Fischer synthesis, glycosides

Reaction with Low Molecular Weight Alcohols - the Fischer Glycoside Synthesis... 

Figure 1.22 The Fischer glycoside synthesis, illustrated by reaction of methanol and glucose. The ring opening and closing reactions are shown as stereospecific, by analogy with transglycosylations, whereas the displacements at Cl of the pyranosides is nonstereopsecific.

The acid used in the Fischer glycoside synthesis was originally HCl (which made the kinetic data reproducible only with difficulty, as in methanol HCl is slowly consumed to form methyl chloride). Nowadays, ion-exchange resins are used preparatively, whilst the data on 4- and 5-O-methylated glycosides were obtained with camphor sulfonic acid. 

Figure 1.23 Formation of straight-chain dithioacetals with thiols. Reactions are probably preassociated 5 n2 reactions similar to the reactions in the Fischer glycoside synthesis, but the thiacarbenium ion is drawn to emphasise that the stability of the dithioacetal reflects, not only the weaker basicity of sulfur as compared to oxygen, but also its lesser ability to stabilise a carbenium ion centre by conjugation (see Section 1.3).

Emil Fiseher established that the sulfuric acid-catalyzed reaction of D-glucose with methanol provides the corresponding methyl D-glucopyr-anoside 9, a reaction now known as the Fischer glycoside synthesis (Scheme 3). This remarkable transformation does not need any protection on the hydrojyl groups of glucose, an approach that remains... 

After his doctoral graduation, Helferich became Emil Fischer s personal assistant for two years, and, from 1913 onwards, a teaching assistant. Together with Fischer, he published a series of papers on glycoside synthesis during this period. His scientific career was then interrupted by the First World War, in which he served as an officer throughout. 

A number of glycosides were available to Fischer by way of the Koenigs-Knorr reaction and his own glycoside synthesis, which involves treatment of... 

How, M. J., Brimacombe, J. S., and Stacey, M., The Pneumococcal Polysaccharides, 19, 303-357 Hudson, C. S., Apiose and the Glycosides of the Parsley Plant, 4, 57-74 Hudson, C. S., The Fischer Cyanohydrin Synthesis and the Configurations of Higher-carbon Sugars and Alcohols,... 

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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