Side reactions in solid phase synthesis of histidine-containing peptides. Characterization of two major impurities by sample displacement chromatography and FAB-MS.

The flow-polyamide synthesis of a histidine-containing sequence (Ac-YDNVLDHLTGR) produced two major impurities which were isolated through Sample Displacement Chromatography and characterized by Fast Atom Bombardment-mass analysis. The impurities correspond to the sequence Ac-YDNVLDH, and to a peptide with the Asp residue cyclized to a succinimide. The latter side-reaction took place during the acetylation procedure, and demands attention where capping procedures are planned in the synthesis of Asp-His sequences.