Isolation, identification, and characterization of a palladium complex in the catalytic deprotection of a protected peptide

The final catalytic deprotection in the large scale synthesis of thymopentin (Arg‐Lys‐Asp‐Val‐Tyr) produced an impurity which had not previously been observed. Isolation by preparative HPLC and spectroscopic characterization led to a postulated structure of the impurity as the 1: 1 thymopentin‐palladium complex. A complex corresponding to the proposed structure was independently synthesized and shown to have identical chromatographic and spectroscopic properties with the isolated material. Proton and carbon (13) NMR were used to determine the coordination sites of the peptide with palladium. The susceptibility of the complex to hydrogenation indicated a possible source for its formation.