Peptide-Catalyzed Conversion of Racemic Oxazol-5(4H)-ones into Enantiomerically Enriched α-Amino Acid Derivatives
摘要:
We report the development and optimization of a tetrapeptide that catalyzes the methanolytic dynamic kinetic resolution of oxazol-5(4H)-ones (azlactones) with high levels of enantioinduction. Oxazolones possessing benzylic-type substituents were found to perform better than others, providing methyl ester products in 88:12 to 98:2 er. The mechanism of this peptide-catalyzed process was investigated through truncation studies and competition experiments. High-field NOESY analysis was performed to elucidate the solution-phase structure of the peptide, and we present a plausible model for catalysis.
(Z)-2-N-Acylamino-3-thienyl-acrylic acids and their esters were prepared by known procedures and hydrogenated to the corresponding optically active 2-N-acetyl(or benzoyl)-3-(2- or 3-thienyl)-alanines with optical yields up to 90 % using the rhodium complexes of ''PROPRAPHOS'' 6a,b and O,N-bis(diphenylphosphino)-2-exo-hydroxy,3-endo-methylamino-norbornane 6c as chiral catalysts, Recrystallization and deacylation of the obtained amino acid derivatives yields the optically pure hydrochlorides of the thienylalanines and the free amino acids.