Conformational investigation of alpha,beta-dehydropeptides. VII. Conformation of Ac-Pro-deltaAla-NHCH3 and Ac-Pro-(E)-deltaAbu-NHCH3: comparison with (Z)-substituted alpha,beta-dehydropeptides.

G Pietrzyński, B Rzeszotarska, E Ciszak, M Lisowski, Z Kubica, G Boussard
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Abstract

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.

脱氢肽的构象研究。7Ac-Pro- deltaala - nhch3和Ac-Pro-(E)- deltaabu - nhch3的构象:与(Z)取代的-脱氢肽的比较。
采用x射线衍射、核磁共振、红外光谱和CD光谱研究了Ac-Pro- deltaala - nhch3和Ac-Pro-(E)- deltaabu - nhch3的晶体结构和溶液构象。Ac-Pro-deltaAla-NHCH3在结晶状态下为延伸线圈构象,全反式肽键和deltaAla残基呈C5形式,phi(1)=-71.4(4), psi(1)=-16.8(4), phi(2)= -178.4(3), psi(2)= 172.4(3)度。在惰性溶剂中,肽也呈C5构象,但不能排除在Pro残基上的γ -turn。在这些溶剂中,Ac-Pro-(E)- deltaabu - nhch3可容纳β (II)-旋,但co - nhh和C=C键几乎呈平面分布(φ(2)约为0度)的次要构象也存在。先前对(Z)取代的脱氢肽Ac-Pro-(Z)- deltaabu - nhch3和Ac-Pro- deltaaval - nhch3的光谱研究表明,这两种肽在溶液中都倾向于β (II)-转变。通过比较四个ac - pro - deltaaa - nhch3肽族的构象,我们可以得出它们在溶液中倾向于β -旋向的顺序:(Z)-deltaAbu > (E)-deltaAbu > deltaal;deltaAla没有。这四种化合物形成的折叠结构在强溶剂化介质中都不稳定。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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