N6-[(2-Azidoethoxy)carbonyl]-L-lysine hydrochloride (UAA crosslinker 1 hydrochloride) is a click chemistry-reactive amino acid derivative. N6-[(2-Azidoethoxy)carbonyl]-L-lysine hydrochloride mediates the generation of antibody-drug conjugates (ADCs). N6-[(2-Azidoethoxy)carbonyl]-L-lysine hydrochloride is used for site-specific incorporation into recombinant proteins, or for synthesizing chemical probes and tools for biological research.