Amino acid bioconjugation via iClick reaction of an oxanorbornadiene-masked alkyne with a Mn(I)(bpy)(CO)3-coordinated azide.

The catalyst-free room temperature iClick reaction of an unsymmetrically 2,3-disubstituted oxanorbornadiene (OND) as a "masked" alkyne equivalent with [Mn(N3)(bpy(CH3,CH3))(CO)3] leads to isolation of a phenylalanine ester bioconjugate, in which the model amino acid is linked to the metal moiety via a N-2-coordinated triazolate formed in a cycloaddition-retro-Diels-Alder (crDA) reaction sequence, in a novel approach to bioorthogonal coupling reactions based on metal-centered reactivity.