Residual‐Chemical‐Shift‐Anisotropy‐Based Enantiodifferentiation in Lyotropic Liquid Crystalline Phases Based on Helically Chiral Polyacetylenes

Abstract

Anisotropic NMR spectroscopy, revealing residual dipolar couplings (RDCs) and residual chemical shift anisotropies (RCSAs) has emerged as a powerful tool to determine the configurations of synthetic and complex natural compounds. The deduction of the absolute in addition to the relative configuration is one of the primary goals in the field. Therefore, the investigation of the enantiodiscriminating capabilities of chiral alignment media becomes essential. While RDCs and RCSAs are used for the determination of the relative configuration now routinely, RCSAs have not been measured in chiral alignment media such as chiral liquid crystals. Herein, we present this application by measuring RCSAs for chiral analytes such as indanol and isopinocampheol in the lyotropic liquid crystalline phase of an L‐valine derived helically chiral polyacetylenes. We have also demonstrated that a single 1D 13C‐{1H} NMR spectrum suffices to get the RCSAs circumventing the necessity to acquire two spectra at two alignment conditions.

Polyarylisocyanides Derived from an Alkyne-Pd(II) Catalyst as Robust Alignment Media with Excellent Enantiodiscimination

“…Next, we embarked on evaluating the enantiodiscriminating properties of poly- 1 by measuring the RDC data of several chiral compounds. Previous pioneering studies on other chiral media utilized the enantiomeric isopinocampheol (IPC) as test analytes. − IPC 3 is particularly suitable due to its high rigidity and minimal overlap in CLean InPhase (CLIP)-HSQC spectra . We were able to extract up to 11 natural abundance proton-carbon one-bond RDCs ( 1 D CH ) for both (+)- and (−)-IPC in M -poly- l - 1 and P -poly- d - 1 LLCs, respectively, at 298 K in CD 2 Cl 2 .…”

“…Various chiral alignment media have been developed for this purpose, including gelatin, polysaccharides, homopolypeptides, and helical polymers. − In addition to the originally proposed chiral polypeptide-based homopolymers by Courtieu et al, which include the representative poly-γ-benzyl- l -glutamate (PBLG), , an increasing number of other polypeptides with modified side-chains, such as PPLA, PBLA, PSMBLG, etc. and their enantiomeric forms, have been developed in the Thiele lab. − Notably, Reggelin et al have demonstrated that polyacetylenes serve as excellent lyotropic liquid crystal (LLC) phases as weak alignment media, exhibiting pronounced enantiodifferentiating capabilities in CDCl 3 . − Meanwhile, ongoing research by the same group has revealed that polyarylisocyanides exhibit moderate enantiodifferentiating capabilities for ketones and alcohols, but less pronounced effects for amines and other molecules . In our previous work, we investigated the self-assembled oligopeptides named OPAs, which only showed weak enantiodifferentiating capabilities. , We also explored the use of helical polymer polyisocyanopeptides (PIP) as an alignment medium.…”

Tandem “One-Shot” Measurement of Residual Chemical Shift Anisotropy and Residual Dipolar Coupling using Biphasic Supramolecular Peptide Liquid Crystals

“…In this regard, the isotropic chemical shift changes could be isolated, but experimental errors might be introduced due to the instrument status and experimental conditions. To circumvent the necessity of repeatedly acquiring spectra under two experimental conditions, recently, biphasic LC media based on poly-γ-benzyl-L -glutamate (PBLG) 19 and L-valine-derived polyphenylacetylene (PLA) 20 have been developed to realize the "one-shot" measurement of RCSAs, which showed the merits of a faster analysis, self-referencing, less material, and high accuracy. Notably, the RCSA data have been acquired mainly in CDCl 3 -bearing systems.…”