Crudes of synthesis of neuropeptide Y and beta-amyloid peptide examined by liquid chromatography/electrospray tandem mass spectrometry.

The two peptides, neuropeptide Y (M(r) = 4254) and beta (1-39) amyloid (M(r) = 4230) are attracting pharmaceutical and biomedical interest for different yet equally important reasons. The first is recognized for its various physiological functions in the peripheral and central nervous system, while the second has been identified as one of the components of the cerebral amyloid deposits characteristic of Alzheimer's disease. High level purity of both peptides is considered of prime importance for correct interpretation of data obtained by biological and pharmaceutical assays and binding tests. Solid-phase synthesis of both peptides resulted in crudes of reaction containing both the target peptides as well as a number of undesired side products. The use of liquid chromatography/electrospray-tandem mass spectrometry (LC/ESI-MS/MS) furnished reliable information on the target peptides and provided sequencing information on a number of side products. Furthermore, LC/MS/MS data of doubly and triply protonated sequences yielded a number of C-terminal fragment ions exhibiting the loss of NH3 considered to be an important process for the understanding of fragmentation mechanism(s) of multiply protonated peptides.