ASYMMETRIC HYDROGENATION OF UNSATURATED PEPTIDES

Abstract
Eleven unsaturated peptides, containing one or two dehydro‐phenylalanyl (dehydro‐Phe) residues and a C‐terminal L‐amino acid have been hydrogenated in the presence of palladium‐on‐charcoal.Hydrolysis of the saturated peptides thus obtained gave optically active phenylalanine showing the occurrence of asymmetric induction during the hydrogenation.Both mono‐unsaturated dipeptides and doubly unsaturated tripeptides with L‐Glu, L‐Leu and L‐Val as chiral end‐group afforded L‐Phe in 40–50% optical yield. In the case of the tripeptide N‐acetyl‐(dehydro‐Phe)‐(dehydro‐Tyr)‐L‐Glu the asymmetric induction was higher (70%) for the unsaturated residue which is farther from the chiral end‐group along the peptide chain.The results are discussed on the bases of Prelog rule and the rigid dissymmetric conformation of the dehydropeptides in solution.

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