Glycosidation, Fischer method

Synthesis of alkyl glycosides by the Fischer method (Ferrier and Collins 1972 Overend 1972 Ferrier 1988 Green 1966)... 

At this point we will look at the limits of usefulness of the Fischer method. A large excess of alcohol must be used, preferably as solvent, to displace the equilibrium in the desired direction. Equatorial anomeric alkoxyl anomers are not easily isolated. This reaction cannot be used with phenols, and aryl glycosides are not accessible. 

Several methods for the preparation of glycosides have been reported.1 The Fischer method,1-3 which consists in treatment of a free... 

In the Fischer method for the synthesis of glycosides, an alcohol and a sugar are condensed by the use of an acid as the catalyst. As has been shown... 

Obviously, the presence of a high concentration of alcohol facilitates the synthesis and high concentration of water the hydrolysis. In the Fischer method for the synthesis of the glycosides (Chapter IV), the catalyst is an acid, but, as shown by the excellent work of Bourquelot, H4rissey, and Bridel, enzymes also may be employed with some advantages over the use of acids. When acids are used, all the various isomers are formed, and the equilibrium is very complex although certain constituents predominate under the equilibrium conditions. The enzymes are very much more selective in their catalysis. Almond emulsin catalyzes the sjmthesis and hydroly-... 

Several methods have been reported for the synthesis of glycosides, that is, sugars that have noncarbohydrate groups attached to the reducing carbon as an acetal. We have already discussed the Fischer method (Chapter 2) for the synthesis of a-glycosides formed between a carbohydrate and an alkyl alcohol. This method is not successful when aryl groups are involved. 

The Fischer- Helferich method, as a direct anomeric-oxygen replacement reaction (Scheme 1, path A), has been very successfully applied for syntheses of simple alkyl glycosides. However, because of its reversibility, it has not gained general importance in the synthesis of complex oligosaccharides and glycoconjugates (1). 

Preparation of NPGs may be carried out by standard procedures for making alkyl glycosides (Scheme 3) [6]. The most direct method is the Fischer glycosidation (5 —> 1, Scheme 3), in which the aldose is treated with n-pentenyl alcohol [8] and an acid catalyst... 

The application of Konigs and Knorr s method of glycoside synthesis to acetyl-L-rhamnosyl bromide by Fischer, Bergmann and Rabe resulted in the formation of a mixture of one sirupy and two crystalline isomeric methyl rhamnoside acetates. When acetylrhamnosyl bromide was treated in anhydrous methyl alcohol with dry silver carbonate at room temperature, the solid part of the reaction product consisted of crystalline needles and cubes. The needles consisted of methyl 9-L-rhamnoside triacetate with the expected normal behavior toward alkaline deacetylat-ing agents. The cubes, consisting of 7-methyl L-rhamnoside triacetate ... 

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