Position of side-chain branching and handedness of turns and helices of homopeptides from chiral Cα-methylated amino acids. Crystal-state structural analysis of (αMe)Leu trimer and tetramer
| Autor: | Wilhelmus H. J. Boesten, Daniel Bayeul, André Aubry, Gilles Precigoux, Marco Crisma, Hans E. Schoemaker, Johan Kamphuis, Claudio Toniolo, Fernando Formaggio, M. Pantano |
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| Rok vydání: | 1994 |
| Předmět: | |
| Zdroj: | J. Chem. Soc., Perkin Trans. 2. :525-529 |
| ISSN: | 1364-5471 0300-9580 |
| DOI: | 10.1039/p29940000525 |
| Popis: | Terminally blocked homotri- and homotetra-peptides from (αMe)Leu, a chiral Cα-methylated, γ-branched α-amino acid, have been prepared by solution methods and fully characterized. The molecular and crystal structures of pBrBz-[D-(αMe)Leu]3-OH monohydrate and pBrBz-[D-(αMe)-Leu]4-OBut(where pBrBz indicates p-bromobenzoyl) were determined by X-ray diffraction. The tripeptide carboxylic acid adopts a type-III β-turn conformation followed by an uncommon oxyanalogue of a type-III β-turn, the latter being stabilized by a 1â†�4 CO ⋯ H–O intramolecular H-bond. The three independent molecules in the asymmetric unit of the tetrapeptide ester are folded in a regular right-handed 310-helix. All (αMe)Leu residues exhibit φ, Ψ torsion angles in the helical region of the conformational map. These results indicate that: (i) the (αMe)Leu residue is an effective β-turn and helix promoter and (ii) the relationship between (αMe)Leu chirality and turn and helix handedness is the same as that shown by the γ-branched (αMe)Phe residue, but it is opposite to that characteristic of isovaline (Iva), with a linear side chain, the β-branched (αMe)Val residue and protein amino acids (including Leu). |
| Databáze: | OpenAIRE |
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