Carbohydrate synthesis sits at the heart of modern drug discovery and chemical biology. Sugars and sugar-like scaffolds appear in antiviral nucleoside analogues, antibiotic natural products such as the gilvocarcins, and a wide range of glycosylated therapeutics. Yet assembling these molecules from scratch has always been difficult. The classic formose reaction, discovered by Alexander Butlerov in 1861 and later elucidated by Ronald Breslow, can generate sugars from formaldehyde, but it produces complex, uncontrolled mixtures. More refined approaches, including the catalytic asymmetric aldol chemistry developed by MacMillan, Wong and others, and the tandem biocatalytic methods reported more recently, still require multiple sequential operations, careful protecting-group management, or enzymatic systems limited to particular substrates.

The central obstacle to a truly iterative, carbonylation-based route to sugars has been what the authors describe as cumulative catalyst deactivation and stereochemical drift. Each carbon monoxide insertion in a cascade adds a new carbon unit and creates a new stereocentre, but as the chain grows, the reactive intermediates become progressively harder to control. Catalysts that perform well in the first insertion may falter in the second or third, and the stereochemical information installed early in the sequence can be eroded before the reaction reaches its endpoint. Previous formal triple-carbonylation reactions, such as the cobalt-catalysed transformation of epoxy alcohols reported by Alper and colleagues in 1990, hinted at the potential of the concept but never delivered a general route to defined carbohydrate products.

The new method hinges on three interlocking design elements. First, precise control of the hydrosilane stoichiometry ensures that the three carbon monoxide insertions occur in kinetic synchrony, so that each reactive intermediate is consumed as soon as it forms rather than accumulating and decomposing. Second, careful ligand selection on the rhodium catalyst tunes the rates of the individual insertion steps, keeping the cascade on a single productive pathway. Third, a silicon-directed cyclization terminates the sequence: the silyl ether installed during the cascade acts as an internal handle that directs ring closure to the furanose architecture, converting a growing acyclic chain into a stable, isolable sugar product.

Stereochemical control, the make-or-break feature of any sugar synthesis, is achieved through what the researchers term a chelation-relay mechanism. As each carbon monoxide unit is inserted, the growing chain coordinates to the metal centre in a way that relays stereochemical information from one centre to the next, propagating a defined three-dimensional arrangement across three contiguous stereocentres. The result is good diastereocontrol, meaning that the products emerge predominantly as single stereoisomers rather than mixtures, a prerequisite for any method intended to feed pharmaceutical discovery, where the biological activity of a sugar derivative can depend entirely on the spatial arrangement of its hydroxyl groups.

The substrate scope is strikingly broad. The authors demonstrate that the cascade tolerates aldehydes ranging from simple aromatic substrates to complex steroidal aldehydes, suggesting that the method can be applied not only to model systems but to real, functionally dense molecules drawn from natural product and medicinal chemistry contexts. This breadth matters because a sugar-building method is only as useful as the molecules it can decorate; a route restricted to benzaldehyde derivatives would be of academic interest alone, whereas one that accepts steroidal aldehydes opens the door to rapid assembly of glycoconjugates and sugar-modified drug candidates.

The synthetic utility of the products is showcased through a series of downstream transformations. The threofuranose scaffolds can be elaborated into N-glycosides and C-glycosides, two classes of compounds of intense pharmaceutical relevance. C-glycosides, in which the sugar is linked to an aglycone through a robust carbon-carbon bond, resist enzymatic cleavage and appear in numerous drug candidates, as reviewed extensively in the chemical literature. The products also serve as entry points to nitrogen heterocycles and polyol motifs, the oxygenated carbon frameworks that recur throughout bioactive natural products. In effect, the cascade delivers a versatile, stereochemically rich platform from which medicinal chemists can branch in multiple directions.

Mechanistic studies underpin the design. The authors draw on decades of precedent in rhodium-catalysed carbonylation chemistry, including the silylformylation of aldehydes first reported by Murai and Sonoda in 1979 and developed by Wright and Cochran, in which hydrosilanes and carbon monoxide combine to extend aldehydes by one carbon. The new work extends that logic across three consecutive insertions, a feat requiring that the catalyst survive repeated cycles of oxidative addition, migratory insertion and reductive elimination without losing activity. Crystallographic data deposited at the Cambridge Crystallographic Data Centre confirm the structures of key products, providing unambiguous evidence for the stereochemical outcomes that the chelation-relay mechanism predicts.

The broader significance of the work lies in its reframing of carbonylation chemistry as a platform for assembling oxygen-rich scaffolds, not merely for installing individual carbonyl groups. Carbon monoxide has long been a workhorse of industrial chemistry, powering hydroformylation processes discovered by Wilkinson and collaborators in the 1960s and more recent achievements such as palladium-catalysed routes to adipic acid esters and non-equivalent diamides. Using CO as a one-carbon building block for carbohydrate construction, however, is a conceptual leap: it suggests that the carbon skeletons of sugars, and perhaps other polyhydroxylated natural products, could be assembled programmatically from aldehyde feedstocks and carbon monoxide, bypassing the extractive sources of sugars that dominate current practice.

For the pharmaceutical industry, the implications are immediate. Nucleoside analogue drugs, including remdesivir, whose development against Ebola virus was reported by Warren and colleagues, depend on precisely constructed sugar cores, and de novo routes to such cores, exemplified by MacMillan’s short synthesis of nucleoside analogues, have transformed access to these molecules. A one-step carbonylative route to threofuranose frameworks offers a complementary and potentially faster entry to related scaffolds, particularly for four-carbon sugar systems such as the alpha-threofuranosyl oligonucleotides explored in the chemical etiology of nucleic acid structure by Schöning and colleagues. With a patent application on the methodology already granted to Sun Yat-Sen University, the triple-carbonylation cascade now stands as a candidate technology for scale-up, and as an invitation for chemists to imagine carbohydrate synthesis not as a sequence of protected intermediates but as a single, catalytically orchestrated cascade from the simplest of starting materials.

Subject of Research: Rhodium-catalysed triple-carbonylation cascade converting aldehydes into stereochemically defined threofuranose sugars

Article Title: De novo synthesis of threofuranoses via a triple-carbonylation cascade of aldehydes

Article References: Shen, X., Nie, R., Jiang, W., & Li, S. (2026). De novo synthesis of threofuranoses via a triple-carbonylation cascade of aldehydes. Nature Chemistry. https://doi.org/10.1038/s41557-026-02258-8

Image Credits: AI Generated

DOI: 10.1038/s41557-026-02258-8

Keywords: threofuranoses, triple carbonylation, rhodium catalysis, aldehydes, carbohydrate synthesis, carbon monoxide, chelation-relay mechanism, C-glycosides, stereoselective synthesis, hydrosilane, Nature Chemistry, novo