Heterogeneous energy-transfer metallaphotocatalysis unlocks direct and site-selective thioglycosylation of unprotected thiosugars

The creation of glycoconjugates, particularly well-defined glycopeptides, is crucial for advancing biological research and therapeutic development. However, the direct and selective coupling of unprotected thioglycosides to native biomolecules remains a formidable challenge due to the incompatibility of conventional synthetic methods with the delicate and complex functional groups present in these molecules. Here, we report a heterogeneous metallaphotocatalytic strategy that addresses this limitation through an energy-transfer mechanism. By embedding nickel catalytic centers within a photoactive covalent organic framework, we create a system that directly excites transient thiosugar-nickel complexes, thereby bypassing the high activation barriers inherent to conventional redox pathways. This approach enables site-selective and stereocontrolled thioglycosylation under mild, operationally simple conditions, featuring a high turnover frequency (114 per hour) and exceptional catalyst recyclability. The broad scope of the method is demonstrated through the glycosylation of diverse substrates, including amino acids and bioactive peptides, without the need for protecting groups. Notably, this method enables the first heterogeneous photocatalytic glycosylation of an antimicrobial peptide mastoparan, enhancing its antitumor activity. This work provides a versatile and sustainable tool for precision bioconjugation, offering immediate potential in drug discovery and chemical biology.