Esters reactions with monosaccharides

REACTIONS OF MONOSACCHARIDES WITH BE TA -KETONIC ESTERS AND RELATED SUBSTANCES... 

REACTIONS OF MONOSACCHARIDES WITH BETA-KETONIC ESTERS 101... 

REACTIONS OF MONOSACCHARIDES WITH BBTA-KETONIC ESTERS 105... 

REACTIONS OF MONOSACCHARIDES WITH BF7U-KETONIC ESTERS 107... 

REACTIONS OF MONOSACCHARIDES WITH AETA-KETONIC ESTERS 129... 

REACTIONS OF MONOSACCHARIDES WITH RETA-KETONIC ESTERS 137... 

Enzymic reactions with D-galactose oxidase or L-fucose isomerase were used for identification of the monosaccharide isolated after degradation of the esters. 

Monosaccharides contain a number of alcoholic hydroxyl groups, and thus can react with acid anhydrides to yield corresponding esters. For example, when glucose is treated with acetic anhydride and pyridine, it forms a pentaacetate. The ester functions in glucopyranose pentaacetate undergo the typical ester reactions. 

GarcIa, GonzAlez, F., Reactions of Monosaccharides with fteto-Ketonic Esters and Related Substances, 11, 97-143... 

This sequence serves to exemplify the formation and aspects of reactivity of toluene-p-sulphonate esters in monosaccharide systems, and further to illustrate the selective protection afforded to hydroxyl groups by the formation of cyclic acetals by reaction with carbonyl compounds. Thus reaction of methyl a-D-glucopyranoside (26) with benzaldehyde in the presence of zinc chloride gives the 4,6-acetal (27) (Expt 5.118), wherein two fused six-membered rings of the frans-decalin type are present. As a cognate preparation the reaction of benzaldehyde with methyl a-D-galactopyranoside results in a similar conversion to a 4,6-acetal, but in this case the product is the conformationally flexible system of the cis-decalin type, the most likely conformation being that shown below. 

In contrast to other monosaccharides, activated sialic acid donors are biosynthesized from A -acetylmannosamine (ManNAc) or directly from sialic acids (Sia), including A-acetylneuraminic acid (NeuAc), via a more complex pathway (21). ManNAc is phosphorylated at the at the 6-hydroxyl group and condensed with phosphoenolpyruvate to give A -acetylneuraminic acid-9-phosphate (NeuAc-9-P). Phosphate ester hydrolysis is followed by direct condensation with CTP to give CMP-NeuAc (Figure 3). Sialic acids can intercept this pathway directly via enzymatic reaction with CTP. 

An original, and versatile route toward ulosonic acids has been recently elaborated by Wu et al. [103,104,105], It based on a simple introduction of a-keto acid moiety via propargylation of suitable monosaccharides derived aldehydes and subsequent oxidation of the terminal alkynes. As it is exemplified by preparation of KDO, coupling of 61 with 3-bromopropyne gave the a fr-adduct 139 (Scheme 30). Its bromination using NBS/AgNC>3 provided the bromoalkyne 140, which on reaction with KMnC>4 afforded the desired a-keto acid ester, easily convertible into the anomeric mixture of KDO derivatives 143. The yield of all intermediates were very high. 

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