2-Propanephosphonic acid anhydride (T3P)-mediated segment coupling and head-to-tail cyclization of sterically hindered peptides

In the course of comparing the effectiveness of an HOAt-derived coupling re agent (HAPyU) and a phosphonic acid-based condensation agent (T3P) by cycli zation of model sequences, we found that T3P was a superior reagent with re gard to conversion of the linear peptide into the stereochemically intact c yclic monomer when sterically hindered amino acids are found at the cycliza tion site.