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.