Comparison of the effect of five guest residues on the β-sheet conformation of host (L-val)n oligopeptides

Abstract

The synthesis, characterization, and IR absorption, ¹H NMR, and CD properties of (L-Val)_n, host tetra-, penta-, and hexapeptides containing an L-Ile, L-Ala, D-ValL, L-Pro, or Aib guest residue are reported, with the intention of establishing a scale of 0-sheet disrupting capability of various amino acids. The results indicate that in the solid state the 0-sheet structures of the (D-Val)(, n = 5,6) homopeptides are at least partially disrupted by the L-Pro and Aib residues. In CH₂C1₂/Me₂S0so lvent mixtures the following rank order is obtained for the stability of the P-sheets: L-Val > L-Val > L-Ile » L-Ala »c D-Vd > L-Pro » Aib. In CDC1₃ solutions the Aib hexapeptide is folded into a partially labile 3₁₀-helicals tructure. Statistically disordered conformations largely prevail in more polar solvents like 2,2,2-trifluoroethanol and ethanol in all the peptides examined. Only the (L-Val), hexapeptide is prone to adopt the β-sheet on formation upon addition of 40% (v/v) water to the trifluoroethanol solution.