Solid-phase synthesis and characterization of N-methyl-rich peptides.
A library of peptides required for a project investigating the factors relevant for blood-brain barrier transport was synthesized on solid phase. As a result of the high N-methylamino acid content in the peptides, their syntheses were challenging and form the basis of the work presented here. The coupling of protected N-methylamino acids with N-methylamino acids generally occurs in low yield. (7-azabenzotriazol-1-yloxy)-tris(pyrrolidino)phosphonium hexafluorophosphate (PyAOP) or PyBOP/1-hydroxy-7-azabenzotriazole (HOAt), are the most promising coupling reagents for these couplings. When a peptide contains an acetylated N-methylamino acid at the N-terminal position, loss of Ac-N-methylamino acid occurs during trifluoroacetic acid (TFA) cleavage of the peptide from the resin. Other side reactions resulting from acidic cleavage are described here, including fragmentation between consecutive N-methylamino acids and formation of diketopiperazines (DKPs). The time of cleavage is shown to greatly influence synthetic results. Finally, high-performance liquid chromatography (HPLC) profiles of N-methyl-rich peptides show multiple peaks because of slow conversion between conformers.
Teixidó
M
M
Institut de Recerca Biomèdica de Barcelona, Parc Científic de Barcelona, Josep Samitier, Barcelona, Spain.
Albericio
F
F
Giralt
E
E
D000107:Acetylation; D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D001812:Blood-Brain Barrier / Q000378:metabolism; D006801:Humans; D008745:Methylation; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000737:chemistry; D019151:Peptide Library
D000596:Amino Acids; D009842:Oligopeptides; D019151:Peptide Library