Methyl uronate from

Methylated uronic acids are usually separated from methylated aldoses by virtue of the insolubility of their barium salts in chloroform. Recently, 4-0-methyl-D-glucuronic acid has been separated from a mixture of non-acidic reducing sugars by absorption on a weakly basic... 

A related strategy starting from a uronic acid was reported to construct the core stmcture of zaragozic acid [122,123]. The key point was the formation of the C4-C5 bond using aldol condensation. As shown in Scheme 11.40, methyl uronate 168 was first treated with KHMDS at —100°C, and then treated with a premixed solution of cerium chloride and (l )-glyceraldehyde acetonide to give the expected aldol as a mixture of diastereoisomers in a yield of 65 to 70%. 

Two-caibon chain-extension by condensation of a-D-i o-pentodialdo-l,4-fiininose derivative 24 with the anion formed from the acetyKron complex 27 gave a 2 1 mixtufe of products 25. Decompl catk>n with MBS in methanol furnished the separable methyl uronates 26." Two methods for three-carbon elongation, both u g thiaa>le based reagents, are illustrated in Scheme 4. As the M ttig route was complementary, in stereochemical terms, to the enolate route and sdective reduction of ketones 2S and 29 was readily adueved by choice of appropriate reaction conditions, ail four stereoisomers 30 were available."... 

N,]S7-bis(methoxymethyl)uron was first isolated and described in 1936 (41), but was commercialized only in 1960. It is manufactured (42) by the reaction of 4 mol of formaldehyde with 1 mol of urea at 60°C under highly alkaline conditions to form tetramethylolurea [2787-01-1]. After concentration under reduced pressure to remove water, excess methanol is charged and the reaction continued under acidic conditions at ambient temperatures to close the ring and methylate the hydroxymethyl groups. After filtration to remove the precipitated salts, the methanolic solution is concentrated to recover excess methanol. The product (75—85% pure) is then mixed with a methylated melamine—formaldehyde resin to reduce fabric strength losses in the presence of chlorine, and diluted with water to 50—75% soHds. Uron resins do not find significant use today due to the greater amounts of formaldehyde released from fabric treated with these resins. 

The floss silk from Chorisia speciosa furnished a polysaccharide with a main chain of (1 -> 4) linked P-Xylp substituted at 0-2 by 5 % of uronic acid. The xylan structure also was interposed with a-Rhap units in small amounts. The defatted seeds furnished on aqueous extraction a major fraction, ((9-acetyl, 10 % and protein, 45 %) wich was hydrolysed and analysed by p.c. and GLC, showing Rha (20 %), Ara (16 %), Gal (64 %) and also uronic acids (45 %). Partial hydrolysis gave rise to a polysaccharide free of arabinose, with 46 % of uronic acids. Methylation analysis (GLC -MS) indicated a chain of (1 4) - linked Gal/ (42 % of 2,3,6-Me3-Gal). 

Neutral sugar, uronic acid and methylation analysis (mol%) of fractionated pectins from ripe red beets... 

Yoshimura and coworkers113 anticipated the formation of a compound of this constitution from an elimination of methyl (methyl 2,3,5-tri-O-methyl-a-D-glucofuranosid)uronate employing potassium terf-butoxide. However, the n.m.r. data reported are not consistent146,147 with this constitution. 

Scheme 11). For methyl (methyl D-glucopyranosid)uronate (27a,b), a-cleavage is accompanied by a rearrangement70 initiated by hydrogen abstraction from the solvent (Scheme 12). 

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