Anhydro-sugars

Mechanistic and stereoelectronic aspects of anhydro sugar formation are discussed in Ref. 7). 

Polymerization of anhydro sugars is aimed at the synthesis of models of naturally occurring polysaccharides and the preparation of polysaccharides resembling natural products. We briefly summarize the chemical structures of major natural polysaccharides1. 

From the multitude of stereoisomeric monosaccharides only a few are found in natural polysaccharides. Among them are hexoses2  

1 Throughout this chapter, Haworth formulas are generally used. In some cases, conformational formulas are used to indicate particular conformations 

2 Hexose-monosaccharide containing six carbon atoms Pentose-monosaccharide containing five carbon atoms 

Under certain conditions halodesoxy derivatives prepared from trityl ethers may be converted to anhydro sugars. Methyl a-D-glucopyrano-side 3,6-anhydride (XLVII) was prepared in this manner. The corresponding /3-isomer had been described by Fischer and Zach.  

The tosyl esters react like the halogen compounds. Methyl 4-tosyl-2,3,6-triacetyl- 9-D-glucopyranoside (XLVIII), which may be obtained from methyl 6-trityl-/3-D-glucopyranoside (see page 92), did not give a 4-tosyl derivative even on very careful deacetylation. The sulfonic acid residue was split off simultaneously and a peculiar anhydride was formed. Mtiller suggested a methyl 3,4-anhydro-n-hexoside structure (XLIX) for this substance. 

Micheel and Spruck improved the synthesis of a pentaacetyl-o-galactoseptanose by using 6-trityl-2,3,4,5-tetraacetyl-D-galactose diethyl mercaptal as the starting material. 

According to Bredereck and coworkers,5-trityl-l,2,3-triacetyl-D-ribofuranose (L) does not yield triacetyl-n-ribose on detritylation, but rather 2,3-diacetyl-D-ribofuranose 1,5-anhydride (LI). 

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Deoxy-D-jcylo hexose 6-(dihydrogen phosphate) (21) has also been synthesized (2) the reaction sequence makes use of 3-deoxy l 2,5 6-di-O-isopropylidene D-galactofuranose (16), a compound that can be easily prepared from D-glucose (2, 60). The mono-isopropylidene derivative (17) formed by partial hydrolysis of the di-ketal is converted into the 6-tosylate (18) by reaction with one molar equivalent of p-toluenesulfonyl chloride. From this the epoxide (19) is formed by reaction with sodium methoxide. Treatment of the anhydro sugar with an aqueous solution of disodium hydrogen phosphate (26) leads to the 6-phosphate (20)... 

Structure and Reactivity of Anhydro-sugars. Part I. Branched-chain Sugars. Part I. Action of Di-ethylmagnesium on Methyl 2 3-Anhydro-4 6-0-benzylidene-a-D-mannoside, A. B. Foster, W. G. Overend, M. Stacey, and G. Vaughan,/. Chem. Soc., (1953) 3308-3313. 

Interatomic Oxygen-Oxygen Distances (pm) in 3,6-Anhydro Sugar Derivatives... 

Khan KM, Perveen S, Voelter W (2007) Anhydro Sugars Useful Tools for Chiral Syntheses of Heterocycles. 7 325-346... 

VIII. Tables of Properties of Anhydro Sugars and Their Derivatives. 69... 

The two main classes of anhydro sugars are therefore the ethylene oxide and the hydrofuranol types. Other anhydro ring systems are known but the number of representatives of such systems is not great. 

Most investigations of the mechanism of ring scission have been made by studying the action of alkali on ethylene oxide anhydro sugars. These investigations will now be reviewed. 

Anhydro Sugars as Intermediates in the Interconversion of Configurational Isomers... 

Another example of the formation of a 3,6-anhydro ring by the saponification of a 3-tosyl-D-glucose derivative is furnished by the work of Peat and Wiggins11 who were able to isolate derivatives of no less than three anhydro sugars, one of which was 3,6-anhydro-D-glucose, from the... 

V. Anhydro Sugars op the Hydropuranol Type 1. 3,6-Anhydro Hexoses... 

This procedure provided the most important method for the synthesis of anhydro sugars of the hydrofuranol type. 3,6-Anhydro sugars have resulted from the saponification of hexoses esterified at C6 by the following cationogens Br- 3 36 14- 36 CH3 C H4 S020 37, 3S- 39> 40 HO-SCVO-41 42 02N-0-.43 It is very probable that the phosphate ion is also cationogenic and that saponification of a hexose 6-phosphate... 

Our present knowledge of the second type of hydrofuranol anhydro sugars, the 2,5-anhydro hexoses, is less extensive and definite than is the case with the 3,6-anhydro type. The credit for most of the information we have belongs to Levene and coworkers and results from the comprehensive study of hexosamines made by them. A good summary of this work was provided by Levene in 1921.49... 

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