Luminescent alkyne-bearing terbium(III) complexes and their application to bioorthogonal protein labeling

Two new bifunctional macrocyclic chelate ligands that form luminescent terbium(III) complexes featuring an alkyne group for conjugation to (bio)molecules via the Cu(I)-catalyzed "click" reaction were synthesized. Upon ligation, the complexes exhibit a significant luminescent enhancement when excited at the λ_max of the "clicked" products. To demonstrate the utility of the complexes for luminescent labeling, they were conjugated in vitro to E. coli aspartate/glutamate-binding protein incorporating a genetically encoded p-azido-l-phenylalanine or p-(azidomethyl)-l-phenylalanine residue. The complexes may prove useful for time-gated assay applications.