Crystal structure and conformation of a cyclic tetrapeptide cyclo(L-Pro-Sar)2 containing all-cis peptide units
✍ Scribed by Katsuhiko Ueno; Toshimi Shimizu
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1983
- Tongue
- English
- Weight
- 419 KB
- Volume
- 22
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Abstract
The crystal structure and conformation of the synthetic cyclic tetrapeptide, cyclo(L‐Pro‐Sar)~2~, was determined by x‐ray analysis. The peptide crystallizes in the orthorhombic space group __P__2~1~2~1~2~1~ with cell parameters a = 9.277(1), b = 12.884(1), and c = 15.581(2) Å. The crystal structure was solved by the symbolic addition procedure for direct phase determination and least‐squares refinement using 1796 reflections, which led to the final R value of 0.043. This structure provides the first example observed in a crystal of a cyclic tetrapeptide in which all four peptide units have been found in the cis conformation with ω angles deviating slightly by 2°–10° from the ideal value of 0°. It was also found that the two Pro C^α^‐CO single bonds assumed a trans′ (ψ = 159.6° and 158.4°) conformation. Adjoining average planes of the peptide groups fall at nearly right angles to each other. The pyrrolidine ring conformations of the two prolyl residues are in the envelope form, with C^γ^ carbon out of the least‐squares planes for the remaining four atoms.