A Bifunctional Phenylalanine–Lysine Oligopeptide Enabling Both Chiral Differentiation and Relative Configuration Analysis by Nuclear Magnetic Resonance Spectroscopy

Bifunctional agents that integrate solvent alignment and chiral differentiation could streamline NMR-based structural and stereochemical analysis. Yet alignment media that simultaneously induce enantiodifferentiation remain rare, particularly in protic solvents and across chemically diverse molecules. In this study, we demonstrate that the amphiphilic oligopeptide (FK)₄ self-assembles into β-sheet fibrils that serve as such a bifunctional medium. Upon assembly, (FK)₄ weakly aligns the solvent environment while providing sufficient intermolecular interactions for robust enantiomeric differentiation. (FK)₄ supports the enantiodifferentiation of diverse chiral compounds (amino acids, carbohydrates, organic acids, and pharmaceuticals) across multiple nuclei (¹H, ¹³C, and ¹⁹F), yielding well-resolved resonance bifurcations for accurate enantiopurity quantification through integration. The bifunction of (FK)₄ extends to water and protic organic solvents, allowing both residual chemical shift anisotropies (RCSAs) measurements and enantiodifferentiation in the same sample. This dual functionality enables a streamlined postsynthesis analysis workflow for simultaneous determination of enantiomeric composition and relative configuration in racemic reaction products. Integrating structural elucidation and chiral analysis, (FK)₄ offers a perspective on extending anisotropic NMR techniques to stereochemical differentiation with the potential to facilitate absolute configuration elucidation.