and oligomeric, polymeric phenolic compounds in the extract was determined. Based on the data of ¹Н and ¹³C NMR spectroscopy, it was established that the flavonoid dihydroquercetin and stilbene glycosides isorhapontin and astringin were the main monomeric phenolic extractive substances of Siberian spruce bark. It was shown that the structure of oligomeric phenolic compounds of the spruce bark includes structural fragments of stilbene glycosides, mainly monomeric blocks with the structure of isorhapontin and astringin.