Separation of enantiomeric β-methyl amino acids and of β-methyl amino acid containing peptides

Abstract

Erythro- d,l- and threo- d,l-β-methylphenylalanine, -β-methyltyrosine and -β-methyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid were synthesized. High-performance liquid chromatographic methods were developed for the separation and identification of the enantiomers of the β-methyl amino acids, with the application of 1-fluoro-2,4-dinitrophenyl-5- l-alanine amide and 2,3,4,6-tetra-O-acetyl-β- d-glucopyranosyl isothiocyanate as derivatizing reagents. These amino acids were incorporated into the μ-agonist/δ-antagonist opioid peptides H-β-MeTyr-Tic-Phe-Phe-NH 2, H-Tyr-Tic-β-MePhe-Phe-NH 2 and H-Tyr-Tic-Phe-β-MePhe-NH 2, and the δ-antagonist H-Tyr-β-MeTic-Phe-Phe-OH, by solid-phase peptide synthesis. Each peptide has four stereoisomers. The peptide stereoisomers were separated on different columns and in different eluent systems and the elution order of the peptide epimers was determined.