Glycosyl sulfides

Chen, M.-Y., Patkar, L. N., Chen, H.-T., Lin, C.-C. An efficient and selective method for preparing glycosyl sulfoxides by oxidizing glycosyl sulfides with OXONE ort-BuOOH on SI02. Carbohydr. Res. 2003, 338, 1327-1332. 

Glycosyl bromides. Glycosyl sulfides are converted to the bromides by IBr. When DABCO and MeOH are also added, methyl glycosides are obtained. 

Glycosylation. The one-electron oxidant promotes activation of glycosyl sulfides toward coupling with alcohols (including sugars). 

Chen [100] reported the selective oxidation of glycosyl sulfides 183 to sulfoxides 184 by use of magnesium monoperoxyphthalate under the action of microwave irradiation (Scheme 5.52). Sulfoxides 184 were obtained as a mixture of R and S isomers and microwave irradiation reduced the reaction time from 10 to 0.7 h. Interestingly, the R and S isomer ratios are not similar to those reported previously by the same authors [101] and they concluded that these modifications of the selectivity may have been associated with a microwave effect or the oxidant used. 

In a newer application of the Mitsunobu reaction in carbohydrate chemistry, Falconer et al. prepared glycosyl disulfides from a variety of glycosyl sulfides. This particular reaction employs only DEAD as an activating agent. TPP or an equivalent thereof was not needed in this reaction. 

Bu3SnH, AIBN, PhH, 3 h. A, >72% yield. The thiol is released as a stannyl sulfide that was used directly in a glycosylation. " ... 

The transformation of 1-hydroxy sugars to the corresponding glycosyl fluorides can be achieved by a mixture of Selectfluor 3 (Figure 2.2) and methyl sulfide presumably through a fluorosulfonium ion 9, which then reacts with the anomeric... 

Scheme 3.15 Metal oxide and metal sulfide-promoted glycosylations.

Stilbenes, photocyclization of, 30, 1 StiUe reaction, 50, 1 Stobbe condensation, 6, 1 Substitution reactions using organocopper reagents, 22, 2 41, 2 Sugars, synthesis by glycosylation with sulfoxides and sulfinates, 64, 2 Sulfide reduction of nitroarenes, 20, 4 Sulfonation of aromatic hydrocarbons and aryl halides, 3, 4 Swem oxidation, 39, 3 53, 1... 

The bicyclic sugars 121 and 128-130 should all be capable of some sort of chemical activation to produce glycosyl donors. To date, we have investigated just the related sulfide 133. Treatment of 133 with a range of alcohols, 134-138, in the presence of N-iodosuccinimide and triflic acid, has given rise to intermediate disulfides, e. g. 139 in good yield and capable of reduction (Ra/Ni) to the 6,6 -dideoxy /3-disaccharide 140 [66]. This is truly an excellent result in terms of a direct synthesis of -acarbose. 

Nucleoside 5 -phosphorothioates have also been employed as activated nucleotide derivatives for synthesis of pyrophosphates.321 The interaction of tributylammonium 2, 3 -di-0-benzoyluridine 5 -phosphorothioate (73) with silver a-D-glucopyranosyl and a-D-galac-topyranosyl phosphates in pyridine solution, with subsequent de-benzoylation, gave the corresponding glycosyl esters in 60-70% yield. This procedure can probably be classified as a variant of the mixed-anhydride method, the driving force of the reaction being the formation of insoluble silver sulfide. 

Oligosaccharide Synthesis from Glycosyl Fluorides and Sulfides... 

G. Oligosaccharide synthesis from glycosyl fluorides and sulfides and the two-stage activation procedure 317... 

G. Oligosaccharide Synthesis from Glycosyl Fluorides and Sulfides and the Two-Stage Activation Procedure... 

The two-stage activation procedure for the synthesis of complex oligosaccharides developed in these laboratories [23] combines the chemistries of glycosyl fluorides and sulfides. It is, therefore, instructional to discuss first, the use of these two classes of glycosyl donors in oligosaccharide synthesis, before describing the two-stage activation method. 

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