In the vast and intricate world of biomolecules, carbohydrates stand out not only for their ubiquity but also for their complex structural diversity. These molecules are indispensable to life, serving fundamental roles in energy storage, cellular communication, and molecular recognition processes. Among the myriad forms carbohydrates assume, glycosides represent a crucial class, characterized by a glycosidic bond linking sugar units to other molecules. Traditionally, O-glycosides, where this linkage involves oxygen, have dominated biochemical pathways. However, a rising star within carbohydrate chemistry is the C-glycoside, where the oxygen atom in the glycosidic bond is substituted with carbon, conferring distinct chemical and biological properties.
C-glycosides have garnered extensive attention due to their enhanced stability against enzymatic degradation. Such resistance is particularly desirable in medicinal chemistry, where drug molecules must often withstand metabolic breakdown to exert their therapeutic effects. Notably, C-aryl glycosides exemplify this class through their incorporation of aromatic carbon frameworks directly bonded to the sugar moiety. These structures have culminated in the development of influential pharmaceuticals, most prominently inhibitors of the sodium-glucose cotransporter-2 (SGLT2) such as dapagliflozin, canagliflozin, and empagliflozin. These molecules have revolutionized the management of type 2 diabetes, offering patients improved glycemic control with favorable safety profiles.
Despite their pharmacological significance, the synthetic access to C-aryl glycosides remains challenging. Conventional synthetic routes have historically relied on protected sugar intermediates to control reactivity and selectivity during glycosylation, resulting in extended multi-step sequences. These processes often involve elaborate protecting-group strategies that add complexity and reduce overall yield. Most traditional methods also depend on classical cross-coupling reactions, such as Suzuki or Stille couplings, which frequently face issues with selectivity, substrate scope, and stereochemical control—critical factors given the chiral nature of carbohydrate scaffolds.
In a remarkable leap forward, a new methodology now offers a streamlined and versatile pathway to C-aryl glycosides by exploiting glycosyl sulfonyl hydrazides as radical precursors in redox-neutral cross-coupling reactions. This approach circumvents the need for protecting groups and harsh reaction conditions, utilizing unprotected native sugars as starting materials. Under mild conditions, these specially designed glycosyl hydrazides undergo controlled homolytic cleavage to generate glycosyl radicals, which subsequently engage in cross-coupling with aryl partners to construct C–C bonds directly at the anomeric center of carbohydrates.
The radical-based strategy presents multiple advantages. Redox neutrality obviates the requirement for external oxidants or reductants, simplifying reaction setups and minimizing byproducts. The ability to generate glycosyl radicals from readily accessible hydrazides derived from free sugars represents a practical innovation, enabling rapid synthesis of diverse C-aryl glycoside derivatives with high efficiency and stereoselectivity. This methodology exhibits an unprecedented breadth of scope, accommodating a variety of aryl electrophiles and tolerating a wide array of functional groups.
One of the most compelling demonstrations of this chemistry lies in the synthesis of all the clinically approved SGLT2 inhibitors. By applying this radical cross-coupling technique, the researchers accomplished direct coupling of sugar scaffolds to their requisite aryl groups without the conventional encumbrances of protection and multiple purification steps. This advancement not only streamlines the synthesis but also expands the potential for rapid analog development and optimization in pharmaceutical contexts.
Beyond the anomeric position, this platform enables C–C bond formation at multiple sites on the carbohydrate framework. Such versatility empowers synthetic chemists to functionalize sugars in novel ways, creating a diverse array of glyco-conjugates and chemical probes with improved or previously inaccessible pharmacological properties. The stereoretentive nature of the radical coupling is particularly noteworthy, as it can override intrinsic stereochemical preferences of substrates, facilitating access to rare or unnatural carbohydrate stereoisomers valuable in drug discovery.
The implications of this work extend to natural product synthesis as well. Complex glycosides such as salmochelins and neopetrosins, known for their biological activities, can now be assembled with greater efficiency and precision. This could accelerate research into glycosylated natural products, often challenging due to their multifunctional and stereochemically rich structures. Access to these compounds may deepen our understanding of their mechanisms of action and broaden therapeutic application.
Moreover, this approach catalyzes the design of medicinally relevant molecular probes that incorporate carbohydrate motifs, serving as tools to interrogate carbohydrate-related biological pathways or deliver drugs with improved targeting and bioavailability. The method’s modularity and mild reaction conditions make it amenable to late-stage functionalization, preserving delicate molecular architectures while enabling structural diversification.
From a mechanistic perspective, the generation and controlled reactivity of glycosyl radicals in the presence of sulfonyl hydrazides underpins the success of this platform. Radical translocation and coupling steps occur stereoselectively, underscoring the intricate balance of kinetics and thermodynamics achievable through precise reagent design. Such understanding opens avenues for further methodological innovations aimed at expanding radical-based carbohydrate chemistry.
Importantly, the entire synthetic sequence benefits from operational simplicity and scalability, key considerations for industrial application. By eliminating protecting groups and minimizing purification steps, this protocol promises to lower production costs and environmental impact, aligning with green chemistry principles. For pharmaceutical manufacturers, such advances could translate to faster drug development timelines and more sustainable processes.
This breakthrough exemplifies the convergence of classical carbohydrate chemistry and contemporary radical-based synthetic methodologies. It reflects the ongoing evolution in chemical synthesis wherein strategic harnessing of radical intermediates furnishes access to molecules of high complexity with unprecedented efficiency and control. As a result, the field of glycoscience stands poised to unlock new frontiers in drug design, chemical biology, and beyond.
In conclusion, the deployment of glycosyl sulfonyl hydrazides as redox-neutral radical precursors heralds a new era in C-glycoside synthesis. This innovation overcomes longstanding hurdles in carbohydrate modification, enabling rapid, selective, and practical construction of pharmaceutically relevant glycosylated architectures. It is not merely an advancement in synthetic methodology but a transformative platform with profound implications for medicinal chemistry, natural product synthesis, and biochemical research.
Subject of Research: C-glycoside synthesis and carbohydrate radical cross-coupling
Article Title: C-glycoside synthesis via radical cross-coupling of glycohydrazides
Article References:
Guo, Y., Li, Y., Buchberger, B. et al. C-glycoside synthesis via radical cross-coupling of glycohydrazides. Nature (2026). https://doi.org/10.1038/s41586-026-10807-x
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