Alkene–Tetrazine Ligation for Imaging Cellular DNA


  • We gratefully acknowledge the Swiss National Science Foundation (146754 to N.W.L.) and the University of Zürich Forschungskredit (FK-13-113 to U.R.) for financial support. We thank Dr. Kathrin Lang and Prof. Dr. Jason Chin for providing the fluorescent tetrazine “Tamra-Tz”. We thank Dr. Anne B. Neef, Dr. Kai J. Neelsen and Therese Triemer for helpful discussions.


5-Vinyl-2′-deoxyuridine (VdU) is the first reported metabolic probe for cellular DNA synthesis that can be visualized by using an inverse electron demand Diels–Alder reaction with a fluorescent tetrazine. VdU is incorporated by endogenous enzymes into the genomes of replicating cells, where it exhibits reduced genotoxicity compared to 5-ethynyl-2′-deoxyuridine (EdU). The VdU–tetrazine ligation reaction is rapid (k≈0.02 M−1 s−1) and chemically orthogonal to the alkyne–azide “click” reaction of EdU-modified DNA. Alkene–tetrazine ligation reactions provide the first alternative to azide–alkyne click reactions for the bioorthogonal chemical labeling of nucleic acids in cells and facilitate time-resolved, multicolor labeling of DNA synthesis.