Click-Addressable Cassette for Photoaffinity Labeling.

A small molecule 1 was designed to contain an alkyne, a trifluoromethyl phenyldiazirine, and a free piperidine-NH for facile conjugation to protein binding ligands. This "cassette" 1 was synthesized via a relatively direct route involving only routine steps. In this proof-of-concept study, putative ligands for carbonic anhydrase IX and for TrkC were conjugated to 1. Photoaffinity labeling was performed using purified extracellular regions of both these protein-receptors, and using cells that express these receptors (isolation via a pull-down procedure), labeling of the protein was observed in all four experiments.