Stereoselective glycosylation of endo-glycals by microwave- and AlCl3-assisted catalysis

Ferrier/Aza-Wacker/Epoxidation/Glycosylation (FAWEG) Sequence to Access 1,2-Trans 3-Amino-3-deoxyglycosides

3-Amino-3-deoxyglycosides constitute an essential class of nitrogen-containing sugars. Among them, many important 3-amino-3-deoxyglycosides possess a 1,2-trans relationship. In view of their numerous biological applications, the synthesis of 3-amino-3-deoxyglycosyl donors giving rise to a 1,2-trans glycosidic linkage is thus an important challenge. Even though glycals are highly polyvalent donors, the synthesis and reactivity of 3-amino-3-deoxyglycals have been little studied. In this work, we describe a new sequence, involving a Ferrier rearrangement and subsequent aza-Wacker cyclization that allows the rapid synthesis of orthogonally protected 3-amino-3-deoxyglycals. Finally a 3-amino-3-deoxygalactal derivative was submitted for the first time to an epoxidation/glycosylation with high yield and great diastereoselectivity, highlighting FAWEG (Ferrier/Aza-Wacker/Epoxidation/Glycosylation) as a new approach to access 1,2-trans 3-amino-3-deoxyglycosides.

A Comprehensive Biological and Synthetic Perspective on 2-Deoxy-d-Glucose (2-DG), A Sweet Molecule with Therapeutic and Diagnostic Potentials

Glucose, the primary substrate for ATP synthesis, is catabolized during glycolysis to generate ATP and precursors for the synthesis of other vital biomolecules. Opportunistic viruses and cancer cells often hijack this metabolic machinery to obtain energy and components needed for their replication and proliferation. One way to halt such energy-dependent processes is by interfering with the glycolytic pathway. 2-Deoxy-d-glucose (2-DG) is a synthetic glucose analogue that can inhibit key enzymes in the glycolytic pathway. The efficacy of 2-DG has been reported across an array of diseases and disorders, thereby demonstrating its broad therapeutic potential. Recent approval of 2-DG in India as a therapeutic approach for the management of the COVID-19 pandemic has brought renewed attention to this molecule. The purpose of this perspective is to present updated therapeutic avenues as well as a variety of chemical synthetic strategies for this medically useful sugar derivative, 2-DG.

Rhenium(V)-catalyzed synthesis of 1,1'-2-deoxy thioglycosides

As stable glycomimetics, thioglycosides are important tools for the investigation of biological processes and discovery of new drugs. In this note, we report a ReOCl3(SMe2)(OPPh3) catalyzed coupling reaction between β-glycosyl thiols (1-thio sugars) and glycals for the preparation of 1,1'-α,β-2-deoxy thioglycosides, which are glycomimetics of natural trehalose and 2-deoxy glycosides. Furthermore, an S-linked trisaccharide was successfully obtained by successive employment of the Re(V) catalyzed thioglycosylation protocol.

Copper(ii)-catalyzed stereoselective 1,2-addition vs. Ferrier glycosylation of "armed" and "disarmed" glycal donors

Selective activation of "armed' and ''disarmed" glycal donors enabling the stereo-controlled glycosylations by employing Cu(ii)-catalyst as the promoter has been realized. The distinctive stereochemical outcome in the process is mainly influenced by the presence of diverse protecting groups on the donor and the solvent system employed. The protocol is compatible with a variety of aglycones including carbohydrates, amino acids, and natural products to access deoxy-glycosides and glycoconjugates with high α-anomeric selectivity. Notably, the synthetic practicality of the method is amply verified for the stereoselective assembling of trisaccharides comprising 2-deoxy components. Mechanistic studies involving deuterated experiments validate the syn-diastereoselective 1,2-addition of acceptors on the double bond of armed donors.

Cd(ii) coordination compounds as heterogeneous catalysts for microwave-assisted peroxidative oxidation of toluene and 1-phenylethanol

Cd(ii) compounds as catalysts towards microwave assisted peroxidative oxidation (with tert-butylhydroperoxide, TBHP) of toluene and 1-phenylethanol under heterogeneous conditions are explored.

Cooperative Brønsted Acid-Type Organocatalysis for the Stereoselective Synthesis of Deoxyglycosides

A practical approach for the α-stereoselective synthesis of deoxyglycosides using cooperative Brønsted acid-type organocatalysis has been developed. The method is tolerant of a wide range of glycoside donors and acceptors, and its versatility is exemplified in the one-pot synthesis of a trisaccharide. Mechanistic studies suggest that thiourea-induced acid amplification of the chiral acid via H-bonding is key for the enhancement in reaction rate and yield, while stereocontrol is dependent on the chirality of the acid.

TMSBr-mediated solvent- and work-up-free synthesis of α-2-deoxyglycosides from glycals

The thio-additions of glycals were efficiently promoted by a stoichiometric amount of trimethylsilyl bromide (TMSBr) to produce S-2-deoxyglycosides under solvent-free conditions in good to excellent yields. In addition, with triphenylphosphine oxide as an additive, the TMSBr-mediated direct glycosylations of glycals with a large range of alcohols were highly α-selective.

A 3,4-trans-fused cyclic protecting group facilitates α-selective catalytic synthesis of 2-deoxyglycosides

A practical approach has been developed to convert glucals and rhamnals into disaccharides or glycoconjugates with high α-selectivity and yields (77-97%) using a trans-fused cyclic 3,4-O-disiloxane protecting group and TsOH⋅H2O (1 mol%) as a catalyst. Control of the anomeric selectivity arises from conformational locking of the intermediate oxacarbenium cation. Glucals outperform rhamnals because the C6 side-chain conformation augments the selectivity.