Organo-zinc Promoted Diastereoselective C-Arylation of 1,2-Anhydrosugars from Arylboronic Acids

Diverse Synthesis of C-Glycosides by Stereoselective Ni-Catalyzed Carboboration of Glycals

C-Glycosides are important structures that are common to natural products and pharmaceutical agents. Established methods for their synthesis involve the reaction of an activated anomeric carbon. In this study, we report a conceptually new approach that involves the stereoselective Ni-catalyzed carboboration of glycals. In these reactions, not only is a C-C bond formed at the anomeric carbon, but a synthetically useful C-B bond is also installed. Upon C-B oxidation, differentially protected C-glycosides to be formed. In addition, stereospecific manipulation of the C-B bond leads to diverse C-glycosides. Finally, we report the application of this method in the synthesis of established C-glycosides, such as C-glycosyl amino acids, as well as a strategy to make all possible diastereomers at C1 and C2.

Stereoselective Construction of Orthogonally Protected, N-O Interlinked Disaccharide Mimetics Using N-Substituted β-Aminooxy Donors

Orthogonally protected N-substituted β-aminooxy sugars can be stereoselectively synthesized from sugar epoxides and nitrones derived from aromatic aldehydes. Both the ether- and ester-protected sugar epoxides can be employed. The synthesized aminooxy sugars could be reacted with aldehyde bearing/free reducing sugars under the heating condition to afford N-O-linked 1,1-/1,5/1,6-disaccharide mimetics in a good yield.

Diastereoselective synthesis of glycopyrans 1,2-annulated with dioxazinanes from 1,2-anhydrosugars and N-substituted nitrones

1,2-Annulated pyranose sugars fused with six membered rings have emerged as an important class of carbohydrates with wide biological and synthetic utility. We now describe zinc chloride catalyzed one pot diastereoselective synthesis of sugar fused dioxazinanes from 1,2-anhydro sugars and N-substituted aromatic nitrones. Various aromatic nitrones with different substituents undergo the reaction smoothly. The developed strategy works well with both ester and ether protection on the sugar and proceeds under mild reaction conditions. The mechanism seems to involve activation of the anhydrosugar by ZnCl₂ for nucleophilic attack by the nitrone followed by cyclization.

Modular and Stereoselective Synthesis of C-Aryl Glycosides via Catellani Reaction

In this work, we describe a Catellani-type C-H glycosylation to provide rapid access to various highly decorated α-C-(hetero)aryl glycosides in a modular and stereoselective manner (>90 examples). The termination step is flexible, which is demonstrated by ipso-Heck reaction, hydrogenation, Suzuki coupling, and Sonogashira coupling. Application of this methodology has been showcased by preparing glycoside-pharmacophore conjugates and a dapagliflozin analogue. Notably, the technology developed herein represents an unprecedented example of Catellani-type alkylation involving an S_N1 pathway.

Palladium catalysed carbonylation of 2-iodoglycals for the synthesis of C-2 carboxylic acids and aldehydes taking formic acid as a carbonyl source

Pd catalyzed carbonylative reaction of 2-iodo-glycals has been developed taking formic acid as a carbonyl source for the synthesis of 2-carboxylic acids of sugars by the hydroxycarbonylation strategy. The methodology was successfully extended to the synthesis of 2-formyl glycals by using a reductive carbonylation approach. Both ester and ether protected glycals undergo the reaction and furnished sugar acids in good yield which is otherwise not possible by literature methods. The C-2 sugar acids were successfully utilized for the construction of 2-amido glycals, 2-dipeptido-glycal by Ugi reaction and C-1 and C-2 branched glycosyl esters.

Synthesis of Sugar-Based Enones and Their Transformation into 3,5-Disubstituted Furans and 2-Acyl-Substituted 1,2,3-Trideoxy Sugars in the Presence of Lewis Acids

Pd-catalyzed carbonylative cross-coupling reactions of 2-iodoglycals have been developed for the synthesis of sugar-based arylones and ynones using formic acid as the carbonyl source. Whereas acetyl-protected arylones lead to the formation of highly substituted furan derivatives in the presence of Lewis acid, benzyl-protected arylones furnished the 3-deoxy sugar derivative. In the presence of nucleophiles, an attack took place on the C-1 or C-3 carbon regio- and stereoselectively depending on the nature of the nucleophiles.

Stereoselective synthesis of sugar-fused (or 1,2-annulated) isochromans and isochromanones by using oxa-Pictet-Spengler reaction

A highly efficient stereoselective synthesis of sugar fused 1,2-annulated isochromans is reported by utilizing the oxa-Pictet-Spengler cyclization reaction. The process is found to be very general as both glucal and galactal derived C2-hydroxy-α-C-aryl glycosides lead to the target molecules in good yields. The utility of this strategy was extended to the synthesis of sugar fused isochromanones, which are bergenin type molecules.

Cross dehydrogenative coupling of sugar enol ethers with terminal alkenes in the synthesis of pseudo-disaccharides, chiral oxadecalins and a conjugated triene

An efficient strategy for the synthesis of C-2 and C-3 branched sugar dienes via cross dehydrogenative coupling of sugar enol ethers with terminal alkenes was developed.

C-Glycopyranosyl Arenes and Hetarenes: Synthetic Methods and Bioactivity Focused on Antidiabetic Potential

This Review summarizes close to 500 primary publications and surveys published since 2000 about the syntheses and diverse bioactivities of C-glycopyranosyl (het)arenes. A classification of the preparative routes to these synthetic targets according to methodologies and compound categories is provided. Several of these compounds, regardless of their natural or synthetic origin, display antidiabetic properties due to enzyme inhibition (glycogen phosphorylase, protein tyrosine phosphatase 1B) or by inhibiting renal sodium-dependent glucose cotransporter 2 (SGLT2). The latter class of synthetic inhibitors, very recently approved as antihyperglycemic drugs, opens new perspectives in the pharmacological treatment of type 2 diabetes. Various compounds with the C-glycopyranosyl (het)arene motif were subjected to biological studies displaying among others antioxidant, antiviral, antibiotic, antiadhesive, cytotoxic, and glycoenzyme inhibitory effects.

Diastereoselective sp2–sp3 coupling of sugar enol ethers with unactivated cycloalkenes: new entries to C-branched sugars

Sugar enol ethers undergo efficient coupling at C-2 with unactivated cycloalkenes under a low Pd loading affording allylic substitution products. High diastereoselectivity was observed at the allylic centre with sterically hindered substrates.