Selective Labeling of Living Cells by a Photo-Triggered Click Reaction.
Phototriggering of the metal-free azide to acetylene cycloaddn. reaction was achieved by masking the triple bond of dibenzocyclooctynes as cyclopropenone. Such masked cyclooctynes do not react with azides in the dark. Irradn. of cyclopropenones results in the efficient (Φ355 = 0.33) and clean regeneration of the corresponding dibenzocyclooctynes, which then undergo facile catalyst-free cycloaddns. with azides to give corresponding triazoles under ambient conditions. In situ light activation of a cyclopropenone linked to biotin made it possible to label living cells expressing glycoproteins contg. N-azidoacetyl-sialic acid. The cyclopropenone-based phototriggered click chem. offers exciting opportunities to label living organisms in a temporally and spatially controlled manner and may facilitate the prepn. of microarrays. [on SciFinder(R)]