Characterization of Three Hemicelluloses From the Wood of Amabilis Fir (Abies Amabilis)

Abstract

An arabino-4-0-~~~ethylglucuro~~oxylan (10:14:76), a 1%-ater-soluble galactoglucon~annan (1:1:3), and an alkali-soluble galactoglucomannan (0.1:1:3) have been isolated in yields of 7 , 4 , and 87, from the wood of amabilis fir (Abies amabilis).'The structure of the polysaccharides was established by methylation and periodate oxidation techniques. The xylan (FD 106) contained side chains of (1 + 2)-linked 4-O-methy1-a-~-gl~~curonic acid and (1 -+ 3)-linked a-L-arabinofuranose residues, both attached directly to a linear framework of (1 + 4)-linked 0-D-xylose residues. The galactoglucomannans (pn 76 and 95) contained (1 -+ 6)-linked 0-D-galactopyranosyl residues attached directly to a backbone of (1 + 4)-linked p-D-mannose and p-D-glucose residues. Partial hydrolysis of the two hexosans yielded 10 and 13 oligosaccharides, respectively, containing ( I -+ 4)-p-D-mannose, (1 + 4)-P-~-glucose, and (1 -+ 6)-a-D-galactopyra~~ose residues. The ~nolecular rotations of a series of mannooligosaccharides corresponded t o a value of -54" for the specific rotation of an infinitely long mannan. I t is concluded that the main hernicelluloses it1 amabilis fir wood are the same as those occurring in the wood of gymnosperms from other genera. The same three hemicelluloses are also present in the bark of this species.Among the gymnosperms, members of the genera Ginkgo, Larix, Picea, Pinus, Thuja, and Tsuga have been extensively studied with regard to their main hemicellulose constituents (1). No member of the genus Abies, however, has so far been similarly investigated although inany fir species are both widespread and valuable. The present investigation is concerned with the isolation and constitution of the three principal hemicelluloses in the wood of amabilis fir (Abies amabilis) (Douglas) Forbes). The polysaccharides occurring in the bark of this tree have previously been examined in detail (2, 3). RESULTS AND DISCUSSIOXWhen amabilis fir wood was partially hydrolyzed, the acid portion of the hydrolyzate consisted of galacturonic acid, 4-0-methylglucuronic acid, a galacturonosyl rhamnose, probably admixed with a galacturonosyl glucose, and a 4-0-methylglucuronosyl xylose. The first aldobiouronic acid has previously been isolated from pine wood (4, 5 ) . The third was fully identified as 2-0-(4-0-methyl-a-D-glucosyluronic acid)-D-XI-lopyranose. I t probably originated from the xylan portion of the mood.For isolation of the hemicelluloses, the wood was partially delignified with chlorous acid and the holocellulose was extracted with aqueous potassium hydroxide, giving tu.0 polysaccharides, which were separated by repeated treatment with barium hydroxide. lPresent address: E. I. du Pont de iVenzours and Coi?zpany, Kinston, N.C. 2Present adduess:

Polysaccharides

“…The work described below is essentially that produced during the last two years. An additional frac tionation has been made into water-and alkali-soluble material (31,32,33) and it is suggested that, although the general chemical features of the two fractions are similar, the essential difference between them is the larger num. Comparison of the methods of extraction of the mannose-containing polymers after prior re moval of the xylans with potassium hydroxide solution has illustrated the value of sodium hydroxide plus boric acid as a solvent for the polysacchar ides, and preferential precipitation of the glucomannans from these solutions with barium hydroxide has resulted in quick and easy procedures for their purification.…”

“…It possesses a backbone of mannosyl-glucosyl radicals randomly ar ranged and joined by 1->4,8 linkages; this main chain may be branched once (33,34) or twice (31,35). It possesses a backbone of mannosyl-glucosyl radicals randomly ar ranged and joined by 1->4,8 linkages; this main chain may be branched once (33,34) or twice (31,35).…”

“…It possesses a backbone of mannosyl-glucosyl radicals randomly ar ranged and joined by 1->4,8 linkages; this main chain may be branched once (33,34) or twice (31,35). The isolation of mannobiose, manno triose, and mannotetrose (29,31,33,34,36) demonstrates that contiguous mannose units occur in the polymer. That the mannose units are joined to the glucose residues has been confirmed by the isolation from partial acid hydrolysates of oligo saccharides composed of both sugars.…”

“…The ratio of man nose to glucose varies with the tissue and the type of plant from which the polysaccharide was extracted but is usually about 3: 1 for preparations from soft wood (17, 29) and 1.5: 2 for hardwood (17,30). Contiguous glucose units occur less freqUently, although cellobiose (31,36,37) has been isolated from some par tial hydrolysates. The isolation of mannobiose, manno triose, and mannotetrose (29,31,33,34,36) demonstrates that contiguous mannose units occur in the polymer.…”