Oligopeptide (FK)4 facilitates the determination of the absolute stereochemistry of chiral organic compounds via NMR Spectroscopy

Abstract

Molecular chirality plays a crucial role in the fields of chemistry and biology. Various nuclear magnetic resonance (NMR) methods have been employed for assignment of stereochemical configurations. Alignment media for measurements of anisotropic parameters contribute to configuration elucidations, while chiral auxiliaries assist in enantiomer discrimination and chiral recognition. However, each method comes with limitations, and the assignment of absolute configuration by NMR remains challenging. In this study, we explored a combined approach for absolute configuration elucidation with the multifaceted application of the oligopeptide (FK)4, which possesses dual functionalities as an alignment medium for anisotropic NMR measurements and a chiral differentiating agent. As an alignment medium, (FK)4 facilitates the analysis of stereochemical features through residual dipolar couplings (RDC), aiding in the structural elucidation of stereoisomers. Moreover, (FK)4 exhibits unique chiral differentiating properties, interacting distinctly with enantiomers and resulting in observable bifurcation of chemical shift signals, in 13C, 1H and 19F spectra. Using isoleucine and xylose as model compounds, we demonstrate how the dual functionality of (FK)4 enables the identification of stereoisomeric structures via RDC parameters and the assignment of enantiomeric configurations through measurements of t2 relaxation time coupled with theoretical simulations. These findings highlight the potential of versatile chiral media as (FK)4 for approaching the elucidation of absolute configurations of organic molecules via combined NMR spectroscopy approaches, with implications for structural characterization and enantiomer discrimination in chemical applications.