Click-to-Release Reactions for Tertiary Amines and Pyridines

Click-to-release
reactions, transformations that liberate molecules
of interest under physiological conditions, are gaining traction as
powerful means to control biological processes and enable spatiotemporal
drug delivery. A major limitation of current click-to-release strategies
remains their narrow scope of releasable functional groups, leaving
many classes of bioactive molecules incompatible with such approaches.
This study provides the first examples of click-to-release reactions
for tertiary amines and pyridines. Two orthogonal strategies were
developed based on bioorthogonal reactions between isonitriles and
tetrazines. Isocyanopropyl (ICPr) groups were used to cage tertiary
amines and pyridines, enabling their release upon reaction with tetrazines
under mild conditions. Similarly, tetrazylmethyl (TzMe) groups masked
these functionalities for liberation by isonitriles. Interestingly,
while the removal of TzMe groups with primary isonitriles did not
occur as originally intended, tertiary isonitriles mediated efficient
release. Experimental and computational studies revealed an unexpected
pathway distinct from the previously reported mechanisms for TzMe
deprotection. The masking groups could be successfully applied to
a range of bioactive molecules, and the resulting precursors exhibited
good stability in the buffer. Preliminary studies in zebrafish embryos
established the bioorthogonality of the reactions. Together, this
work significantly expands the repertoire of releasable groups for
click-to-release chemistry and opens new opportunities for applications
in chemical biology and targeted drug delivery.