Biomimetic Tweezers for N-Glycans: Selective Recognition of the Core GlcNAc2 Disaccharide of the Sialylglycopeptide SGP

Synthetic molecular cage receptors for carbohydrate recognition

A captivating challenge in chemistry lies in achieving robust and precise binding of uncharged, hydrophilic carbohydrate entities. Although past decades have provided a variety of excellent molecular architectures tailored for carbohydrate recognition, including acyclic receptors, macrocycles and foldamers, recent advances have highlighted the potential of synthetic molecular cages. These structures are equipped with intricately designed cavities that contain bespoke noncovalent binding sites for carbohydrate interactions. Constructed with the principles of complementarity and preorganization, these cage receptors demonstrate high affinity and exquisite selectivity in carbohydrate recognition through noncovalent interactions, capitalizing on multivalency and cooperativity. This Review highlights recent advances in the design and application of molecular cages with diverse structures, interactions and binding capacities for carbohydrate recognition. In the concluding remarks, we discuss future avenues for further exploration.

From small changes to big gains: pyridinium-based tetralactam macrocycle for enhanced sugar recognition in water

The complex distribution of functional groups in carbohydrates, coupled with their strong solvation in water, makes them challenging targets for synthetic receptors. Despite extensive research into various molecular frameworks, most synthetic carbohydrate receptors have exhibited low affinities, and their interactions with sugars in aqueous environments remain poorly understood. In this work, we present a simple pyridinium-based hydrogen-bonding receptor derived from a subtle structural modification of a well-known tetralactam macrocycle. This small structural change resulted in a dramatic enhancement of glucose binding affinity, increasing from 56 M-1 to 3001 M-1. Remarkably, the performance of our synthetic lectin surpasses that of the natural lectin, concanavalin A, by over fivefold. X-ray crystallography of the macrocycle-glucose complex reveals a distinctive hydrogen bonding pattern, which allows for a larger surface overlap between the receptor and glucose, contributing to the enhanced affinity. Furthermore, this receptor possesses allosteric binding sites, which involve chloride binding and trigger receptor aggregation. This unique allosteric process reveals the critical role of structural flexibility in this hydrogen-bonding receptor for the effective recognition of sugars. We also demonstrate the potential of this synthetic lectin as a highly sensitive glucose sensor in aqueous solutions.

A Macrocyclic Tweezers-Shaped Receptor for the Biomimetic Recognition of the Gal(α1-3)Gal Disaccharide of the α-Gal Antigen

The Gal(α1-3)Gal is the terminal disaccharide unit of the α-Gal epitope [Gal(α1-3)Gal(β1-4)GlcNAc], an exogenous antigenic determinant with several clinical implications, found in all non-primate mammals and in several dangerous pathogens, including certain protozoa and mycobacteria. Its absence in humans makes the α-Gal epitope an interesting target for several infectious diseases. Here we present the development of a macrocyclic tweezers-shaped receptor, resulting from the combination of the structural features of two predecessors belonging to the family of diaminocarbazole receptors, which exhibits binding properties in the low millimolar range toward the Gal(α1-3)Gal disaccharide of the α-Gal antigen.

Towards Biomimetic Recognition of Glycans by Synthetic Receptors

Carbohydrates are abundant in Nature, where they are mostly assembled within glycans as free polysaccharides or conjugated to a variety of biological molecules such as proteins and lipids. Glycans exert several functions, including protein folding, stability, solubility, resistance to proteolysis, intracellular traffic, antigenicity, and recognition by carbohydrate-binding proteins. Interestingly, misregulation of their biosynthesis that leads to changes in glycan structures is frequently recognized as a mark of a disease state. Because of glycan ubiquity, carbohydrate binding agents (CBAs) targeting glycans can lead to a deeper understanding of their function and to the development of new diagnostic and prognostic strategies. Synthetic receptors selectively recognizing specific carbohydrates of biological interest have been developed over the past three decades. In addition to the success obtained in the effective recognition of monosaccharides, synthetic receptors recognizing more complex guests have also been developed, including di- and oligosaccharide fragments of glycans, shedding light on the structural and functional requirements necessary for an effective receptor. In this review, the most relevant achievements in molecular recognition of glycans and their fragments will be summarized, highlighting potentials and future perspectives of glycan-targeting synthetic receptors.