DBCO-NHS ester 3 (Compound 12) is a cleavable linker utilized in the synthesis of antibody-drug conjugate (ADC). It is a derivative of Dibenzylcyclooctyne (DBCO) resulting from the activation of N-hydroxysuccinimide by the carboxylic acid moiety of both methyl-oxanorbornadiene (MeOND) and dibenzoazacyclooctyne (DIBAC)[1][2].