Peptide Hairpins with Strand Segments Containing α- and β- Amino Acid Residues : Cross – Strand Aromatic Interactions of Facing Phe Residues.

摘要: The incporation of \beta -amino acid residues into the strand segments designed -hairpin leads to formation polar sheets, since in case -peptide strands, all adjacent carbonyl groups point one direction and amide orient opposite direction. conformational analysis two peptide hairpins composed \alpha /\beta -hybrid are described: Boc-Leu-\beta Phe-Val-D-Leu-\beta -OMe (1) Boc-\beta Leu-Phe-\beta Val-DPro-Gly-\beta Val-OMe (2). A 500-MHz 1H-NMR (nuclear magnetic resonance) methanol supports a signi.cant population hairpin conformations both peptides. Diagnostic nuclear Overhauser effects (NOEs) observed cases. X-ray diffraction studies on single crystals 1 reveal conformation molecules, which constitute crystallographic asymmetric unit. Three cross-strand hydrogen bonds nucleating type II0 -turn at D-Pro-Gly segment independent molecules. In 1, Phe positions 2 7 occur nonhydrogen-bonding position, with benzyl side chains pointing faces -sheet. aromatic centroid-to-centroid distances 8.92A (molecule A) 8.94A B). 2, rings must occupy facing antiparallel NMR-derived structure.