Peracetylated sugars

Permethylation of carbohydrates.1 Permethylation of carbohydrates in a solid-liquid system is not possible because of lack of solubility in benzene or methylene chloride. The difficulty can be circumvented by reaction of peracetylated sugars with methyl bromide in C6H6-aqueous NaOH with tetrabutylammonium hydrogen sulfate as catalyst. 

Supercritical C02 is not considered a satisfactory solvent for unprotected carbohydrates, but some peracetylated sugar were stated to act as emulsifiers in C02-water or C02-organic solvent mixtures.354 Ionic liquids have also been shown to solvate carbohydrates at a level allowing preparative processes,355,356 for example for the acetylation sucrose.91 This list of unusual solvents should... 

Peracetylated sugars were purchased from Sigma or Senn Chemicals. 

Synthesis of (3-Peracetylated Sugars (with Pyridine as Catalyst)... 

Pour solution over ice and water then extract the desired peracetylated sugar into chloroform. 

Conversion of the o(-Peracetylated Sugars into Corresponding P-Anomers... 

Perform steps 1-5 from Subheading 3.2.I.I. with a-peracetylated sugars. 

Dilute solution with chloroform, wash with water, dry with anhydrous sodium sulfate, evaporate, and isolate p-anomer of peracetylated sugar by crystallization (diisopropylether). 

Dissolve the peracetylated sugar derivative (1 eq) in dry CH2C12 under an inert atmosphere at room temperature (see Note 2). 

Reaction of peracetylated sugars with iodine in the presence of hexamethyl-disilazane has been reported to afford the corresponding glycosyl iodide.29 Glycosyl iodides have also been prepared by treatment of glycosyl chlorides or bromides with substoichiometric amounts of iodine and DDQ.30 In this instance, DDQ acts to oxidize iodide remaining after the initial attack on the electrophilic iodine. The benefit of this approach is to limit the amount of free iodide is solution, as recycling of iodine at the expense of DDQ is clearly not cost-effective. 

Deacylation. Peracetylated sugars can be regioselectively deacetylated at the anomeric center. 

Chemical-ionization (c.i.) mass spectra have been recorded for a number of sugars and their derivatives. When ammonia was used as the reactant gas, all compounds studied gave an (M + NH ) ion. n-Glu-cose and methyl a-o-glucopyranoside showed, in addition to this ion, a peak corresponding to (M + NH — H2O) and (M + NH — MeOH), respectively. Peracetylated sugars showed only one peak (M + NH ). 

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