Synthesis and conformational analysis of 18-membered Aib-containing cyclohexapeptides
作者:Tatjana Jeremic、Anthony Linden、Kerstin Moehle、Heinz Heimgartner
DOI:10.1016/j.tet.2004.12.012
日期:2005.2
Solid-state conformational analysis of 1 and 2 was performed by X-ray crystallography and has revealed some unusual features as all three Aib residues of 1 assume nonhelical conformations. Furthermore, the residue Aib4 adopts an extended conformation (ϕ=−175.9(3)°, ψ=+178.6(2)°), which is, to the best of our knowledge, the first observation of an Aib residue adopting an extended conformation in a cyclopeptide
描述了两个含有Aib的环状六肽,环(Gly-Aib-Leu-Aib-Phe-Aib)2和环(Leu-Aib-Phe-Gly-Aib-Aib)2的合成和构象分析。使用溶液相技术制备1和2的线性前体,并检测三种不同偶联剂(HATU,PyAOP,DEPC)的环化效率。发现环化的成功与试剂有关。通过X射线晶体学对1和2进行固态构象分析,结果发现了一些不寻常的特征,因为1的三个Aib残基假定为非螺旋构象。此外,残基Aib 4具有扩展构象(ϕ = −175.9(3)°,ψ = + 178.6(2)°),据我们所知,这是对Aib残基采用扩展构象的首次观察环肽中的构象。1的结构也是一个罕见的例子,其中Aib残基占据通过分叉氢键稳定的II'型β-转角的(i +1)位置。环状肽2在固态上具有更规则的构象,其由两个I / I'型稠合的β-转角组成,并通过一对分子内氢键稳定。此外,DMSO-中环肽1的构象研究d