Bond-Breaking Bio-orthogonal Chemistry Efficiently Uncages Fluorescent and Therapeutic Compounds under Physiological Conditions.

Bond-breaking bio-orthogonal chemistry, consisting of a "click" reaction between trans-cyclooctene and tetrazine, followed by an intramolecular cyclization-driven uncaging step is described. The two-step process allows activation of caged compounds in biological media at neutral pH. The feasibility of this chemistry has been illustrated using NMR, while kinetics and pH-dependence were studied by fluorescence spectroscopy using caged coumarin. The practicality of the strategy is illustrated by activation of an anticancer drug, etoposide.