Chemoselective methionine bioconjugation with alkyne-bearing oxaziridine and alkyne-bearing iodonium salts was investigated as a new platform for site-selective radiolabeling of proteins and peptides with fluorine-18. Alkyne-bearing sulfimide conjugates, resulting from oxaziridine modification, underwent copper-assisted alkyne-azide cycloaddition (CuAAC) with an F-labeled PEGylated azide to afford F-labeled triazoles in excellent radiochemical yields. Diazoester sulfonium salt bioconjugates, formed from alkyne-bearing 2-diazoiodonium salts, gave low yields of F-labeled triazoles and were shown to be unstable to CuAAC conditions. Photolytic removal of the diazo group, however, afforded the trialkylsulfonium salt which smoothly underwent CuAAC with the F-labeled PEGylated azide to afford high radiochemical yields of the desired F-labeled click product. Overall, the results establish the viability of chemoselective methionine bioconjugation as a method for preparing site-selective F-labeled PET radioligands.

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http://dx.doi.org/10.1021/acs.bioconjchem.0c00256DOI Listing

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