2-Isobutoxy-1-isobutoxycarbonyl-1,2-dihydroquinoline, also known as IIDQ, is an amide coupling reagent utilised in liquid-phase synthesis. With IIDQ there is no need for the pre-activation step and the efficiency of the coupling is not influenced by the order of the addition of the reagents (amine, carboxylic acid, IIDQ). Furthermore, no guanidinium species are formed with IIDQ, and IIDQ is stable in presence of base. IIDQ is mainly applied in its polymer-supported form, polystyrene-supported IIDQ (PS-IIDQ), which is stable, reactive and efficient. PS-IIDQ requires a simpler purification compared to the free IIDQ and can be easily regenerated. Some applications of PS-IIDQ are in the synthesis of protein conjugates for antibody development and xanthine derivatives to be used as adenosine receptor antagonists.