Conformational investigation of α,β-dehydropeptides |
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Authors: | MAREK LISOWSKI GRZEGORZ PIETRZYSKI BARBARA RZESZOTARSKA |
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Institution: | MAREK LISOWSKI,GRZEGORZ PIETRZY?SKI,BARBARA RZESZOTARSKA |
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Abstract: | Conformations of three series of model peptides: homochiral Ac-Pro-L-Xaa-NHCH3 and heterochiral Ac-Pro-D-Xaa-NHCH3 (Xaa=Phe, Val, Leu. Abu. Ala) as ivell as α,β-dehydro Ac-Pro-ΔXaa-NHCHs ΔXaa = (Z)-ΔPhe, ΔVal. (Z)-ΔLeu, (Z)-ΔAbu] were investigated by CD spectroscopy in 2 % dichloromethanecyclohexane, trifluoroethanol. water. and occasionally in other solvents. The spectra of homochiral peptides show a significant solvent dependence. Folded structures are present in 2% dichloromethane-cyclohexane and unordered ones occur in water. The folded conformers are of the inverse γ-turn type for all the peptides but Ac-Pro-L-Phe-NHCH3 for which the type-I β-turn is preferred. The changes in the spectra of the heterochiral peptides are limited. The compounds adopt the typc-II β–turn in 2% dichloromethanecyclohexane, represented by class B spectra, and retain this conformation in water as well as in fluorinated alcohols but not always to a full extent. The CD spectra of the unsaturated peptides in 2%, dichloromethanecyclohexane, although they cannot be assigned to any common spectral class, must be attributed to the βII-turn conformation as determined for these coinpounds by NMR and IR spectroscopy. The CD spectra of dehydropeptides exhibit a considerable solvent dependence and suggest unordered structures in water. |
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Keywords: | α β -dehydroamino acid residues α β -dehydropeptidc conformation β -turn circular dichroism conformational studies γ -turn phenylalaninc pepride CD proline peptides |
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