Uronic acids alkylation

Unlike neutral polysaccharides undermethylated acidic polysaccharides cannot be realkylated directly. The Hakomori procedure leads to esterification of uronic acid residues that on further treatment with base will undergo extensive p-elimination. Therefore the methylated acidic polymer should be carboxyl-reduced with LiAFH4 prior to realkylation. This is illustrated by our work (O Neill et al., 1986a) on the extracellular polysaccharide produced by Alcaligenes (ATCC 31555). After a single methylation an excess of branch points was observed which indicated incomplete methylation of position 2 of (l- 3)-linked glucose residues. To confirm this, the methylated polysaccharide was carboxyl-reduced, ethylated, and the alkylated alditol acetates analyzed by GLC-MS. The... 

Alkyl halide, silver oxide (no solvent) 2.1 C(l)-protected esterified uronic acids substances which tend to undergo base-promoted degradation Free sugars and other easily oxidizable substances 0-Acyl groups may migrate... 

Alkyl halide, sodium hydride in DMF 2.4 General Esterified uronic acids and other substances are likely to be modified under strongly basic conditions C-Alkylation instead of 0-alkylation may occur 127], 0-acyl groups are replaced with 0-alkyl groups... 

Figure 7,17 Alkyl D-glycosiduronates from O-unprotected D-uronic acids using FeCl3 or Bp3.0Et2 as catalysts.

Benvegnu T., Plusquellec D., Roussel M., Preparation, surface tension, micelle formation, and liquid crystal property, of (alkyl-D-mannopyranoside)uronic acid derivatives and their use in cosmetics. Patent FR 2840306, WO 2003104248, 2005. 

Chapter 4 includes references to the regioselective alkylation of sugars via trialkylstannylation (ref. 10) and copper(II) chelates (ref. 9), and the use of dicarbonylcyclopentadienyl-iron derivatives for the synthesis of uronic acids is covered in Chapter 15 (ref. 34). 

The chemical name of this reagent is l,3-bis(hydroxymethyl)-4,5-dihydroxy-imidazolidinone-2 but it is usually called DMDHEU or the glyoxal reactant because it is prepared from glyoxal, urea, and formaldehyde. Other methylolamide agents that have been used for producing wrinkle resistance in cotton include the aforementioned urea formaldehyde, dimethylolurea, dimethylolethyleneurea, and formaldehyde adducts of melamines (triazines), acetylenediurea, propyleneurea, uron, triazones, and alkyl carbamates. Reactions between methylolamides and cellulose occur in the presence of acid (or Lewis acid) catalysts and are very fast at elevated temperatures—sufficiently so that they are adaptable to the requirements of rapid, commercial processing of cotton fabrics. 

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