Glycals and their Derivatives

Glycals are 1,2-unsaturated sugars having a C=C bond between C-1 and C-2 of the pyranose or furanose moieties of the carbohydrate scaffold. The presence of a C=C bond leads to enhanced reactivity. They are used as chiral building blocks in the synthesis of various natural products and medicinally significant molecules. There are numerous methods for the synthesis of exo-glycals and endo-glycals, such as glycosidations, reagent-based methods, and electrochemical methods. Glycals have shown their versatility and applicability in chemical synthesis in many ways e.g., epoxidation, cycloaddition, and formation of various glycosides like C-glycosides, Oglycosides, N-glycosides. They have also been employed in the synthesis of many biologically relevant natural products as starting materials.

Approximately 20 to 30 percent of all natural drugs are glycosylated, and the attached carbohydrate unit is pivotal for their biological activity. O- and S-glycosides constitute a significant portion of various biologically potent molecules and natural products. The synthesis of O- and S-glycosides holds immense importance due to several medicinal benefits. This chapter explores several methodologies for accessing O- and S-glycosides and the subsequent utilization of these glycosides for oligosaccharide generation. Specific pathways involved in O- and S-glycosides synthesis are discussed, along with detailed consideration of factors influencing the stereoselectivity of the desired products. 

A glycoside is recognized as a C-glycoside when the anomeric carbon of a sugar moiety is linked to an aglycone or another carbohydrate, creating a new C-C bond. Recently, C-glycosides have been recognized as a privileged class of carbohydrates owing to their extensive application in medicinal chemistry and drug discovery. These glycosides have played a vital role in designing various drug candidates owing to their stability towards acidic or enzymatic degradation. This chapter deals with the recent advances in the synthesis of privileged C-glycosides, including 2-deoxy-C-glycosides, using glycals and their derivatives.

The chemistry of glycals and their derivatives has emerged as a hot topic in carbohydrate chemistry owing to their incredible applications in biological and medicinal chemistry. Annulated and C-2-branched sugars derived from glycal moiety and its derivative have received immense attention. Herein, we have incorporated the current advancement in the synthesis of 2-C-branched sugars and annulated sugars derived from glycals, 2-haloglycals, and 2-nitroglycals using various synthetic strategies, including C-H activation, 1,2-annulation, and cyclopropanation.

Glycals have been widely used as a versatile building block for the synthesis of C-glycosides and branched sugars and the total synthesis of natural products and biologically active molecules. The versatility of glycals is due to their easy availability and the presence of a ring oxygen connected to a double bond. The inherent chirality of glycals also makes them valuable for the synthesis of various natural products and pharmaceuticals. This chapter provides a detailed overview of the progress made in synthesizing natural products and important molecules derived from glycals.