AuCl3-Catalyzed Hemiacetal Activation for the Stereoselective Synthesis of 2-Deoxy Trehalose Derivatives

Phenanthroline-Assisted Stereoselective Synthesis of 2-Deoxy Glycosides

The significance of 2-deoxy glycosides in biologically active compounds is well-established, as they frequently play a pivotal role in modulating the efficacy of therapeutic agents. The 2-deoxy sugar embodies a distinctive class of carbohydrates characterized by marked differences in stability, reactivity, and selectivity compared to their counterparts bearing C2-oxygen or other heteroatoms. As a result, the stereoselective synthesis of this carbohydrate class is complicated by its sensitivity to acidic conditions and propensity for hydrolysis and elimination reactions. Furthermore, the lack of C2-oxygen functionality presents an additional challenge in controlling stereoselectivity. In this study, we report the application of commercially available phenanthroline as an effective additive in the stereoselective glycosylation of aliphatic alcohols and phenolic nucleophiles with 2-deoxy glycosyl chlorides, facilitating efficient access to a variety of α-2-deoxy glycosides in high yields with synthetically useful stereoselectivity. Kinetic analyses suggest that phenanthroline plays a crucial role in modulating the selectivity of the reaction.

Origins of Selectivity in Glycosylation Reactions with Saccharosamine Donors

A combination of DFT calculations and experiments is used to describe how the selection of a promoter can control the stereochemical outcome of glycosylation reactions with the deoxy sugar saccharosamine. Depending on the promoter, either α- or β-linked reactive intermediates are formed. These studies show that differential modes of activation lead to the formation of distinct intermediates that undergo highly selective reactions through an SN2-like mechanism.

Iodine-triphenylphosphine triggers an easy one-pot alpha stereoselective dehydrative glycosylation on hemiacetalic benzylated glycosyl donors

The discovery of new glycosylation reactions is still a major challenge in carbohydrate chemistry. Traditional glycosylation reactions require the preparation of sugar donors with anomeric active or latent leaving groups. Dehydrative glycosylation is a fascinating alternative that enables the direct formation of the glycosidic bond from the hemiacetal, eliminating the need for (sometimes unstable) leaving groups, and allowing to reduce reaction, work-up, and purification times. Although some interesting methods of dehydrative glycosylation have been reported, in order to compete with conventional chemical glycosylation, a greater number of efficient and stereoselective methods need to be developed. Herein, a dehydrative procedure that uses a combination of iodine, triphenylphosphine, and a base (DMAP or imidazole) is described. This methodology allows for the preparation of sugar derivatives from commercially available 1-hydroxy glycosyl donors. The reaction takes place under mild conditions through the in situ-formation of an anomeric iodide intermediate, which, upon reaction with an alcohol, gives the corresponding glycosides up to quantitative yields and with high α-stereoselectivity.

Switchable reactivity of 2-benzoyl glycals towards stereoselective access of 1-3 and 1-1 S/O linked disaccharides

We have developed a synthesis of 1-3 and 1-1 disaccharides from 2-benzoyl glycal and anomeric thiol and/or hydroxy sugar acceptors under mild conditions at room temperature. The regio and stereo-selectivity of the newly formed inter-glycosidic linkages are dependent on the nature of the glycal donor (D or L) and anomeric acceptor.