Strain-promoted reaction of 1,2,4-triazines with bicyclononynes.
Strain-promoted inverse electron-demand Diels-Alder cycloaddition (SPIEDAC) reactions between 1,2,4,5-tetrazines and strained dienophiles, such as bicyclononynes, are among the fastest bioorthogonal reactions. However, the synthesis of 1,2,4,5-tetrazines is complex and can involve volatile reagents. 1,2,4-Triazines also undergo cycloaddition reactions with acyclic and unstrained dienophiles at elevated temperatures, but their reaction with strained alkynes has not been described. We postulated that 1,2,4-triazines would react with strained alkynes at low temperatures and therefore provide an alternative to the tetrazine cycloaddition reaction for use in in vitro or in vivo labelling experiments. We describe the synthesis of a 1,2,4-triazin-3-ylalanine derivative fully compatible with the fluorenylmethyloxycarbonyl (Fmoc) strategy for peptide synthesis and demonstrate its reaction with strained bicyclononynes at 37 °C with rates comparable to the reaction of azides with the same substrates. The synthetic route to triazinylalanine is readily adaptable to late-stage functionalization of other probe molecules, and the 1,2,4-triazine-SPIEDAC therefore has potential as an alternative to tetrazine cycloaddition for applications in cellular and biochemical studies.
School of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, Woodhouse Lane, LS2 9JT Leeds (UK).
Katherine A
KA
Horner
School of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, Woodhouse Lane, LS2 9JT Leeds (UK).
Nathalie M
NM
Valette
School of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, Woodhouse Lane, LS2 9JT Leeds (UK). m.e.webb@leeds.ac.uk.
Michael E
ME
Webb
bioorthogonal chemistry; chemical biology; strain-promoted reactions; synthetic methods; triazines