Hydrazonyl Sultones as Stable Tautomers of Highly Reactive Nitrile Imines for Fast Bioorthogonal Ligation Reaction

• Published in: Journal of the American Chemical Society 2023-05, Vol.145 (18), p.9959-9964
• Main Authors: Fang, Ming, Kumar, Gangam Srikanth, Racioppi, Stefano, Zhang, Heyang, Rabb, Johnathan D., Zurek, Eva, Lin, Qing
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.2c12325

Here we report the design and synthesis of a new class of bioorthogonal reagents called hydrazonyl sultones (HS) that serve as stable tautomers of highly reactive nitrile imines (NI). Compared to the photogenerated NI, HS display a broad range of aqueous stability and tunable reactivity in a 1,3-dipolar cycloaddition reaction, depending on substituents, sultone ring structure, and solvent conditions. DFT calculations have provided vital insights into the HS → NI tautomerism, including a base-mediated anionic tautomerization pathway and a small activation barrier. Comparative kinetic analysis of tetrazole vs HS-mediated cycloadditions reveals that a tiny fraction of the reactive NI (∼15 ppm) is present in the tautomeric mixture, underpinning the extraordinary stability of the six-membered HS. We further demonstrate the utilities of HS in selective modification of bicyclo[6.1.0]­non-4-yn-9-ylmethanol (BCN)-lysine-containing nanobodies in phosphate buffered saline and fluorescent labeling of a BCN-lysine-encoded transmembrane glucagon receptor on live cells.