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Metabolic oligosaccharide engineering is a valuable tool to monitor cellular carbohydrates. Here, we report the synthesis of a novel N-acyl-mannosamine derivative bearing a methylcyclopropene tag that is attached to the sugar via a carbamate moiety. This derivative undergoes rapid Diels-Alder reaction with inverse electron demand. We demonstrate that the cell's biosynthetic machinery incorporates this non-natural mannosamine derivative into glycoconjugates that can, subsequently, be labeled within less than 10 min with a new sulfo-Cy3-tetrazine conjugate. Using this tetrazine-dye conjugate for the detection of the methylcyclopropene-tagged mannosamine derivative, we could achieve dual labeling of two different metabolically incorporated sugars combining a Diels-Alder reaction with inverse electron demand and a strain-promoted azide-alkyne cycloaddition which are carried out simultaneously in a single step.
Dunn et al. (1979) studied this question.