Palladium-Catalyzed α‑Stereoselective <i>O</i>‑Glycosylation of O(3)‑Acylated Glycals

Pd­(MeCN)₂Cl₂ enables the α-stereoselective catalytic synthesis of 2,3-unsaturated <i>O</i>-glycosides from O(3)-acylated glycals without the requirement for additives to preactivate either donor or nucleophile. Mechanistic studies suggest that, unlike traditional (η3-allyl)­palladium-mediated processes, the reaction proceeds via an alkoxy-palladium intermediate that increases the proton acidity and oxygen nucleophilicity of the alcohol. The method is exemplified with the synthesis of a range of glycosides and glycoconjugates of synthetic utility

Gold(I)-Catalyzed Direct Stereoselective Synthesis of Deoxyglycosides from Glycals

Au­(I) in combination with AgOTf enables the unprecedented direct and α-stereoselective catalytic synthesis of deoxyglycosides from glycals. Mechanistic investigations suggest that the reaction proceeds via Au­(I)-catalyzed hydrofunctionalization of the enol ether glycoside. The room temperature reaction is high yielding and amenable to a wide range of glycal donors and OH nucleophiles

Nucleophilic Aromatic Substitution (S_NAr) as an Approach to Challenging Carbohydrate–Aryl Ethers

A general and practical route to carbohydrate–aryl ethers by nucleophilic aromatic substitution (S_NAr) is reported. Upon treatment with KHMDS, C–O bond formation occurs between carbohydrate alcohols and a diverse range of fluorinated (hetero)­aromatics to provide the targets in good to excellent yields. Commercially available arylating agents, high atom economy, and high regioselectivity are notable features of the protocol. The aryl ether products have potential for wide-ranging applications as exemplified by the synthesis of a novel chiral P,N-ligand

Stereoselective Glycosylation of 2‑Nitrogalactals Catalyzed by a Bifunctional Organocatalyst

The use of a bifunctional cinchona/thiourea organocatalyst for the direct and α-stereoselective glycosylation of 2-nitrogalactals is demonstrated for the first time. The conditions are mild, practical, and applicable to a wide range of glycoside acceptors with products being isolated in good to excellent yields. The method is exemplified in the synthesis of mucin type Core 6 and 7 glycopeptides

Is UV-Induced Electron-Driven Proton Transfer Active in a Chemically Modified A·T DNA Base Pair?

Transient electronic and vibrational absorption spectroscopies have been used to investigate whether UV-induced electron-driven proton transfer (EDPT) mechanisms are active in a chemically modified adenine–thymine (A·T) DNA base pair. To enhance the fraction of biologically relevant Watson–Crick (WC) hydrogen-bonding motifs and eliminate undesired Hoogsteen structures, a chemically modified derivative of A was synthesized, 8-(<i>tert</i>-butyl)-9-ethyladenine (8tBA). Equimolar solutions of 8tBA and silyl-protected T nucleosides in chloroform yield a mixture of WC pairs, reverse WC pairs, and residual monomers. Unlike previous transient absorption studies of WC guanine–cytosine (G·C) pairs, no clear spectroscopic or kinetic evidence was identified for the participation of EDPT in the excited-state relaxation dynamics of 8tBA·T pairs, although ultrafast (sub-100 fs) EDPT cannot be discounted. Monomer-like dynamics are proposed to dominate in 8tBA·T