Triazinium Ligation: Bioorthogonal Reaction of <i>N</i> 1‐Alkyl 1,2,4‐Triazinium Salts**
Veronika Šlachtová, Simona Bellová, Agustina La‐Venia, Juraj Galeta, Martin Dračínský, Karel Chalupský, Alexandra Dvořáková, Helena Mertlíková‐Kaiserová, Peter Rukovanský, Rastislav Dzijak, Milan Vrábel
Abstract
The development of reagents that can selectively react in complex biological media is an important challenge. Here we show that N1-alkylation of 1,2,4-triazines yields the corresponding triazinium salts, which are three orders of magnitude more reactive in reactions with strained alkynes than the parent 1,2,4-triazines. This powerful bioorthogonal ligation enables efficient modification of peptides and proteins. The positively charged N1-alkyl triazinium salts exhibit favorable cell permeability, which makes them superior for intracellular fluorescent labeling applications when compared to analogous 1,2,4,5-tetrazines. Due to their high reactivity, stability, synthetic accessibility and improved water solubility, the new ionic heterodienes represent a valuable addition to the repertoire of existing modern bioorthogonal reagents.