4-Ketobenzotriazine-CH2-S-(CH2)5-COOH

6-[(4-Oxo-1,2,3-benzotriazin-3-yl)methylthio]hexanoic acid (MBH) is a hapten with a carboxyl group at the end of its spacer arm, suitable for reacting with free amine groups of proteins. 6-[(4-Oxo-1,2,3-benzotriazin-3-yl)methylthio]hexanoic acid can be combined with carrier proteins and used in antigen design.