title: Conformation and chiral effects in α,β,α-tripeptides.
abstract: Short α,β,α-tripeptides comprising a central chiral trisubstituted β(2,2,3)*-amino acid residue form unusual γ-turns and δ-turns in CDCl(3) and DMSO-d(6) solutions but do not form β-turns. Thermal coefficients of backbone amide protons, 2D-NMR spectra, and molecular modeling revealed that these motifs were strongly dependent on the configuration (chiral effect) of the central β-amino acid residue within the triad. Accordingly, SSS tripeptides adopted an intraresidual γ-turn like (C6) arrangement in the central β-amino acid, whereas SRS diastereomers preferred an extended δ-turn (C9) conformation. A different SRS-stabilizing bias was observed in the crystal structures of the same compounds, which shared the extended δ-turn (C9) found in solution, but incorporated an additional extended β-turn (C11) to form an overlapped double turn motif.
authors: Instituto de Productos Naturales y Agrobiología del CSIC, Avda. Astrofísico Francisco Sánchez 3, 38206 La Laguna, Tenerife, Spain.
authors: Carlos J
authors: CJ
authors: Saavedra
authors: Alicia
authors: A
authors: Boto
authors: Rosendo
authors: R
authors: Hernández
authors: José Ignacio
authors: JI
authors: Miranda
authors: Jesus M
authors: JM
authors: Aizpurua
mesh_terms: D002236:Carbohydrate Conformation; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D009842:Oligopeptides