Design of Spiro[2.3]hex-1-ene, a Genetically Encodable Double-Strained Alkene for Superfast Photoclick Chemistry

Reactive yet stable alkene reporters offer a facile route to studying fast biological processes via the cycloaddition-based bioorthogonal reactions. Here, we report the design and synthesis of a strained spirocyclic alkene, spiro[2.3]­hex-1-ene (Sph), for an accelerated photoclick chemistry, and its site-specific introduction into proteins via amber codon suppression using the wild-type pyrrolysyl-tRNA synthetase/tRNACUA pair. Because of its high ring strain and reduced steric hindrance, Sph exhibited fast reaction kinetics (k2 up to 34 000 M–1 s–1) in the photoclick chemistry and afforded rapid (<10 s) bioorthogonal protein labeling.