Glucopyranosyl cation

The treatment of sucrose with anhydrous HF89 results in the formation of a complex mixture of pseudooligo- and poly-saccharides up to dp 14, which were detected by fast-atom-bombardment mass spectrometry (FABMS). Some of the smaller products were isolated and identified by comparison with the known compounds prepared86 88 a-D-Fru/-1,2 2,1 -p-D-Fru/j (1), either free or variously glucosylated, was a major product, and this is in accord with the known stability of the compound. The mechanism of formation of the products in the case of sucrose involves preliminary condensation of two fructose residues. The resultant dianhydride is then glucosylated by glucopyranosyl cation.89 The characterization of this type of compound was an important step because it has permitted an increased understanding of the chemical nature of caramels. 

Capon and Thacker (85) have provided good evidence that the isomerization of methyl a and a-glucopyranosides in acidic methanol proceeds by the ejection of the methoxyl group to give the glucopyranosyl cation. The hydrolysis... 

Noyori and coworkers found that tetrafluorosilane or trimethylsilyl tri-flate catalyzes the condensation of appropriately protected glycopyranosyl fluorides with trimethylsilyl ethers or alcohols. The strong affinity of silicon for fluorine was considered to be the driving force for this reaction. In the case of Sip4, attack of a nucleophile on the glycosyl cation-SiFj ion-pair intermediate was anticipated. Thus, condensation of 2,3,4,6-tetra-O-benzyl-a- and - -D-glucopyranosyl fluorides (47a and 47fi) with methyl... 

Several catalysts and initiator systems have been tested for the polymerization of GlcAnBzl3, including the following Lewis acids boron trifluoride and its etherate, phosphorus pentafluoride, titanium tetrachloride, and antimony pentachloride and pentafluoride. Several cationic initiators have also been used, including (triphenylmethyl) antimony hexachloride, 2,3,4,6-tetra-O-acetyl-D-glucopyranosyl hexa-fluorophosphate, acetyl hexafluorophosphate, pentamethylbenzyl hexa-fluorophosphate (most of which were generated in situ), and triethyl-... 

The favored formation of acetylated l-a-deuterio-l,5-anhydro-D-glucitol 78 in labeling experiments has been put forward to support the occurrence of carbohydrate radicals as intermediates in the photolytic decomposition of glucopyranosyl phenyl sulfone acetates104 as well as the Cp2TiBD4193 and zinc-silver/graphite-197 mediated reduction of glycosyl halides. Cationic intermediates would have favored the opposite stereochemistry 26... 

Dasgupta, F, Garegg, P J, Use of the methylsulfenyl cation as an activator for glycosylation reactions with alkyl (aryl) 1-thioglycopyranosides synthesis of methyl 0-(2-acetamido-2-deoxy-(3-D-glucopyranosyl)-(l—+6)-0-a-D-glucopyranosyl-(l— 2)-a-D-glucopyranoside, a derivative of the core trisaccharide of E. coli K12, Carbohydr. Res., 202, 225-238, 1990. 

Glucosides having 2-OH free (12) and products from them were not observed when using 3,4,6-tri-0-acetyl-2-0-benzoyl-a-D-glucopyranosyl bromide as the glycosylating agent. This behavior was rationalized in terms of increased stabilization, on account of R1 being phenyl rather than methyl in cyclic cation 3, as compared to the open forms 4, 8, and 11. 

The preparation, X-ray crystal structure and ab initio calculation of the charge distribution of lV-(2-acetamido-3,4,6-tri-0-acetyl-2-deoxy-p-D-glucopyranosyl)-pyridinium chloride have been reported. The anomeric iV-(2,3,4,6-tetra-0-acetyl-D-glucopyranosyl)-4-dodecylpyridinium bromides were prepared as novel cationic surfactants. The panel of five substituted-pyridinium salts 15 were synthesized from the peracetylated glycosyl chloride of p-D-lV-acetyl-neuraminic acid and used to probe the mechanisms of enzymatic and non-enzymatic hydrolysis of neuraminides. " Detailed analysis of the solvolysis of Af-(2-deoxy-a- and p-D-glucopyranosyl)-4-bromoisoquinolinium tetra-fluoroborate in aqueous alcoholic solvents indicated Sjv2-like transition states. 

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