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The hemicellulose of cherrywood

University of British Columbia

The extractive free cherrywood on alkaline extraction gave, in 22.4 per cent yield, a hemicellulose composed of 106-ll4, 1-4 linked β-D-xylopyranose residues with side chains of 4-0--methyl-D-glucuronic acid attached to position 2 of every 7th anhydroxylose. The hemicellulose on hydrolysis yielded a neutral sugar, D-xylose, with traces of D-glucose and rhamnose. D-Xylose was characterized as the crystalline sugar, D-glucose was characterized as its p-nitroanilide, and rhamnose was characterized by electrophoresis and chromatography. An aldobiouronic acid was isolated from the acidic fragments and shown to be 2-0-(4-0-methyl-⍺-D-glucopyranosyluronic acid)-D-xylose by preparation of the crystalline acetate, methyl 2-0-[methyl (2,3-di-0-acetyl-4-0-methyl-⍺-D-glucopyranosyl) uronate ]-3,4-di-0-acetyl-D-xylopyranoside. The hemicellulose was methylated and the product fractionated to give three main fractions which were essentially homogeneous. Hydrolysis of one of the fractions yielded 2,3,4-tri-0-methyl-D-xylose (l mole) characterized by chromatography 2,3-di-0-methyl-D-xylose characterized as the crystalline sugar and anilide, and 2,3-di-0-methyl-D-lyxose characterized as the crystalline sugar and anilide (88 moles); and 2-0 and 3-0-methyl-D-xylose (l mole) characterized by electrophoresis. Traces of two disaccharides and an unknown monosaccharide were also found. A partially methylated aldobiouronic acid, 3-0-methyl-2-0- (2,3,4-tri-0-methyl-⍺-D-glucopyranosyluronic acid)-D-xylopyranose (l6 moles), was isolated and characterized as follows. The methyl ester methyl glycoside was prepared and then reduced to the disaccharlde. The disaccharide was hydrolysed to give 3-0-methyl-D-xylose and 2,3,-tri-0-methyl-D-glucose characterized as their crystalline anilides. Cherrywood hemicellulose resembles other glucuronoxylans isolated from hardwoods such as sugar maple and white birch but there is a higher uronic acid to xylose ratio than is usual for hardwood xylans. It resembles the xylan from white elm more closely in this respect. Recently apple-wood hemicellulose was isolated and shown to be similar to cherrywood hemicellulose.

Text

2012-02-10

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http://hdl.handle.net/2429/40637

Chemistry

University of British Columbia

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