Bioorthogonal Labeling, Bioimaging, and Photocytotoxicity Studies of Phosphorescent Ruthenium(II) Polypyridine Dibenzocyclooctyne Complexes

The synthesis, characterization, photophysics, lipophilicity, and cellular properties of new phosphorescent ruthenium(II) polypyridine complexes functionalized with a dibenzocyclooctyne (DIBO) or amine moiety [Ru(N^N)₂(L)](PF₆)₂ are reported (L=4-(13-N-(3,4:7,8-dibenzocyclooctyne-5-oxycarbonyl) amino-4,7,10-trioxa-tridecanyl-aminocarbonyl-oxy-methyl)-4′-methyl-2,2′-bipyridine bpy-DIBO, N^N=2,2′-bipyridine bpy (1a), 1,10-phenanthroline phen (2a); L=4-(13-amino-4,7,10-trioxa-tridecanylaminocarbonyl-oxy-methyl)-4′-methyl-2,2′-bipyridine bpy-NH₂, N^N=bpy (1b), phen (2b)). The strain-promoted alkyne-azide cycloaddition (SPAAC) reaction of the DIBO complexes 1a and 2a with benzyl azide were studied. Also, the DIBO complexes 1a and 2a can selectively label N-azidoglycans located on the surface of CHO-K1 and A549 cells that were pretreated with 1,3,4,6-tetra-O-acetyl-N-azidoacetyl-D-mannosamine (Ac₄ManNAz). Additionally, the intracellular trafficking and localization of these biomolecules were monitored using laser-scanning confocal microscopy. Interestingly, the biolabeling and cellular uptake efficiency of the DIBO complexes 1a and 2a were cell-line dependent, as revealed by flow cytometry and ICP-MS. Furthermore, the complexes showed good biocompatibility toward the Ac₄ManNAz-pretreated cells in the dark, but exhibited photoinduced cytotoxicity due to the generation of singlet oxygen.