N-Butyryl-L-homoserine lactone (N-Butanoyl-L-homoserine lactone, N-Butyrylhomoserine lactone, C4-HSL) is a cleavable ADC linker applied into the synthesis of antibody-drug conjugates (ADCs). N-Butyryl-L-homoserine lactone is a small diffusible signaling molecule involved in quorum sensing, controlling gene expression, and cellular metabolism.