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  • Title: 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.
    Author: Altmann E, Altmann KH, Nebel K, Mutter M.
    Journal: Int J Pept Protein Res; 1988 Nov; 32(5):344-51. PubMed ID: 3145251.
    Abstract:
    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.
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