Linear and cyclic β3-oligopeptides with functionalised side-chains (-CH2OBn, -CO2Bn, -CH2CH2CO2Bn) derived from serine and from aspartic and glutamic acid
作者:Jennifer L. Matthews、Karl Gademann、Bernhard Jaun、Dieter Seebach
DOI:10.1039/a805478i
日期:——
The natural β-amino acid derivative Boc-Asp(β-OH)-OBn, as well as Boc-β-HGlu(OBn)-OH and Boc-β-HSer(OBn)-OH (prepared from appropriately protected glutamic acid and serine, respectively, by ArndtâEistert homologation), were employed as building blocks for the synthesis of linear (11â20) and cyclic (21â23) β-oligopeptides consisting of two to six β-amino acids [using trichloroethyl (TCE) ester groups for C-terminal protection and pentafluorophenyl-ester activation for macrocyclisation]. While the linear derivatives are soluble enough for reactions and structural investigations in solution, the cyclo-β-tri- and -hexapeptides are not (according to FT-IR measurements they form networks of hydrogen bonds, perhaps consisting of so-called nanotubes). The CD spectra of the BocâOTCE-protected (19) and of the unprotected (20) β-hexapeptides [β-Asp(OBn)-β-HGlu(OBn)-β-HSer(OBn)]2 differ drastically, and only the unprotected form shows the familiar pattern of a negative Cotton effect between 210 and 220 nm (indicative of a 314 helix). An NMR analysis in methanol of the β-hexapeptide 20 with free termini reveals the presence of a single, central, left-handed helix turn (14-membered hydrogen-bonded ring). The results are discussed and compared with those obtained previously for analogous β-peptides carrying non-functionalised side chains.
天然的β-氨基酸衍生物Boc-Asp(β-OH)-OBn,以及Boc-β-HGlu(OBn)-OH和Boc-β-HSer(OBn)-OH(分别通过Arndt-Eistert同系化法从适当保护的谷氨酸和丝氨酸制备),被用作合成由2到6个β-氨基酸组成的线性(11-20)和环状(21-23)β-寡肽的构建模块[使用三氯乙基(TCE)酯基团进行C端保护和五氟苯酯激活进行大环化]。尽管线性衍生物在溶液中足以用于反应和结构研究,但环状β-三肽和六肽则不然(根据FT-IR测量,它们形成了氢键网络,可能是由所谓的纳米管组成)。Boc-OTCE保护的六肽(19)和无保护的六肽(20)[β-Asp(OBn)-β-HGlu(OBn)-β-HSer(OBn)]2的CD光谱存在显著差异,只有无保护形式在210到220 nm之间显示熟悉的负Cotton效应模式(表明为314螺旋)。在甲醇中对自由末端的六肽20进行NMR分析揭示了存在一个中心、左旋的螺旋转弯(14元氢键环)。结果进行了讨论并与先前获得的具有非功能化侧链的类似β-肽的结果进行了比较。