Conformational investigation of α, β-dehydropeptides |
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Authors: | EWA CISZAK,GRZEGORZ PIETRZY
SKI,BARBARA RZESZOTARSKA |
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Affiliation: | EWA CISZAK,GRZEGORZ PIETRZYÑSKI,BARBARA RZESZOTARSKA |
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Abstract: | The crystal structure of Ac-Pro-ΔVal-NHCH3 was examined to determine the influence of the α,β-dehydrovaline residue on the nature of peptide conformation. The peptide crystallizes from methanol-diethyl ether solution at 4° in needle-shaped form in orthorhombic space group P212121 with a= 11.384(2) Å, b = 13.277(2) Å, c = 9.942(1) Å. V = 1502.7(4) Å3 Z = 4, Dm= 1.17 g cm?3 and Dc=1.18 g cm?3 The structure was solved by direct methods using SHELXS-86 and refined to an R value of 0.057 for 1922 observed reflections. The peptide is found to adopt a β-bend between the type I and the type III conformation with φ1=?68.3(4)°, ψ1=? 20.1(4)°, φ2=?73.5(4)°= and Ψ2=?14.1(4)°=. An intramolecular hydrogen bond between the carbonyl oxygen of ith residue and the NH of (i+ 3)th residue stabilizes the β-bend. An additional intermolecular N.,.O hydrogen bond joins molecules into infinite chains. In the literature described crystal structures of peptides having a single α,β-dehydroamino acid residue in the (i+ 2) position and forming a β-bend reveal a type II conformation. |
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Keywords: | acctyl-l-prolyl-α β -dehydrovalinc methylamide: β -bend crystal structure: α ,β -dehydroamino acid residue α ,β -dehydropeptide conformation α ,β -dehydrovaline peptide conformation X-ray studies |
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