| Abstract: | Abstract We have been interested in the synthesis of branched peptides, by grafting an amine, eg histamine, to the carboxylic group of aspartic acid side chain of Boc-β Ala-Trp-Met-Asp-Phe-NH2 also called Pentagastrin (or α-PG). Depending on the coupling conditions used, the main product obtained might be either the wanted derivative or a side-product identified a6 amino-succinyl-pentagastrin (or ASC-PG). Acid or base treatment of this product cleaved the amino-succinyl ring and yielded either α-PG or/and (β-Aspartyl)4-PC or β-PG. Amino-succinylation being a general problem in peptide synthesis of aspartyl residue containing peptides, synthesis of α-PG, β-PG, Asc-PG and their corresponding C-terminal dipeptide amides were performed to be analyzed by mass spectroscopy. FAB mass spectra (PI in glycerol) of the free peptides, as well as of their N-Boc derivatives have been recorded and compared to the mono, di, tri and tetra peptide derivatives. The pseudo-molecular ions of Boc-peptides are usually not observed. However, the intense M+1-Boc (? 100 u) ions are present. Several sequence ions have been identified and compared to the simulation of their spectra according to six fragmentation routes. The identification of α, β or succinimide structures from FAB spectra has been proposed. |
