Increased understanding of the important roles that oligosaccharides and glycoconjugates play in biological processes has led to a demand for significant amounts of these materials for biological, medicinal, and pharmacological studies. Therefore, tremendous effort has been made to develop new procedures for the synthesis of glycosides, whereby the main focus is often the formation of the glycosidic bonds. Accordingly, quite a few review articles have been published over the past few years on glycoside synthesis; however, most are confined to either a specific type of glycoside or a specific strategy for glycoside synthesis. In this Review, new principles for the formation of glycoside bonds are discussed. Developments, mainly in the last ten years, that have led to significant advances in oligosaccharide and glycoconjugate synthesis have been compiled and are evaluated.

New principles for glycoside-bond formation.

Advances in the chemical synthesis of C-pyranosides/furanosides are summarized, covering the literature from 2000 to 2016. The majority of the methods take advantage of the construction of the glycosidic C—C bond. These C-glycosylation methods are categorized herein in terms of the glycosyl donor precursors, which are commonly used in O-glycoside synthesis and are easily accessible to nonspecialists. They include glycosyl halides, glycals, sugar acetates, sugar lactols, sugar lactones, 1,2-anhydro sugars, thioglycosides/sulfoxides/sulfones, selenoglycosides/telluroglycosides, methyl glycosides, and glycosyl imidates/phosphates. Mechanistically, C-glycosylation reactions can involve glycosyl electrophilic/cationic species, anionic species, radical species, or transition-metal complexes, which are discussed as subcategories under each type of sugar precursor. Moreover, intramolecular rearrangements, such as the Claisen rearrangement, Ramberg–Backlund rearrangement, and 1,2-Wittig rearrangement, which usuall...

Recent Advances in the Chemical Synthesis of C-Glycosides

Solid acids: Green alternatives for acid catalysis

Catalytic glycosylation has been a central reaction in carbohydrate chemistry since its introduction by Fischer 125 years ago, but it is only in the past three to four decades that catalytic methods for synthesizing oligosaccharides have appeared. Despite the development of numerous elegant and ingenious catalytic glycosylation methods, only a few are in general use. This review covers all methods of catalytic glycosylation with the focus on the development and application in oligosaccharide synthesis and provide an overview of the scope and limitations of these. The review also includes relevant mechanistic studies of catalytic glycosylations. The future of catalytic glycosylation chemistry is discussed, including specific, upcoming methods and possible directions for the field of research in general.

Catalytic Glycosylations in Oligosaccharide Synthesis

Highly efficient, one-pot, four-component synthesis of 1,2,4,5-tetrasubstituted imidazoles was reported the condensation of various aldehydes, benzil, aliphatic or aromatic primary amines and ammonium acetate under solvent free conditions using perchloric acid adsorbed on silica gel (HClO 4 –SiO 2 ) as catalyst in excellent yields. HClO 4 –SiO 2 exhibited remarkable catalytic activity with respect to the reaction time (2–20 min), amount of catalyst. Present protocol with HClO 4 –SiO 2 catalyst is convincingly superior to the recently reported catalytic methods.

Highly efficient, one-pot, solvent-free synthesis of tetrasubstituted imidazoles using HClO4–SiO2 as novel heterogeneous catalyst

Alkyl 2,3-unsaturated glycopyranosides have been prepared by the Ferrier rearrangement of acetyl protected glycals catalyzed by HClO 4 -SiO 2 . Operational simplicity, use of economically convenient catalyst, mild reaction conditions, high yields, short reaction times are the key features of this protocol.

Ferrier Rearrangement Catalyzed by HClO4-SiO2: Synthesis of 2,3-Unsaturated Glycopyranosides

One-pot synthesis of per-O-acetylated thioglycosides from unprotected reducing sugars.

Direct one-pot conversion of acylated carbohydrates into their alkylated derivatives under heterogeneous reaction conditions using solid NaOH and a phase transfer catalyst.

Geetanjali Agnihotri

Papers

Ferrier Rearrangement Catalyzed by HClO4-SiO2: Synthesis of 2,3-Unsaturated Glycopyranosides

One-pot synthesis of per-O-acetylated thioglycosides from unprotected reducing sugars.

Direct one-pot conversion of acylated carbohydrates into their alkylated derivatives under heterogeneous reaction conditions using solid NaOH and a phase transfer catalyst.

Mild and efficient method for the cleavage of benzylidene acetals using HClO4-SiO2 and direct conversion of acetals to acetates

Nitric Acid Mediated Oxidative Transformation of Thiols to Disulfides