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. Author manuscript; available in PMC: 2020 Mar 1.
Published in final edited form as: Curr Protoc Chem Biol. 2019 Jan 15;11(1):e61. doi: 10.1002/cpch.61

Figure 6:

Figure 6:

Activation of a C-terminal peptide hydrazide through acid-catalyzed acyl pyrazole formation: the Knorr Pyrazole Synthesis. The C-terminal peptide pyrazole is rapidly exchanged to the arylthioester species for use in NCL by reaction with 4-mercaptophenylacetic acid (MPAA).