α,β‐Dehydro amino acid residues are known to constrain the peptide backbone to the β‐bend conformation. A pentapeptide containing only one α,β dehydrophenylalanine (ΔPhe) residue has been synthesized and crystallized, and its solid state conformation has been determined. The pentapeptide Boc‐Leu‐Phe‐Ala‐ΔPhe‐Leu‐OMe (C39H55N5O8, Mw = 721.9) was crystallized from aqueous methanol. Monoclinic space group was P21, a = 10.290(2)°, b = 17.149(2)°, c = 12.179(2) Å, β = 96.64(1)° with two molecules in the unit cell. The x‐ray (Mo Kα, λ = 0.7107A) intensity data were collected using a CAD4 diffractometer. The crystal structure was determined by direct methods and refined using least‐squares technique. R = 4.4% and Rw = 5.4% for 4403 reflections having |F0| ≥ 3σ(|F0|). All the peptide links are trans and the pentapeptide molecule assumes 310‐helical conformation. The mean ϕ,ψ values, averaged over the first four residues, are −64.4°, −22.4° respectively. There are three 4 → 1 intramolecular hydrogen bonds, characteristic of 310,‐helix. In the crystal, the peptide helices interact through two head‐to‐tail. NHO intermolecular hydrogen bonds. The peptide molecules related by 21, screw symmetry form a skewed assembly of helices. © 1995 John Wiley & Sons, Inc.
All Science Journal Classification (ASJC) codes
- Organic Chemistry