Rondinini Virginia, Aiello Federica, Cefalì Federica, Recchimurzo Alessandra, Uccello Barretta Gloria, Balzano Federica
Department of Chemistry and Industrial Chemistry, University of Pisa, Via G. Moruzzi 13, 56124 Pisa, Italy.
National Research Council-Institute for Chemical and Physical Processes (CNR-IPCF), Via G. Moruzzi 1, 56124 Pisa, Italy.
Molecules. 2025 Jul 11;30(14):2930. doi: 10.3390/molecules30142930.
The bis-thiourea chiral solvating agent (CSA) enables the NMR-based determination of absolute configuration in -3,5-dinitrobenzoyl (DNB) amino acid derivatives without requiring covalent derivatization. A reliable trend of the sense of nonequivalence and absolute configuration is found in both H and C NMR spectra. A dual-enantiomer approach, using (,)- and (,)-, generates diastereomeric complexes with the enantiopure substrate, and distinct spatial arrangements are reflected in consistent and interpretable Δδ values. The observed chemical shift differences correlate reliably with the stereochemistry of the chiral center and are further supported by ROESY (Rotating-frame Overhauser Enhancement SpectroscopY) experiments and binding constants' measurements, confirming the formation of stereoselective non-covalent complexes. This methodology extends the logic of Mosher's analysis to solvating agents and remains effective even in samples containing single pure enantiomers of the amino acid derivative. The -based dual-CSA system thus represents a robust, non-derivatizing strategy for stereochemical assignment by NMR, combining operational simplicity with broad applicability to DNB derivatives of amino acids with free carboxyl function.
双硫脲手性溶剂化剂（CSA）能够在无需共价衍生化的情况下，基于核磁共振（NMR）测定3,5-二硝基苯甲酰基（DNB）氨基酸衍生物的绝对构型。在氢谱（H NMR）和碳谱（C NMR）中均发现了不等价性和绝对构型方向的可靠趋势。采用（+，+）-和（-，-）-双对映体方法，与对映体纯的底物生成非对映体复合物，不同的空间排列反映在一致且可解释的Δδ值中。观察到的化学位移差异与手性中心的立体化学可靠相关，并通过旋转框架奥弗豪泽效应光谱（ROESY）实验和结合常数测量得到进一步支持，证实了立体选择性非共价复合物的形成。该方法将莫舍尔分析的逻辑扩展到了溶剂化剂，甚至在含有氨基酸衍生物单一纯对映体的样品中也依然有效。因此，基于双CSA的系统代表了一种用于通过核磁共振进行立体化学归属的强大的非衍生化策略，兼具操作简便性以及对具有游离羧基功能的氨基酸的DNB衍生物的广泛适用性。
