New Synthetic Methods and Reagents for Complex Carbohydrates. VIII. Stereoselective α- and β-Mannopyranoside Formation from Glycosyl Dimethylphosphinothioates with the C-2 Axial Benzyloxyl Group

Abstract

The reactions of mannopyranosyl dimethylphosphinothioates and alcohols using silver perchlorate as an activator in the presence of molecular sieves 4A in benzene at room temperature gave the 1,2-trans-α-mannopyranosides in good yields. On the other hand, 1,2-cis-β-mannopyranosides could be obtained from the dimethylphosphinothioates by the combined use of iodine and 5 mol% triphenylmethyl perchlorate as an activating system. The syntheses of the derivatives of αMan(1→6)[αMan(1→3)]Man and βMan(1→4)GlcNAc units of glycoproteins by these methods are described.

General Aspects of the Glycosidic Bond Formation

“…Thus, the use of p-methoxybenzoyl (anisoyl) [91] and diethylthiocarbamoyl [81] groups was found to be exceptionally beneficial for the formation of a-galactosides. Similar effects (including C-3 participation) were also detected for the derivatives of the L-fuco [92,93], L-rhamno [94], D-manno and D-gluco [14,82,95] series [96]. It was noted that when the unprotected hydroxyl is present at C-4 of the sulfamidogalacto donor, the expected b-glycosyl formation occurs.…”

Stereocontrolled 1,2-cis glycosylation as the driving force of progress in synthetic carbohydrate chemistry

“…For derivatives of the d -galacto series a remote effect beneficial for the formation of α-galactosides was also noted when a participating moiety was present at C-4. 43 Similar effects (including C-3 participation) were also detected for the derivatives of the l -fuco, 44 l -rhamno, 45 d -manno, 46 and d -gluco 47 series.…”

A selective electrochemical method of glycosylation of 3β-hydroxy-Δ5-steroids

“…14 Various methods of glycosylation of steroids have been described. Glycosyl donors used among others were: glycosyl halides, 15 trihalogenoacetimidates, 16,17 thioglycosides, 18 1-O-sulfonyl glycosides, 19 glycals, 20 1-O-acyl sugars, 21 orthoesters or ethers, 22 phosphate derivatives, 23 1-O-silylated glycosides. 24 There are also known electrochemical methods of glycosylation, though they were not used for the preparation of steroidal glycosides.…”