Anomeric hydroxy group

If the anomeric hydroxy group is replaced by a hydrogen atom, the compound is named as an anhydro alditol (2-Carb-26). 

The compounds usually known as monosaccharide anhydrides or glycose anhydrides (earlier glycosans ), formation of which involves the anomeric hydroxy group, are named by the same procedure. In these cases the order of preference of ring size designators is pyranose > furanose > septanose. However, three- or four-membered rings should normally be cited as anhydro if there is a choice. 

Disaccharides which can be regarded as formed by reaction of the two glycosidic (anomeric) hydroxy groups with one another are named, systematically, as glycosyl glycosides. The parent (cited as the glycoside component) is chosen according to 2-Carb-2.1. Both anomeric descriptors must be included in the name. 

Among all the synthetic methods developed for glycosidic bond formation, the trichloroacetimidate method developed by Richard Schmidt and coworkers [18] is probably the most popular and widely used for the synthesis of complex oligosaccharides. Glycosyl trichloroacetimidates can be readily prepared by a base-catalyzed addition of the anomeric hydroxy group to trichloroacetonitrile. The stereochemistry can be influenced by the addition of different bases the use of K2C03 favors formation... 

Deblocking of the anomeric position, protected as the 2-trimethylsilylethyl ether, has been achieved in high yields in examples drawn from mono-, di-, and trisaccharide chemistry [112]. An example is shown in Eq. (66). In the absence of acetic anhydride, the product with a free anomeric hydroxy group is obtained. 

Motherwell, W B, Tozer, M J, Ross, B C, A convenient method for replacement of the anomeric hydroxy group in carbohydrates by difluoromethyl functionality, J. Chem. Soc., Chem. Commun., 1437-1439, 1989. 

For more than a century glycosylations were essentially based on methods where the anomeric carbon of the sugar residue to be coupled served as the electrophile (the glycosyl donor) and the alcohol (the glycosyl acceptor) as the nucleophile [O Fig. 1, (A), (B)]. Alternatively, base-mediated deprotonation of the anomeric hydroxy group generating at first an anomeric... 

The first step activation step) should consist of an activation of the anomeric center under formation of a stable glycosyl donor—best by a catalyzed attachment of a leaving group to the anomeric hydroxy group. 

The special precautions required for reactions with toxic gases make the use of sulfur tetrafluoride inconvenient. However, the introduction of diethylaminosulfur trifluoride (DAST) removes these handling problems since this reagent is a liquid and is safe below 40 3C 38,39. Anomeric hydroxy groups are replaced stereoselectively by diethylaminosulfur trifluoride in high yield40. 

Glycosyl esters are compounds in which a carboxylic acid is esterified with the anomeric hydroxy group of a carbohydrate. In the carotenoid field crocin (545), the digentiobiosyl ester of the C2o-dicarboxylic acid crocetin (538), is the most prominent representative and constitutes the major carotenoid in saffron and also in Gardenia jasminoides. 

Although monosaccharides with a free anomeric hydroxy group react... 

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