Scheme 2

Protein polyfunctionalization and labeling by the P-3C bioconjugation. A Derivatization of BSA with multiple isocyanide groups and subsequent multicomponent fluorescent labeling. B ESI-TOF mass spectra of native BSA and isocyano-BSAs 12a and 14. C Characterization of the fluorescently labeled BSA 15 and 16 by SDS-PAGE with Coomassie staining and in-gel fluorescence scanning in comparison with a negative control BSA(C-) prepared by incubating BSA with carboxyfluorescein under the same reaction conditions.