N3-D-Orn(Boc)-OH (CHA) is a Boc-protected valine derivative utilized as a click chemistry reagent in the synthesis of antibody-drug conjugates (ADC). It contains an Azide group that can undergo copper-catalyzed Azide-Alkyne Cycloaddition (CuAAc) with molecules containing Alkyne groups. Additionally, it can engage in Strain-Promoted Azide-Alkyne Cycloaddition (SPAAC) with molecules possessing DBCO or BCN groups.