In tube determination of the absolute configuration of alpha- and beta-hydroxy acids by NMR via chiral BINOL borates

Azaheterocyclic diphenylmethanol chiral solvating agents for the NMR chiral discrimination of alpha-substituted carboxylic acids

A series of small-membered heterocycle probes, so-called azaheterocycle-containing diphenylmethanol chiral solvating agents (CSAs), have been developed for NMR enantiodiscrimination. These chiral sensors were readily synthesized were inexpensive and efficiently used for the chiral analysis of alpha-substituted carboxylic acids. The sensing method was operationally simple and the processing was straightforward. Notably, we propose (S)-aziridinyl diphenylmethanol as a promising CSA, which has excellent chiral discriminating properties and offers multiple detectable possibilities pertaining to the 1H NMR signals of diagnostic split protons (including 25 examples, up to 0.194 ppm, 77.6 Hz). Its ability to detect the molecular recognition of fluorinated carboxylic acids were further investigated, with a good level of discrimination via the 19F NMR spectroscopic analysis. In addition, an accurate enantiomeric excess (ee) analysis of the p-methoxyl-mandelic acid with different optical compositions have been calculated based on the integration of well-separated proton signals.

Efficient Enantiodifferentiation of Carboxylic Acids Using BINOL-Based Amino Alcohol as a Chiral NMR Solvating Agent

A new optically active BINOL-amino alcohol has been designed and synthesized in a good yield and applied as chiral nuclear magnetic resonance (NMR) solvating agent for enantioselective recognition. Analysis by ¹H NMR spectroscopy demonstrated that it has excellent enantiodifferentiation properties toward carboxylic acids and non-steroidal anti-inflammatory drugs (14 examples). The non-equivalent chemical shifts (up to 0.641 ppm) of various mandelic acids were evaluated by the reliable peak of well-resolved ¹H NMR signals. In addition, enantiomeric excesses of the ortho-chloro-mandelic acid with different enantiomeric ratio were calculated based on integration of proton well-separated splitting signals.

A chiral sensor for recognition of varied amines based on 19F NMR signals of newly designed rhodium complexes

A novel chiral octahedral rhodium complex containing fluorine has been developed to be an excellent chiral sensor for a variety of amines including diamines, monoamines, amino alcohols and amino acids, showing well distinguishable 19F NMR signals and an accurate measurement of enantiomeric determination.

Assigning the Absolute Configurations of Chiral Primary Amines Based on Experimental and DFT-Calculated 19F Nuclear Magnetic Resonance

In this work, a novel method for assigning the absolute configuration of a chiral primary amine has been developed based on the experimental and DFT-calculated 19F NMR chemical shift differences of its derived two fluorinated amides by reacting with two enantiomers of a chiral derivatizing agent FPP (α-fluorinated phenylacetic phenylselenoester) separately. Comparing the experimental chemical shift difference Δ δ α - F R , S of (R)-FPA-amide/(S)-FPA-amide with the calculated Δδα-F R,S of (R)-FPA-(R)-amide/(S)-FPA-(R)-amide, if the experimental Δδα-F R,S has the same symbol (positive or negative) as one of the theoretical Δδα-F R,S , the assigned configuration of the amine is considered to be consistent with the theoretical one. Our method could be applied to a broad substrate scope avoiding wrong conclusion due to empirical judgment.

A chiral aluminum solvating agent (CASA) for 1H NMR chiral analysis of alcohols at low temperature

A chiral aluminum solvating agent (CASA) was demonstrated to be a general and efficient reagent for ¹H NMR chiral analysis of alcohols.

The assignment of the configuration for α-hydroxy acid esters using a CEC strategy

A simple and efficient (1)H NMR method for determining the absolute configuration of chiral α-hydroxy acid esters using a competing enantioselective conversion (CEC) strategy was developed. The α-hydroxy acid esters were acylated in the presence of Feng's chiral N,N'-dioxide-scandium(iii) complex, and the faster reaction was identified when one enantiomer of the chiral α-hydroxy acid ester was treated with both enantiomers of the ligand by NMR analysis of the reaction mixture without further purification. A mnemonic is presented to aid the assignment of the absolute configuration of the substrates.

p-TsOH promotes 2′-amino-[1,1′-binaphthalene]-2-ol as a chiral solvating agent

Ternary complex of p-TsOH, NOBIN with hydroxy acids and their derivatives permit NMR spectroscopic chiral discrimination.

