Chemical (neo)glycosylation of biological drugs

Biological drugs, specifically proteins and peptides, are a privileged class of medicinal agents and are characterized with high specificity and high potency of therapeutic activity. However, biologics are fragile and require special care during storage, and are often modified to optimize their pharmacokinetics in terms of proteolytic stability and blood residence half-life. In this review, we showcase glycosylation as a method to optimize biologics for storage and application. Specifically, we focus on chemical glycosylation as an approach to modify biological drugs. We present case studies that illustrate the success of this methodology and specifically address the highly important question: does connectivity within the glycoconjugate have to be native or not? We then present the innovative methods of chemical glycosylation of biologics and specifically highlight the emerging and established protecting group-free methodologies of glycosylation. We discuss thermodynamic origins of protein stabilization via glycosylation, and analyze in detail stabilization in terms of proteolytic stability, aggregation upon storage and/or heat treatment. Finally, we present a case study of protein modification using sialic acid-containing glycans to avoid hepatic clearance of biological drugs. This review aims to spur interest in chemical glycosylation as a facile, powerful tool to optimize proteins and peptides as medicinal agents.

Applications of Shoda's reagent (DMC) and analogues for activation of the anomeric centre of unprotected carbohydrates

2-Chloro-1,3-dimethylimidazolinium chloride (DMC, herein also referred to as Shoda's reagent) and its derivatives are useful for numerous synthetic transformations in which the anomeric centre of unprotected reducing sugars is selectively activated in aqueous solution. As such unprotected sugars can undergo anomeric substitution with a range of added nucleophiles, providing highly efficient routes to a range of glycosides and glycoconjugates without the need for traditional protecting group manipulations. This mini-review summarizes the development of DMC and some of its derivatives/analogues, and highlights recent applications for protecting group-free synthesis.

Glycoconjugations of Biomolecules by Chemical Methods

Bioconjugations under benign aqueous conditions have the most promise to covalently link carbohydrates onto chosen molecular and macromolecular scaffolds. Chemical methodologies relying on C-C and C-heteroatom bond formations are the methods of choice, coupled with the reaction conditions being under aqueous milieu. A number of methods, including metal-mediated, as well as metal-free azide-alkyne cyclo-addition, photocatalyzed thiol-ene reaction, amidation, reductive amination, disulfide bond formation, conjugate addition, nucleophilic addition to vinyl sulfones and vinyl sulfoxides, native chemical ligation, Staudinger ligation, olefin metathesis, and Suzuki-Miyaura cross coupling reactions have been developed, in efforts to conduct glycoconjugation of chosen molecular and biomolecular structures. Within these, many methods require pre-functionalization of the scaffolds, whereas methods that do not require such pre-functionalization continue to be few and far between. The compilation covers synthetic methodology development for carbohydrate conjugation onto biomolecular and biomacromolecular scaffolds. The importance of such glycoconjugations on the functional properties is also covered.

Combining Click Reactions for the One-Pot Synthesis of Modular Biomolecule Mimetics

Here, we report on the first combined one-pot use of the two so-called "click reactions": the thiol-ene coupling and the copper-catalyzed alkyne-azide cycloaddition. These reactions were employed in an alternating and one-pot fashion to combine appropriately functionalized monomeric carbohydrate building blocks to create mimics of trisaccharides and tetrasaccharides as single anomers, with only minimal purification necessary. The deprotected oligosaccharide mimics were found to bind both plant lectins and human galectin-3.

Meet the Board of ChemistryOpen: Antony J. Fairbanks

Antony J. Fairbanks is a Professor in the Department of Chemistry at the University of Canterbury in New Zealand. The research of his group focuses on the broad areas of organic synthesis, particularly applied to carbohydrates. He currently serves as an active Editorial Board member for ChemistryOpen.