Pietrzyński G, Rzeszotarska B, Ciszak E, Lisowski M, Kubica Z, Boussard G
Department of Organic Chemistry, University of Opole, Poland.
Int J Pept Protein Res. 1996 Oct;48(4):347-56.
The crystal structure and solution conformation of Ac-Pro-deltaAla-NHCH3 and the solution conformation of Ac-Pro-(E)-deltaAbu-NHCH3 were investigated by X-ray diffraction method and NMR, FTIR and CD spectroscopies. Ac-Pro-deltaAla-NHCH3 adopts an extended-coil conformation in the crystalline state, with all-trans peptide bonds and the deltaAla residue being in a C5 form, phi(1)=-71.4(4), psi(1)=-16.8(4), phi(2)= -178.4(3) and psi(2)= 172.4(3) degrees. In inert solvents the peptide also assumes the C5 conformation, but a gamma-turn on the Pro residue cannot be ruled out. In these solvents Ac-Pro-(E)-deltaAbu-NHCH3 accommodates a beta(II)-turn, but a minor conformer with a nearly planar disposition of the CO-NH and C=C bonds (phi(2) approximately 0 degrees) is also present. Previous spectroscopic studies of the (Z)-substituted dehydropeptides Ac-Pro-(Z)-deltaAbu-NHCH3 and Ac-Pro-deltaVal-NHCH3 reveal that both peptides prefer a beta(II)-turn in solution. Comparison of conformations in the family of four Ac-Pro-deltaXaa-NHCH3 peptides let us formulate the following order of their tendency to adopt a beta-turn in solution: (Z)-deltaAbu > (E)-deltaAbu > deltaVal; deltaAla does not. None of the folded structures formed by the four compounds is stable in strongly solvating media.
通过X射线衍射法以及核磁共振、傅里叶变换红外光谱和圆二色光谱对Ac-Pro-δAla-NHCH3的晶体结构和溶液构象以及Ac-Pro-(E)-δAbu-NHCH3的溶液构象进行了研究。Ac-Pro-δAla-NHCH3在晶体状态下呈伸展螺旋构象，所有肽键均为反式，δAla残基呈C5形式，φ(1)=-71.4(4)，ψ(1)=-16.8(4)，φ(2)= -178.4(3)，ψ(2)= 172.4(3)度。在惰性溶剂中，该肽也呈C5构象，但不能排除Pro残基上存在γ-转角。在这些溶剂中，Ac-Pro-(E)-δAbu-NHCH3包含一个β(II)-转角，但也存在一个次要构象体，其CO-NH和C=C键几乎呈平面排列(φ(2)约为0度)。先前对(Z)-取代脱氢肽Ac-Pro-(Z)-δAbu-NHCH3和Ac-Pro-δVal-NHCH3的光谱研究表明，这两种肽在溶液中都倾向于形成β(II)-转角。对四种Ac-Pro-δXaa-NHCH3肽家族构象的比较使我们能够确定它们在溶液中形成β-转角倾向的以下顺序：(Z)-δAbu > (E)-δAbu > δVal；δAla则不然。这四种化合物形成 folded structures在强溶剂化介质中均不稳定。
