Coupling and Linking agents for Peptide Synthesis. It is important to select the most appropriate coupling reagent in solid-phase and solution peptide synthesis for the compound you are synthesising. They all have strengths and weaknesses depending on the structure you are trying to create. This is why we have such a broad selection of compounds. From the original coupling reagents used as activators (Carbodiimides), to more recent classes, the phosphonium based coupling agents and the uronium based reagents. Importantly these newer coupling agents exhibit very high rates of coupling and low rates of cross-reaction. Examples are BOP, COMU, HBTU, HATU, PyBOP, PyBrOP, TBTU, and TFFH.