Crystal Structure and NMR of an α,δ‐Peptide Foldamer Helix Shows Side‐Chains are Well Placed for Bifunctional Catalysis: Application as a Minimalist Aldolase Mimic**
摘要:
摘要 我们首次报告了由异构 1 .1 序列的 α- 和 δ- 氨基酸形成的不寻常的 13/11 螺旋(交替的 i, i+1 {NH-O=C} 和 i, i+3 {C=O-H-N} H 键)的核磁共振和 X 射线衍射 (XRD) 结构,并展示了这种框架在催化方面的应用:1 序列的 α- 和 δ- 氨基酸,并展示了这一框架在催化方面的应用。虽然分子内氢键(IMHB)是该系统中螺旋形成的明显驱动力,但我们还观察到序列中一个δ-氨基酸的乙基残基与下一个δ-残基的环己基之间的极性相互作用,这种相互作用似乎使一种螺旋比另一种螺旋更稳定。据我们所知,这种导致特定螺旋偏好的额外稳定作用以前从未观察到过。重要的是,所实现的螺旋类型将 α-残基的功能性置于足够近的位置,以进行双功能催化,这在我们的系统作为最小化醛缩酶模拟物的应用中得到了证明。
Stereospecific Synthesis of Conformationally Constrained γ-Amino Acids: New Foldamer Building Blocks That Support Helical Secondary Structure
作者:Li Guo、Yonggui Chi、Aaron M. Almeida、Ilia A. Guzei、Brian K. Parker、Samuel H. Gellman
DOI:10.1021/ja907233q
日期:2009.11.11
A highly stereoselective synthesis of novel cyclically constrained gamma-amino acid residues is presented. The key step involves organocatalytic Michael addition of an aldehyde to 1-nitrocyclohexene. After aldehyde reduction, this approach provides optically active beta-substituted delta-nitro alcohols (96-99% ee), which can be converted to gamma-amino acid residues with a variety of substituents at
The invention provides compounds and methods, for example, to carry out organocatalytic Michael additions of aldehydes to cyclically constrained nitroethylene compounds catalyzed by a proline derivative to provide cyclically constrained α-substituted-γ-nitro-aldehydes. The reaction can be rendered enantioselective when a chiral pyrrolidine catalyst is used, allowing for Michael adducts in nearly optically pure form (e.g., 96 to >99% e.e.).
The Michael adducts can bear a single substituent or dual substituents adjacent to the carbonyl. The Michael adducts can be efficiently converted to cyclically constrained protected γ-amino acid residues, which are essential for systematic conformational studies of γ-peptide foldamers. New methods are also provided to prepare other γ-amino acids and peptides. These new building blocks can be used to prepare foldamers, such as α/γ-peptide foldamers, that adopt specific helical conformations in solution and in the solid state.