Caged Cyclopropenes with Improved Tetrazine Ligation Kinetics

Abstract

Activatable cyclopropenes are unreactive toward their inverse electron demand Diels–Alder reaction partner (e.g., s-tetrazines) until they are activated. The activation strategy is highly modular due to the cyclopropene’s ability to be caged by various light- and enzyme-activatable groups. This work describes the next generation of activatable cyclopropenes with a new core scaffold that maintains the activation modularity of the first generation but improves upon the ligation kinetics with s-tetrazines by ≤270-fold.

Post‐Assembly Photomasking of Potassium Acyltrifluoroborates (KATs) for Two‐Photon 3D Patterning of PEG‐Hydrogels

“…Several groups have developed systems combining photoreactions with fast bioconjugation reactions [11–17] in hydrogels using photocaged hydroxylamines, [18] thiols [19–21] or cyclooctynes [22] that undergo deprotection and bioconjugation upon irradiation. This photocaging approach has been much rarer for other bioconjugation reactions such as tetrazine Diels–Alder or Staudinger reaction due to the lack of suitable photocaging methods [23,24] . Other alternative strategies to 3D photopatterning include enzymatic ligation of small peptide ligands [25–27] and photocatalyzed thiol‐ene [28–32] or CuAAC [33] reactions.…”

Photo‐induced and Rapid Labeling of Tetrazine‐Bearing Proteins via Cyclopropenone‐Caged Bicyclononynes

“…Forschungsartikel sfGFP-2-His6 and 11 is also significantly faster than reaction between 11 and as fGFP mutant bearing ap reviously described phenylalanine based tetrazine amino acid (TetF), [11b] which is presumably due to higher flexibility and on-protein accessibility of mTetK versus Te tF (Supporting Information, Figure S20). Thef ast kinetic rate constants enable photo-triggered labeling of mTetK-modified proteins with photo-11 within minutes at low mm or nm concentrations and put photo-iEDDAC reactions between DMBO and tetrazines among the fastest photo-induced bioorthogonal reactions,s everal orders of magnitude faster than recently described approaches with caged cyclopropenes (k 2 % 10 À2 -10 À4 m À1 s À1 ), [17] and considerably faster than most photo-SPAACr eactions with strained dibenzocyclooctynes (k 2 % 10 À1 -10 À2 m À1 s À1 ), [30] and on par with the recently described and so far fastest photo-SPAACr eaction employing photooxa-dibenzocylooctyne (k 2 % 40 m À1 s À1 ). [31]…”

“…[12] Key advances include light-triggered tetrazole-alkene photoclick chemistry, [13] visible-light induced [4+ +2] cycloaddition between 9,10-phenanthrenequinone and vinyl ethers [14] as well as photo-induced activation of cyclopropenone-caged cyclooctynes for strain-promoted azide-alkyne cycloadditions (photo-SPAAC). [17] As the former approach is so far limited to dihydrotetrazines that are stable to spontaneous air oxidation, and photo-induced iEDDAC with described caged cyclopropenes show very slow reaction rates (k 2 % 10 À2 -10 À4 m À1 s À1 ), there is however apressing need for novel, photo-inducible iEDDAC reactions with fast kinetics. [17] As the former approach is so far limited to dihydrotetrazines that are stable to spontaneous air oxidation, and photo-induced iEDDAC with described caged cyclopropenes show very slow reaction rates (k 2 % 10 À2 -10 À4 m À1 s À1 ), there is however apressing need for novel, photo-inducible iEDDAC reactions with fast kinetics.…”

“…[15] Importantly,a lso versions of photo-induced iEDDAC have been reported, such as light/enzymetriggered redox-activation of dihydrotetrazines to tetrazines [16] and the modular caging of cyclopropenes. [17] As the former approach is so far limited to dihydrotetrazines that are stable to spontaneous air oxidation, and photo-induced iEDDAC with described caged cyclopropenes show very slow reaction rates (k 2 % 10 À2 -10 À4 m À1 s À1 ), there is however apressing need for novel, photo-inducible iEDDAC reactions with fast kinetics.…”

Enabling in vivo Photocatalytic Activation of Rapid Bioorthogonal Chemistry by Repurposing Si-Rhodamine Fluorophores as Cytocompatible Far-Red Photocatalysts

“…47 The bioorthogonal Diels-Alder reactions of tetrazines with strained alkene and alkyne dienophiles has become increasingly important to the chemical biology community due to their exceptional kinetics with rates that can exceed 10 6 M -1 s -1 with conformationally strained trans-cyclooctenes. [48][49][50][51] Recent interest in the development of photochemically inducible variants of tetrazine ligation have prompted the discovery of new methods for uncaging cyclopropene 52,53 and bicyclononyne 28 dienophiles. Tetrazine (Tz) synthesis is commonly achieved through the oxidation of dihydrotetrazine (DHTz) precursors, 54 and the DHTz/Tz redox couple has been used in electrochemically controlled bioconjugation at electrode surfaces, 55 in batteries, 56 and for colorimetric nitrous gas detection.…”