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. Author manuscript; available in PMC: 2015 Dec 14.
Published in final edited form as: Org Biomol Chem. 2014 Oct 15;12(46):9307–9320. doi: 10.1039/c4ob01632g

Fig. 14.

Fig. 14

Smart tetrazine conjugates containing flexible linkers and well-suited for imaging alkenes in biological systems. (A) BODIPY-tetrazine conjugate 32. As the tetrazine is consumed by cycloaddition to form 33, FRET quenching is relieved and fluorescence is restored. (B) A tetramethylrhodamine-tetrazine conjugate. (C) Carboxyfluorescein diacetate-tetrazine conjugate 35. The acetates are cleaved by intracellular esterases to reveal the free fluorescein 36. Spectroscopic properties correspond to cycloaddition products of the corresponding tetrazine probes.