Efficient Determination of the Enantiomeric Purity and Absolute Configuration of Flavanones by Using (S)-3,3'-Dibromo-1,1'-bi-2-naphthol as a Chiral Solvating Agent

The enantiomeric purity and absolute configuration of flavanones were first determined using (S)-3,3'-dibromo-1,1'-bi-2-naphthol as a chiral solvating agent by means of (1)H NMR spectroscopy. The enantiomeric purity results closely matched those based on chiral HPLC analysis.

A simple and rapid approach for testing enantiopurity of hydroxy acids and their derivatives using 1H NMR spectroscopy

A rapid and the simple chiral derivatizing protocol involving the coupling of 2-formylphenylboronic acid and an optically pure [1,1-binaphthalene]-2,2-diamine is introduced for the accurate determination of the enantiopurity of hydroxy acids and their derivatives.

Chirality sensing of amines, diamines, amino acids, amino alcohols, and α-hydroxy acids with a single probe

A stereodynamic probe for determination of the absolute configuration and enantiomeric composition of chiral amines, diamines, amino alcohols, amino acids, and α-hydroxy carboxylic acids is described. The chirality sensing is based on spontaneous asymmetric transformation of the first kind with stereolabile binaphtholate boron and zinc complexes. The substrate binding and chiral amplification processes yield a distinctive chiroptical sensor output at high wavelength that can be used for rapid and accurate ee detection of minute sample amounts.

Facile determination of the absolute configurations of α-hydroxy acids by chiral derivatization coupled with liquid chromatography-mass spectrometry analysis

α-Hydroxy acids are commonly encountered in natural bioactive molecules. For convenient determination of the absolute configurations of α-hydroxy acids, a simple method, named the "O-Marfey method" was developed using a chiral derivatization strategy with (L-fluoro-2,4-dinitrophenyl-5)-L-alanine amide (L-FDAA). The liquid chromatography-mass spectrometry (LC-MS) analysis of the derivatives clearly determined the absolute configurations of various α-hydroxy acids based on their elution times and sequences. This new method is operationally simple with short reaction time and sensitive enough for application at a sub-milligram scale without any purification. This method also enables the simultaneous chirality analysis of α-hydroxy acids and α-amino acids. The absolute configuration of a natural depsipeptide bearing an α-hydroxy acid and α-amino acids was successfully determined by our O-Marfey application.

Aminoindanol-based chiral derivatizing agents for the determination of the absolute configuration of carboxylic acids

New chiral derivatizing agents have been prepared through a simple, short-step synthesis. The absolute configuration of α-chiral carboxylic acids can be assigned on the basis of the NMR chemical shift difference between diastereomeric esters. Because of the modular structures of the agents, the anisotropic effect could be easily manipulated to afford large chemical shift differences even in polar solvents.

Peptidolipins B-F, antibacterial lipopeptides from an ascidian-derived Nocardia sp

A marine Nocardia sp. isolated from the ascidian Trididemnum orbiculatum was found to produce five new lipopeptides, peptidolipins B-F (1-5), which show distinct similarities to the previously reported L-Val(6) analog of peptidolipin NA. Synthetic modification of peptidolipin E (4) was used to determine the location of an olefin within the lipid chain. The advanced Marfey's method was used to determine the absolute configurations of the amino acids. Peptidolipins B (1) and E (4) demonstrated moderate antibacterial activity against methicillin-resistant Staphylococcus aureus and methicillin-sensitive Staphylococcus aureus.

New chiral derivatizing agents: convenient determination of absolute configurations of free amino acids by 1H NMR

The chiral carbonate reagents 5 allow for the direct and unambiguous determination of the absolute configurations of a wide range of free amino acids using (1)H NMR. By using a approximately 3:1 mixture of (S)-5 and (R)-5, absolute configurations of the corresponding carbamates are determined by only analyzing the nitrogen protons.