Conformational studies on host-guest peptides containing chiral alpha-methyl-alpha-amino acids. Comparison of the helix-inducing potential of alpha-aminoisobutyric acid, (S)-2-ethylalanine and (S)-2-methylserine.
The conformational behaviour of host-guest peptides of the type Ac-Ala-Xxx-Ala-Ala-Xxx-Ala-Ala-Xxx-Ala-Ala-NH-PEGM (Xxx = alpha-aminoisobutyric acid (Aib), (S)-2-ethylalanine ((S)-Iva), (S)-2-methylserine ((S)-alpha-MeSer)) has been studied by CD spectroscopy in CF3CH2OH, CH3OH, and water and by i.r. spectroscopy in CHCl3 and in the solid state. In this way the relative helix-inducing potential of the two chiral alpha-methyl-alpha-amino acids (S)-Iva and (S)-alpha-MeSer could be established in comparison to the strong helix-former Aib. The results show that (S)-Iva exerts a comparable helix-inducing effect as Aib, making this amino acid a valuable complementary tool for the stabilization or induction of helices. No significant helix-promoting effect was observed for (S)-alpha-MeSer in polar solvents; however, the i.r.-spectroscopic data in CHCl3 and in the solid state point to a helical conformation under these conditions. Possible reasons for the different behaviour of (S)-Iva and (S)-alpha-MeSer are briefly discussed.
Altmann
E
E
Institute of Organic Chemistry, University of Basel, Switzerland.
Altmann
K H
KH
Nebel
K
K
Mutter
M
M
D000621:Aminoisobutyric Acids; D002725:Chloroform; D002942:Circular Dichroism; D007536:Isomerism; D000432:Methanol; D010455:Peptides; D011487:Protein Conformation; D012694:Serine / Q000031:analogs & derivatives*; D012997:Solvents; D013055:Spectrophotometry, Infrared; D014270:Trifluoroethanol; D014633:Valine; D014867:Water
D000621:Aminoisobutyric Acids; D010455:Peptides; D012997:Solvents; D014867:Water; C100049:2-aminoisobutyric acid; C035563:2-methylserine; D012694:Serine; C032737:isovaline; D014270:Trifluoroethanol; D002725:Chloroform; D014633:Valine; D000432:Methanol