PyAOP ((7-Azabenzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate) is a coupling reagent used in solid phase peptide synthesis. It is a derivative of the HOAt family of coupling reagents. It is preferred over HATU, because it does not side react at the N-terminus of the peptide. Compared to the HOBt derivates, PyAOP (and HOAt in general) are more reactive due to the additional nitrogen.