title: The cis-trans isomerization of N-methyl-α,β-dehydroamino acids.
abstract: Dehydroamino acids with the methylated N-terminal peptide group occur in natural small cyclic peptides. The structural analysis was used to investigate the cis-trans isomerization of the N-terminal tertiary amide group of diamides: Ac-(Z)-Δ(Me)Abu-NHMe (1), Ac-(Z)-Δ(Me)Phe-NHMe (2), Ac-(E)-Δ(Me)Phe-NHMe (3), Ac-Δ(Me)Ala-NHMe (4), and Ac-(Me)Ala-NHMe (5). The compounds were analyzed in the solid state by an X-ray crystallography (1-3), and in the solution by FTIR (MeCN and CHCl(3) ) and NMR (DMSO-d6 and CDCl(3) ) methods (1-5). In the solid state, the studied compounds adopt the cis configuration of N-terminal amide. In solution, this configuration also prevails for the dehydroamino acids 1-4, in contrast to the saturated analog 5. The results indicate that N-methyldehydroamino acids present a promising tool to induce the cis configuration of the amide bond.
authors.affiliation: Faculty of Chemistry, University of Opole, Oleska 48, Opole 45-052, Poland. dsiodlak@uni.opole.pl
authors.forename: Dawid
authors.initials: D
authors.lastname: Siodłak
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Macedowska-Capiga
authors.forename: Małgorzata A
authors.initials: MA
authors.lastname: Broda
authors.forename: Anna E
authors.initials: AE
authors.lastname: Kozioł
authors.forename: Tadeusz
authors.initials: T
authors.lastname: Lis
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D000143:Acids / Q000737:chemistry*; D000577:Amides / Q000737:chemistry*; D002725:Chloroform / Q000737:chemistry; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013237:Stereoisomerism
chemical_list: D000097:Acetonitriles; D000143:Acids; D000577:Amides; D010455:Peptides; D002725:Chloroform