Using NMR spectroscopic methods to determine enantiomeric purity and assign absolute stereochemistry

Synthesis and NMR Characterization of (Z,Z,Z,Z,E,E,ω)-Heptaprenol

“…Of these reagents, Eu(hcf) 3 was best. The use of chiral shifts to disperse the resonances of terpenoids for the purpose of structure assignment 31, 32 or for enantiomeric ratio determination 33–36 is known, but is infrequent. Optimization of the molar ratio of Eu(hcf) 3 to 4 for the purpose of structure assignment is shown in Figure 3.…”

Application of selective F1 decoupled 1H NMR for enantiomer resolution and accurate measurement of enantiomeric excess at low chiral substrate/auxiliary concentration

“…On the other hand, CSAs have a wide range of functionality and facilitate the discrimination of enantiomers in chiral molecules such as acids, alcohols, amides, aromatics, esters, lactams, lactones, sulfoxides, etc. There are several mechanisms possible for enantiomeric discrimination [9]. Usually (D)-enantiomer and (L)-enantiomer of the substrate form complexes with CSA with the respective association constants of K L and K D for the following equilibria L þ CSA K L L À CSA In most of the cases, these equilibria are in fast exchange on the NMR timescale and yield a population-weighted average of the complexed and free enantiomer signals to result in distinct signals for the enantiomers [1,24].…”

“…Enantiomers interact differently with an auxiliary to produce different diastereomeric complexes and consequently there is a difference in chemical shifts between the enantiomeric resonances. Very recently a review with a collection of more than four hundred references has been published which reports the recent advances in the development of chiral derivatizing and solvating agents that facilitate the determination of enantiomeric excess [9]. In the recent past, the chiral liquid crystal NMR techniques have undergone rapid development for the study of a wide range of chiral molecules [10][11][12].…”

Biotransformations of 2-hydroxy-2-(ethoxyphenylphosphinyl)acetic acid and the determination of the absolute configuration of all isomers

“…The first of the two most popular methods is to create a derivative with a chiral derivatizing agent (CDA), by creating a covalent bond and the introduction of an additional stereogenic center [3]. The second method is based on an analysis using chiral solvating agents (CSA), which form complexes with the analysed compound by weak interactions (e.g., hydrogen bonds, Van der Waals forces) [4]. Chiral hydroxyphosphonates are important precursors for the synthesis of a variety of important organophosphates [5][6][7].…”

“…However, due to their structure they are of great interest because they can find potential use as chiral auxiliaries in NMR methods for the determination of the enantiomeric purity and absolute configuration of various classes of compounds (data not yet published). Chiral auxiliaries may only be used if they are pure enantiomers [4]. Therefore, it is important to find a way to obtain these compounds in enantiomerically pure form.…”