Synthesis of C3-Substituted N1-tert-Butyl 1,2,4-Triazinium Salts via the Liebeskind–Srogl Reaction for Fluorogenic Labeling of Live Cells

We recently described the development and application of new bioorthogonal conjugation, the triazinium ligation. To explore the wider application of this reaction, in this work we introduce a general method for synthesizing C3-substituted triazinium salts based on the Liebeskind–Srogl cross-coupling reaction and catalytic thioether reduction. These methods enabled the synthesis of triazinium derivatives for investigating the effect of different substituents on the ligation kinetics and stability of the compounds under biologically relevant conditions. Finally, we demonstrate that the combination of coumarin fluorophore attached to position C3 with a C5-(4-methoxyphenyl) substituent, yields a fluorogenic triazinium probes suitable for no-wash, live-cell labeling. The developed methodology represents a promising synthetic approach to the late-stage modification of triazinium salts, potentially widening their application in bioorthogonal reactions

Bicyclic N -dihalocyclopropylamide derivatives as precursors of nitrogen-containing fused polycyclic systems

International audienceExamples of carbon–carbon bond-forming cyclisation reactions, involving allyl cations generated by the thermal ring-opening of halocyclopropanes, have been scarcely reported. In this contribution, we are describing the results of a study conducted with N-dihalocyclopropylamide substrates, designed as precursors of cyclic iminium intermediates that were aimed at participating in intramolecular reactions with electron-rich aromatic groups. Competitive side-reactions were identified, and access to the desired polycyclic products was carefully evaluated. The results were found to be strongly dependent on the substitution pattern of the nucleophilic aromatic moieties, as well as on the sizes of the rings of the target products. In spite of the rather moderate yields generally obtained, this approach represents a particularly short and inexpensive route to various interesting nitrogen-containing polycyclic systems, namely benzoindolizidine, benzoquinolizidine, piperidinobenzoazepane and azepanoisoquinoline compounds

Triazinium Ligation: Bioorthogonal Reaction of N1-alkyl 1,2,4-Triazinium Salts

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, accessibility and improved water solubility, the new ionic heterodienes represent a valuable addition to the repertoire of existing modern bioorthogonal reagents