Galacturonic derivative

A recent screening of various chiral carboxylic acids has allowed the selection of galacturonic derivative 12 as a very efficient control in the stereochemical course of some Passerini reactions (Scheme 1.5). Although the de seems to be strongly dependent on the isocyanide employed, this result suggests the possibility of employing carboxylic acids as easily removable chiral auxiliaries in the asymmetric synthesis of biologically important mandelamides [16]. 

Bromophenol blue (3.0...4.6) aliphatic carboxylic acids [225 — 228] malonic and lactic acids [229] palmitic and lactic acids [230] malonic, glycolic, malic, citric, tartaric, ketoglutaric, galacturonic and oxalic acids [196] dicarboxylic acids, succinic acid [231] indoleacetic acid, trichloroacetic acid [232] palmitic acid, palmityl- and stearyllactic acid [223] benzoic, sorbic and salicylic acid [234] metabolites of ascorbic acid [235] chloropropionic acid [236] oligogalacturonic acids [237] amino acids, hydrocarbons, mono-, di- and triglycerides [238] xylobiose, xylose, glucose and derivatives [239] sugar alcohols [91] toxaphene [240]... 

Synthesis of Uronic Acids. Part II. 2 3 4-Trimethyl Derivatives of Mannuronic, Glucuronic, and Galacturonic Acids, F. Smith, M. Stacey, and P. I. Wilson, J. Chem. Soc., (1944) 131-134. 

Deoxy-sugars. Part XXI. Synthesis of Some Derivatives of 2-Deoxy-D-galacturonic Acid, W. G. Overend, F. Shafizadeh, and M. Stacey, J. Chem. Soc., (1951) 1487-1489. 

The galacturonic acids of a plant cell wall mainly belong to smooth chains of homopolygalacturonic acid (PGA) and to hairy regions of rhamnogalacturonan I (RGI). In green plants, other uronic acids can be found in hemicelluloses. Provided they are not methylesterified, all these carboxylic acids deprotonate at the more or less acidic pH of wall water. The electrostatic charges of these polyanions are then compensated by cations ultimately derived from the environment. 

L-arabinose molecules combine together in the furanose form to produce an araban. Since enzymes capable of hydrolysing pectic acid to n-galacturonic acid are known to be present in certain plant juices, and since the comparatively low temperature and slightly acid condition of plant materials would tend to favor the transformation of arabinose into the furanose form, the occurrence of the furanose structure in the polysaccharide derived from arabinose is not altogether unexpected. 

The three acid-derived components of the hexuronic acids, namely, 5, 47, and 48, are essentially end products in the reaction. This is quite surprising, as 48 required only decarboxylation to form 2-furaldehyde. However, the rate of decarboxylation of the furoic acid was <2% of that of D-galacturonic acid under similar conditions. Furthermore, no trace of pentoses was noted in any of the reaction mixtures, which eliminates previous suggestions of their role in the mechanism of 2-furaldehyde for-... 

In this clas of materials is grouped the majority of the seed mucilages, the acidity of which is due to a uronic acid (usually D-galacturonic acid) or to a methyl ether derivative of a uronic acid. This presence of D-galacturonic acid as the acidic component of the polysaccharide differentiates the mucilages from the gums, the acidity of the majority of which is due to the presence of D-glucuronic acid, or to one of its methyl ether derivatives (see above). 

Double-tail derivatives were sometimes prepared by short syntheses thus, dithioacetals 9 were obtained by condensation of a free carbohydrate with the corresponding -alkanethiol [50] whereas the 6,6-di-O-alkyl derivatives 29 were synthesized by the reaction of alkyl magnesium bromide with l,2 3,4-di-0-iso-propylidene-D-galacturonic acid [62]. 

In model experiments,205 it was found that concentration of an aqueous solution of the aldonic acids in the presence of hydrochloric acid gives exclusively the 1,4-lactones, which, on subsequent trimethyl-silylation, give only one peak on the chromatogram. This method was successfully employed for the separation of D-galacturonic, D-glucuronic, and D-mannuronic acids. Of the 1,4-lactones examined, only the trimethylsilyl ether of D-mannono-1,4-lactone was obtained in crystalline form. However, all of the derivatives showed characteristic differences in their infrared spectra in the range of 1500 to 600 cm"1. When this method was applied to the determination of uronic acids in a variety of polysaccharides,205 it was impossible to find any hydrolytic conditions under which the uronic acids were quantitatively released and then reduced, a problem experienced by other workers.20 The method was, however, successful in affording a qualitative, microscale procedure for the identification of hexuronic acids (which otherwise are difficult to detect). 

When particulate enzyme preparations from Lemna minor were incubated with UDP-[U-14C]galacturonic acid (UDP-GalA), radioactive label was incorporated into pectic acid and into material soluble in organic solvents. This radioactive material had the solubility properties, and the chromatographic behavior on paper and DEAE-cellulose, of a lipid derivative of GalA however, confirmation awaits further characterization. Its formation is enhanced by UMP, and by addition of a polar, lipid fraction prepared from Lemna minor.98 Transfer of radioactivity from this material to pectic acid has been obtained.177... 

L-Ascorbic acid has also been synthesized from D-galacturonic acid —a hexose derivative not so readily available as D-glucose. In addition, several methods have been reported for the synthesis of 1 starting with L-xylose (a pentose not readily available) and cyanide, or with L-threose (a tetrose not readily available) and a two-carbon fragment. 

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