Synthesis and binding properties of a macrobicyclic receptor for N-protected peptides with a carboxylic acid terminus
作者:Peter D. Henley、Christopher P. Waymark、Iain Gillies、Jeremy D. Kilburn
DOI:10.1039/a908090b
日期:——
A novel macrobicyclic receptor, 3, has been synthesised by linking together a diaminopyridine with suitable amino acids, followed by a double intramolecular cyclisation of a suitably activated precursor. Macrobicycle 3 features a diamidopyridine unit, designed to serve as a specific binding site for carboxylic acid functionality, at the base of an open, bowl-shaped cavity. Incorporation of additional amide functionality around the rim of the bowl-shaped structure provides further hydrogen bonding sites to interact with peptidic guests. The binding properties of 3 with N-protected amino acid and peptide derivatives have been investigated by NMR titration experiments, which reveal that 3 is a strong and selective receptor for peptides with a carboxylic acid terminus in CDCl3 solution, the strongest binding being observed with Cbz-β-alanyl-D-alanine (−ΔGass = 22.8 kJ mol−1). The macrobicycle is reasonably enantioselective (Cbz-β-alanyl-L-alanine, −ΔGass = 19.1 kJ mol−1) and notably the binding of Cbz-β-alanyl lactic acids is considerably weaker than the binding of the corresponding Cbz-β-alanyl alanines (ΔΔGass ≈ 8–9 kJ mol−1). Molecular modelling and 2D NMR studies have been carried out on the free macrobicycle and the 1:1 complex formed with the most strongly bound substrate (Cbz-β-alanyl-D-alanine). These studies provide a consistent picture of the macrobicycle as a flexible receptor, which is able to bind the Cbz-β-alanyl-D-alanine substrate in the macrobicyclic cavity with a series of well defined hydrogen bonds to the alanylalanine amide, and less well defined hydrogen bonds to the benzylcarbamate functionality.
通过将二氨基吡啶与适当的氨基酸连接在一起,然后对适当活化的前体进行双分子内环化,合成了一种新型大环受体 3。大循环 3 的特点是在一个开放的碗状空腔的底部设计了一个二氨基吡啶单元,作为羧酸功能的特定结合位点。在碗形结构的边缘还加入了额外的酰胺官能团,为与肽客体相互作用提供了更多的氢键位点。核磁共振滴定实验研究了 3 与 N 保护氨基酸和肽衍生物的结合特性,结果表明 3 在 CDCl3 溶液中对具有羧酸末端的肽具有很强的选择性受体,与 Cbz-β-alanyl-D-alanine 的结合最强(-ΔGass = 22.8 kJ mol-1)。大循环具有合理的对映选择性(Cbz-β-丙氨酰-L-丙氨酸,-ΔGass = 19.1 kJ mol-1),而且 Cbz-β-丙氨酰乳酸的结合力明显弱于相应的 Cbz-β-丙氨酰丙氨酸的结合力(ΔΔGass ≈ 8-9 kJ mol-1)。我们对游离大环和与结合力最强的底物(Cbz-β-丙氨酰-D-丙氨酸)形成的 1:1 复合物进行了分子建模和二维核磁共振研究。这些研究一致表明,大环自行车是一种灵活的受体,它能够通过一系列明确的氢键与丙氨酰丙氨酸酰胺结合,并通过不太明确的氢键与氨基甲酸苄酯官能团结合,从而将 Cbz-β- 丙氨酰-D-丙氨酸底物结合到大环自行车的空腔中。