Synthesis of sugar enones and their use as powerful synthetic precursors of thiodisaccharides

Monosaccharide derivatives having a double bond conjugated to a carbonyl (sugar enones or enuloses) are relevant synthetic tools. They are also suitable starting materials, or versatile intermediates, for the synthesis of a wide variety of natural or synthetic compounds with a broad spectrum of biological and pharmacological activities. The preparation of enones is mainly focused on the search for more efficient and diastereoselective synthetic methodologies. The usefulness of enuloses relies on the diverse reaction possibilities offered by alkene and carbonyl double bonds, which are prone to undergo varied reactions such as halogenation, nitration, epoxidation, reduction, addition, etc. The addition of thiol groups that led to sulfur glycomimetics, such as thiooligosaccharides, is particularly relevant. Therefore, the synthesis of enuloses and the Michael addition of sulfur nucleophiles to give thiosugars or thiodisaccharides are discussed here. Chemical modifications of the conjugate addition products to afford biologically active compounds are also reported.

Photooxidation of thiosaccharides mediated by sensitizers in aerobic and environmentally friendly conditions

A series of β-d-glucopyranosyl derivates have been synthesized and evaluated in photooxidation reactions promoted by visible light and mediated by organic dyes under aerobic conditions. Among the different photocatalysts employed, tetra-O-acetyl riboflavin afforded chemoselectively the respective sulfoxides, without over-oxidation to sulfones, in good to excellent yields and short reaction times. This new methodology for the preparation of synthetically useful glycosyl sulfoxides constitutes a catalytic, efficient, economical, and environmentally friendly oxidation process not reported so far for carbohydrates.