Catalytic Uncaging of Anticancer Drugs via a Buchner Ring Expansion

Abstract Selective drug activation in living systems remains a central challenge in targeted cancer therapy. Bioorthogonal catalysis addresses this by using abiotic transition-metal catalysts to unmask prodrugs at the tumor site, but the repertoire of suitable reactions remains limited. Here, we exploit the Buchner ring-expansion as a new uncaging strategy, in which a metal-carbene catalyzes a regioselective intramolecular ring-expansion followed by spontaneous 1,6-elimination to release a caged payload─a cascade with no biological equivalent. The iridium porphyrin complex [Ir(mPIX)Me] catalyzes this reaction at nanomolar concentrations, and the platform can accommodate structurally diverse payloads. As a proof of concept, functionalization with a bivalent human carbonic anhydrase IX (hCA IX) inhibitor enabled tumor-selective release of epirubicin (Epi) in a cancer cell model. This work thus delineates a new reaction class to the growing toolkit of transition-metal-mediated bioorthogonal chemistry.