Stable, Reactive, and Orthogonal Tetrazines: Dispersion Forces Promote the Cycloaddition with Isonitriles

• Published in: Angewandte Chemie 2019-07, Vol.131 (27), p.9141-9146
• Main Authors: Tu, Julian, Svatunek, Dennis, Parvez, Saba, Liu, Albert C., Levandowski, Brian J., Eckvahl, Hannah J., Peterson, Randall T., Houk, Kendall N., Franzini, Raphael M.
• Format: Article
• Language: English
• Subjects: Alkenes; Alkynes; Biokonjugation; Bioorthogonale Chemie; Chemistry; Chemoselektivität; Computer applications; Cycloaddition; Cycloadditionen; Dispersion; Dispersionskräfte; Functional groups; Labeling; Rate constants
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201903877

The isocyano group is a structurally compact bioorthogonal functional group that reacts with tetrazines under physiological conditions. Now it is shown that bulky tetrazine substituents accelerate this cycloaddition. Computational studies suggest that dispersion forces between the isocyano group and the tetrazine substituents in the transition state contribute to the atypical structure–activity relationship. Stable asymmetric tetrazines that react with isonitriles at rate constants as high as 57 L mol−1 s−1 were accessible by combining bulky and electron‐withdrawing substituents. Sterically encumbered tetrazines react selectively with isonitriles in the presence of strained alkenes/alkynes, which allows for the orthogonal labeling of three proteins. The established principles will open new opportunities for developing tetrazine reactants with improved characteristics for diverse labeling and release applications with isonitriles. Wählerische Tetrazine: Hochstabile Tetrazine, die schnell mit Isonitrilen reagieren, wurden hergestellt. Sperrige Tetrazinsubstituenten wechselwirken sterisch vorteilhaft mit der Isocyangruppe im Übergangszustand der Cycloaddition und blockieren die Annäherung gespannter Alkene. Diese Merkmale ermöglichen eine rasche bioorthogonale Markierung und Freisetzung. Damit gelang die orthogonale Markierung dreier Proteine.