Sglycosides

S-glycosides, also known as thioglycosides, are glycosides in which the anomeric carbon of a sugar is linked to an aglycone through a sulfur atom, forming a thio-glycosidic bond. The sugar moiety can be any standard pyranose or furanose, such as glucose, galactose, or mannose, and the linkage at the anomeric center can be either alpha or beta, depending on stereochemistry and protecting groups.

In structure, thioglycosides resemble ordinary O-glycosides but feature a sulfur atom at the glycosidic bond. The C1–S bond is typically less prone to certain hydrolytic pathways and can be selectively activated under mild conditions to form glycosidic bonds with alcohols, phenols, or other nucleophiles. The reactivity of a thioglycoside as a glycosyl donor can be tuned by changing the protecting groups on the sugar and by the thiol component of the aglycone.

Preparation of S-glycosides usually involves forming a thioglycoside from a protected sugar derivative and a thiol partner. Common routes include thiolation of a protected sugar with a thiol or displacing a glycosyl halide or glycosyl imidate with a thiol. In practice, thioglycosides are often prepared as stable glycosyl donors for subsequent activation.

Applications of S-glycosides are most prominent in carbohydrate chemistry and oligosaccharide synthesis. They serve as versatile glycosyl donors that can be activated by promoters such as N-iodosuccinimide with catalytic acids or other Lewis acids to construct complex glycosidic linkages. They also provide useful building blocks for protective-group strategies and studies of glycosylation mechanisms. See also glycoside, thioglycoside, glycosylation.