The coupling reaction is the critical step in peptide synthesis. In particular, the solid-phase approach relies on rapid peptide bond formation and complete conversion with a minimum of concomitant side-reactions such as racemization.
To meet these requirements a plethora of coupling (activation) reagents has been developed and employed since the early days of peptide synthesis. Coupling reagents (not forgetting the by-products formed during the coupling) have to fulfil additional requirements to be used in solid-phase synthesis, such as rapid dissolution and high solubility in DMF or NMP, stability in solid form as well as in solution, low toxicity and allergenicity. This last need triggered the development of a range of non-allergenic, environmentally safe and highly effective reagents, one of the most recent products being COMU.
Due to its structure COMU can be used with merely one equivalent of DIPEA, which makes it a perfect choice for the activation of base-sensitive amino acid derivatives. Yet COMU turned out to be more efficient than TBTU – it showed a coupling efficiency comparable to that of HATU. COMU and its by-product ethyl 2-cyano-2-hydroxyiminoacetate are stable under normal working and shipping conditions contrary to the potentially explosive HOBt and HOBt-based coupling reagents BOP or TBTU. The water-solubility of this iminoacetate is an additional advantage of COMU, broadening the scope of potential applications.
Nevertheless, ‘classical’ coupling agents such as EDC and EEDQ are still in use. They have found special applications in which they surpass other reagents, e.g. solid-phase peptide synthesis in aqueous systems or the derivatization of silica to obtain column material for chiral HPLC.
- Q-1980 – BOP
- Q-2735 – COMU
- Q-2565 – 3-(Diethoxy-phosphoryloxy)-1,2,3-benzo[d]triazin-4(3H)-one (DEPBT)
- Q-1735 – EEDQ
- Q-1955 – N-Ethyl-N’-(3-dimethylaminopropyl)-carbodiimide, HCl (EDC, HCl)
- Q-2600 – 2-(1-Oxy-pyridin-2-yl)-1,1,3,3-tetramethylisothiouronium tetrafluoroborate (TOTT)
- Q-2715 – PyBOP
- Q-1665 – TBTU
- Q-2280 – TFFH
For additional information on these and many other reagents and amino acid derivatives for peptide synthesis and modification please visit our website.