A new tag reagent for efficient capping and easy separation of deletion peptides

N-(Biphenyl-4-carbonyl)-l-proline was tested as a new capping reagent. The reagent was successfully used in the synthesis of the classic difficult sequence, acyl carrier protein (65–74). Analytical RP-HPLC with on line ESI-MS detection was used to analyse the unpurified cleavage products. The crude peptide was eluted as a single peak at 16.7 min. In the ESI mass spectrum of this peak a major ion is observed at m/z 1063.9 that corresponds to the complete protonated molecular ion [M+H]+. The molecular mass of the truncated des-Val65 nonapeptide contaminant is not present. Due to both its reactivity and its lipophilic nature, N-(biphenyl-4-carbonyl)-l-proline can be used as a tag for the deletion peptides in the sequence dependent difficult synthesis and in the automated synthesis of a longer peptide, facilitating the purification of the target peptide.