DBCO-C6-Acid (or ADIBO/DIBAC) is a non-activated building block commonly used for synthesis of complex molecules for copper-free Click Chemistry reactions. Primary or secondary amines can react with DBCO groups in the presence of activators (e.g. EDC, HATU), forming a stable amide bond. The extended 6-carbon long spacer arm makes this reagent more soluble in commonly used organic solvents (e.g. dichloromethane, chloroform, THF, ethyl acetate) and also greatly improves coupling efficiency and stability of conjugates.