4- O-Methyl-D-glucuronic acid

The NMR spectrum of the dry sample showed broad unresolved peaks that correspond to a typical mixture of 4-O-methyl-D-glucuronic acid, L-arabinose and D-xylose, and proteins (Oliveira et al., 2010) (Figure 5). 

The second important group of hemicelluloses found in softwoods are the arabino-(4-0-methylglucurono)xylans, which may make up from 5 to 10% of the dry weight of the wood. These consist of /3-1,4-linked D-xylopyranose units, partially substituted by L-arabino-furanose (at the 3 position) and by 4-O-methyl D-glucuronic acid (at the 2 position). The frequency of these substituent groups is around 1 to 2 residues per 10 xylose units. 

A. F. Bochkov and Ya. V. Voznyi, Sugar ortho esters. Part 8. Synthesis of 4-O-methyl-D-glucuronic acid derivatives, Carbohydr. Res., 32 (1974) 1-8. 

Among the plant polysaccharides there may be mentioned the hemi-celluloses the most common of these contain 4-O-methyl-D-glucuronic acid as branch units linked to a /3-D-xylan backbone.110 The commercially important gum arabic, a soluble polysaccharide produced by Acacia trees and widely used in foods and pharmaceuticals, also contains glucuronic units.111 D-Glucuronic acid has been found in sulfated complex polysaccharides from brown algae.112... 

A pectic polysaccharide containing D-galacturonic acid and terminal units of 4-O-methyl-D-glucuronic acid, along with L-rhamnose and D-galacto-pyranose, was purified from yellow mustard mucilage.124 Pectins are prevalent... 

Aldaric acids or their derivatives undergo ready epimerization in pyridine. Alkaline treatment of 4-O-methyl-D-glucuronic acid in the presence of air affords 4-O-methyl-D-glucaric and -D-mannaric acids as well as lower O-methylaldaric acids.262 The two diastereo-isomeric 3-deoxy-2-C-(hydroxymethyl)pentaric acids obtained from... 

O-methyl-D-glucuronic acid have also been obtained by treatment of alginates with alkali.263... 

Despite indications (from analytical data) that a monomethyl ether of a uronic acid occurs in the hydrolyzates of several polysaccharides, definite evidence for the presence of 4-O-methyl-D-glucuronic acid did not appear until 1948, when White found it in mesquite-gum hydroly-zate.14 Confirmation of its presence therein has since13 appeared, and it has also been found in the hydrolyzates from gum myrrh,6 aspen wood,14 and Eucalyptus regnans wood.16... 

Conversion of the reducing end-unit in 2-0-(4-0-methyl-D-glucosyl-uronic acid)-D-xylose to a tartronic semialdehyde residue (as in LXXVII) facilitated the ready isolation of 4-O-methyl-D-glucuronic acid by acid hy-... 

Wood xylans are characterized by the presence of residues of 4-O-methyl-D-glucuronic acid linked to position 2 of D-xylose in the main xylan chains (XXVI), and, accordingly, the aldobiouronic acid, 0-(4-0-methyl-a-D-glu-cosyluronic acid)-(l —> 2)-D-xylose (IX), is commonly isolated after the graded hydrolysis of such xylans. Partial acid hydrolysis of Monterey pine wood69 furnishes this compound together with the isomeric aldobiouronic acid, 0-(4-0-methyl-a-n-glucosyluronic acid)-(l—>3)-D-xylose, as a minor product, but the role of the (1 — 3)-linked aldobiouronic acid unit in the... 

As previously mentioned, the methyl donor " for the formation of 4-O-methyl-D-glucuronic acid of hemicellulose B proved to be S-adenosyl-L-methionine, as in the formation of the methyl ester of pectin. ... 

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