2842 [CONTRIBUTION FROM THE
DIVISIOSO F APPLIEDBIOLOGY, KATIOSAL
RESEARCH LABORATORIES]
Constitution of Two Aldobiouronic Acids from Wheat Bran Hemicellulose1'? BY G. X.r l ~ a ~AND r s C. T. BISHOP RECEIVED DECEMBER 21, 1955 The acidic hemicellulose of wheat bran, on acid hydrolysis, yielded neutral sugars and a uronic acid fraction. Chromatographic separations of the latter yielded three components of which aldobiouronic acids I1 and I11 were examined in detail. Reduction of their methyl glycoside methyl esters with lithium aluminum hydride followed by hydrolysis yielded D-gluCOse and D-xylose from I1 and 4 - ~ - m e t h ~ l - ~ - g l u cand o s e D-xYlOSe from 111. Methylation of I1 and 111 followed bv lithium aluminum hydride reduction and hydrolysis, yielded, in both cases, 3,4-di-0-methvl-~-xyloseand 2,3,4-tri-0-meth~l-~-glucose. This evidence together with periodate oxidation on the neutral disaccharides obtained b y reduction of I1 and I11 showed that I1 was 2-04 cu-D-glucopyranosyluronic acid)-D-xylose and 111 was 5-O-(~-O-meth~l-a-D-glucopyr~!losyluro~ic acid )-D-X)-lOSe.
Introduction Previous investigation of the hemicellulose of wheat bran showed that the main component was a highly branched araboxylan containing 970 uronic acid. Since various fractionation procedures did not yield distinct and separate fractions, i t was concluded that the product was reasonably homogeneous. The present paper deals with the constitution of two of the uronic acid components. The uronic acid fraction was removed from a hydrolyzate of the hemicellulose by an anion exchange resin and was shown by paper chromatography t o consist of three components. Of these, fractions I1 and 111, whose acid equivalents showed them to be aldobiouronic acids, were studied in detail. Chromatographic examination of a hydrolyzate of I1 indicated the presence of xylose and glucuronic acid ; similar examination of 111 showed xylose and a monomethyl uronic acid component. It was apparent t h a t the severe conditions required for hydrolysis caused considerable destruction of the products. Accordingly, the aldobiouronic acids were converted to their methyl ester methyl glycosides, reduction of which with lithium aluminum hydride yielded the methyl glycosides of the corresponding disaccharides which were now easily h y d r ~ l y z e d . ~The , ~ disaccharide from fraction I1 yielded D-xylOSe and Dglucose, t h a t from fraction 111 giving D-xylose and 4-0-methyl-D-glucose. The unsubstituted sugars crystallized and were identified by melting points and rotations; the 4-0-methyl-D-glucose yielded a characteristic crystalline phenylosazone.6si The high positive specific rotations of the aldobiouronic acids (+9So for fraction 11, +84.4' for fraction 111) indicated that the glycosidic bonds in both of them were in the a-configuration. I n the periodate oxidation of the disaccharide methyl glycoside obtained by reduction of aldobiouronic acid I1 2.9 moles of periodate was consumed and 1.16 moles of formic acid was produced. These data fitted the requirements for a glucose unit linked glycosidically to a xylopyranoside unit through C(2)or C(4). Similar oxidation of the disaccharide methyl glycoside from aldobiouronic acid (1) 128th 1935. (2) (3) (4)
(5) (6)
(7)
Presented in p a r t before t h e Division of Cellulose Chemistr)., Meeting, American Chemical Society, Minneapolis, Rlinn., Issued as S . R . C . N o . 3973. G . A. Adams, Can. J . C h e i n , 33, 5 0 (19;5). M ilbdel Akher and F. Smith, S a t w e , 166, 1037 (19.50). B. Lythgoe and S. Trippett, J . Chem. S O L . 1983 , (1950). R. Schinle, B e y . , 66, 515 (1932). F. Smith, J . Chem. Soc., 2F1D (1951)
I11 showed that the linkage of the inononiethylated uronic acid must have been to C(?)or C(4, of the xylopyranoside unit. To establish whether the glycosidic linkages were located a t C(3)or C(4) of the xylopyranoside units, aldobiouronic acids I1 and I11 were fully methylated. Reduction with lithium aluminum hydride yielded the corresponding glycosides of the disaccharide methyl ethers. Methanolysis and hydrolysis of the disaccharides yielded in each case 3,3-di-O-meth.l-D-sylose and 2,3,4-tri-O-iiiethylD-glucose which were identified by formation of crystalline derivatives. These results showed that in both I1 and 111, the uronic acid moiety was joined glycosidically to C(?,of the D-xl;lose re4due. The above evidence proved t h a t I1 was L'-C-(aD-glucopyranosyluronic acid) xylose and that (I-0-methyl-cr-D-glUCoI,4-ranOsfraction 111was 2-0yluronic acid)-D-xylose. Xldobiouronic acids containing xylose and Dglucuronic acid have been isolated from a number of naturally occurring polysaccharides. Inr-esti~ gations on hemicelluloses of aspen ~ v o o c l ,Scots pine, 9 beechwood,1° corncobs" and flax" have shown that when the D-glucuronic acid contains ;L methyl ether group on C(4)the glycosidic linkage is always a t C(2) of the D-xylose unit. S o such ortler exists when the D-glucuronic acid is unsubstitutcd, , the xylose in it having been found joined to C ( Yof sapote gum13and wheat bran (the present study), t o C(3) of the D-xylose in wheat pear cell wall,16 S e w Zealand flax'; and sunfloTwr heads" and to C(a,of the D-xylose in corncc)bs.lJ Experimental Paper Chromatography.-Chromatographic separations were carried out by the descending method on IVhattnan S o . 1 paper using the following solvents: (-1) ethyl acetate: I ) , ( B ) L'-butanCJ!lc: mater:acetic acid:formic acid (18:4:3: water ( 2 :I), ( C j ethyl a c e t a t e : ~ ~ . r i d i i i e : n . a t e( r2 :1 : 2 ) , ( D ) benzene:ethanol:~vater(169:47: 15) atid ( E )1-1xit:mol: (8) J. K . h-.J u n e s a n d L. E. n ' i i e , ibi,! , 2T;lO ( 1 O . i " . (0) A . I?. S.Gorrod and 1. I
