In this study, we have developed efficient strategies for the synthesis of glycosyl donors with 2-thioacetyl (SAc) groups in order to synthesize 2-deoxysugars with exclusive α/β-configuration. Starting from free methyl glycosides, four methyl 2-SAc glycosides were synthesized with high efficiency mainly through the double serial inversion strategy, and further turned into four corresponding 1-OAc, 2-SAc α-glycosyl donors (manno-, gluco-, galacto-and talo-types) and four corresponding 1-STol, 2-SAc 1,2-cis-glycosyl donors (manno-, gluco-, galacto-and talo-types). Glycosylation of the 1-OAc, 2-SAc donors and further 2-deoxysugar synthesis have also been investigated in this study.
A relatively
green method for synthesizing 1-thioalkyl glycosides
has been developed, where sodium alkanethiolates were used to react
with per-O-acetylated sugars instead of odorous alkyl mercaptans in
the presence of BF3·Et2O without the use
of solvents under mild conditions. Furthermore, we found that 1,2-trans-β-thioglycosides can be converted into corresponding
1,2-cis-α-thioglycosides in the presence of
trifluoromethanesulfonic acid in nonpolar solvents under mild conditions.
This provides a simple and efficient new approach for synthesizing
challenging 1,2-cis-α-thioglycosides.
In this study, we have successfully applied a visible-lightpromoted desulfurization method to the synthesis of deoxysugars, especially 1-deoxyglycose, 2,4-deoxyglycosides, and 2-deoxyglycosides with exclusive α-configuration. Compared to the reported desulfurization under UV light (500 W mercury lamp), this desulfurization under visible light (20 W blue LED) is easy to operate since it does not require a dedicated photochemical reactor, occurs under very mild conditions, and is able to avoid many of the side reactions that often occur during the UV-induced desulfurization.
Based on SnCl2‐catalyzed acetalation and selective benzoylation, a one‐pot strategy to efficiently synthesize orthogonally protected glycosyl acceptors with 2‐OH/3‐OH was developed. Consequently, 2‐OBz or 3‐OBz 4,6‐O‐benzylidene galactosides and glucosides were efficiently prepared in moderate to high yields starting from free galactosides and glucosides, and were used as valuable glycosyl acceptors for the synthesis of blood group antigens O and B analogues in this study.
Acetalization and deacetalation are a pair of routine manipulations to protect and deprotect the 4- and 6-hydroxyl groups of glycosides in the synthesis of glycosyl building blocks. In this study, we found that treatment of SnCl4 with various carbohydrates containing acetal/ketal groups with the assistance of water in CH2Cl2 led to deacetalization/deketalization products in almost quantitative yields. In addition, for substrates containing both acetal/ketal and p-methoxylbenzyl groups, we also found that the p-methoxylbenzyl group was selectively cleaved by the use of a catalytic amount of SnCl4, while the acetal/ketal groups remained. Furthermore, based on this, 4,6-benzylidene glycosides can be conveniently converted to 4,6-OAc or 4-OH, 6-OAc glycosides.
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