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. Author manuscript; available in PMC: 2022 Apr 15.
Published in final edited form as: Nat Rev Methods Primers. 2021 Apr 15;1:30. doi: 10.1038/s43586-021-00028-z

Fig. 4 |. Cycloaddition-based bioorthogonal chemical reaction types.

Fig. 4 |

a | Strained alkynes enable copper-free catalysis of cycloaddition to dipoles such as azides. b | The fastest biorthogonal reaction involves the inverse-electron demand [4 + 2] addition between a tetrazine and a dienophile. BARAC, biarylazacyclooctynone; BCN, bicyclo[2.1.0]nonyne; DIBO, dibenzocyclooctyne; DIFO, difluorinated cyclooctyne; k2, second-order rate constant; OCT, cyclooctyne; TMTH, 3,3,6,6-tetramethylthiaheptyne.