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Because choice of chiral nuclear magnetic resonance (NMR) shift reagents and concentration conditions have been made empirically by trials and errors for chiral NMR analyses, the prediction of NMR signal separation behavior is an urgent issue. In this study, the separation of enantiomeric and enantiotopic 1H and 13C NMR signals for α‐amino acids and tartaric acid was performed by using the praseodymium(III) complex with (S,S)‐ethylenediamine‐N,N′‐disuccinate ((S,S)‐EDDS). All the present D‐amino acids exhibited larger downfield shift of their α‐protons and α‐carbons compared with those for the corresponding L‐amino acids in common. This regularity is applicable to absolute configurational assignment and determination of optical purity of amino acids. The chemical shifts of β‐protons of d‐ and l‐alanine fully bound with the Pr(III) ((S,S)‐EDDS) complex (δbs) and the adduct formation constants of both enantiomers (Ks) were obtained by dependences of the observed downfield shifts of the β‐protons on the total concentrations of the respective enantiomers in the presence of a constant concentration of the Pr(III) complex. The difference in the K values was found to be predominant determining factor for the enantiomeric signal separation. The chemical shifts of both enantiomers (δs) and the enantiomeric signal separations (Δδs) under given conditions could be calculated from the δb and K values. Furthermore, prediction of the signal separation behavior was enabled by using the calculated δ values and the signal broadening obtained by dependences of the half‐height widths of the observed signals on the bound/free substrate concentration ratios for the respective enantiomers. [ABSTRACT FROM AUTHOR]

Enantiomeric 1H and 13C NMR signal separation behaviors of various α-amino acids and DL-tartarate were investigated by using the samarium(III) and neodymium(III) complexes with ( S, S)-ethylenediamine- N, N'-disuccinate as chiral shift reagents. A relatively smaller concentration ratio of the lanthanide(III) complex to substrates was suitable for the neodymium(III) complex compared with the samarium(III) one, striking a balance between relatively greater signal separation and broadening. To clarify the difference in the signal separation behavior, the chemical shifts of β-protons for fully bound D- and L-alanine (δb(D) and δb(L)) and their adduct formation constants ( Ks) were obtained for both metal complexes. Preference for D-alanine was similarly observed for both complexes, while it was revealed that the difference between the δb(D) and δb(L) values is the significant factor to determine the enantiomeric signal separation. The neodymium(III) and samarium(III) complexes can be used complementarily for higher and smaller concentration ranges of substrates, respectively, because the neodymium(III) complex gives the larger difference between the δb(D) and δb(L) values with greater signal broadening compared to the samarium(III) complex. [ABSTRACT FROM AUTHOR]

Phosphoric acid derivatives containing chiral Betti base fragment were synthesized by reacting racemic and enantiopure N-Boc-protected 1-(α-aminobenzyl)-2-naphthols with diethyl chlorophosphate followed by deprotection. [ABSTRACT FROM AUTHOR]

• The effect of Eu(hfc) 3 on the hydrogen signal chemical shift of a series of bi-1,2,3-triazoles was studied by 1H NMR. • A signal discrimination in 1H NMR spectra was found, indicating the formation of atropisomers in these molecules. • The rotational barriers around the C5−C5' bond for bi-1,2,3-triazoles were calculated using the DFT (B3LYP) method. • Significant energy barriers (up 34 kcal/mol) a low atropisomer interconversion were found in bi-1,2,3-triazoles. The effect of europium tris 3-(heptafluoropropylhydroxymethylene)-(+)-camphorate on the hydrogen signal chemical shift of a series of bi-1,2,3-triazoles was studied by 1H NMR, displaying a signal discrimination which indicates the formation of atropisomers in these molecules. In addition, the rotational barrier around the C5−C5' bond for bi-1,2,3-triazoles was calculated using the DFT (B3LYP) method with 6-31G** basis set, revealing significant energy barriers (up 34 kcal/mol) at 204–206° dihedral angles and a low atropisomer interconversion. These elements allow a direct method for recognition of chiral bi-1,2,3-triazoles derived from copper-catalyzed azide-alkyne cycloaddition. [Display omitted] [ABSTRACT FROM AUTHOR]

Readily available L-tartaric acid, which is a bidentate ligand with two chiral centers forming a seven-membered chelate ring, was applied to the chiral ligand for the chiral (NMR) shift reagent of samarium(III) formed in situ. This simple method does not cause serious signal broadening in the high magnetic field. Enantiomeric 13C and 1H NMR signals and enantiotopic 1H NMR signals of α-amino acids were successfully resolved at pH 8.0 and the 1:3 molar ratio of Sm(NO3)3:L-tartaric acid. It is elucidated that the enantiomeric signal resolution is attributed to the anisotropic magnetic environment for the enantiomers induced by the chiral L-tartarato samarium(III) complex rather than differences in stability of the diastereomeric substrate adducts. The present 13C NMR signal resolution was also effective for the practical simultaneous analysis of plural kinds of DL-amino acids. Chirality 27:353-357, 2015.© 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: The 1,3-dipolar cycloaddition of adamantylidenefulvene (1) with 2equiv of nitrile oxides 2a–d gave 1/1 cycloadducts, 3a–d and 4a–d, as the major products, and four other 1/2 minor cycloadducts 5–8a,b. The ratios of 1/1 cycloadducts 3a–d to 4a–d in THF solution were about 1/1 in the four different nitrile oxides 2a–d studied and microwave was found to accelerate the reactions and enhance their yields. It is noteworthy that the regioselectivity of 3a/4a was enhanced to 71/29 in β-cyclodextrin (β-CD) aqueous solution compared to that of 40/60 in the absence of β-CD. The regioselectivity of 3b/4b was further enhanced to 99/1 when 4-tert-butylphenyl hydroximinoyl chloride (9b) was complexed with β-CD and then proceeded to react with 1; this is in sharp contrast with that of 33/67 in the absence of β-CD. The binding constant of 1·β-CD in acetone-d 6/D2O (1/1) was determined to be 188±9M−1 by 1H NMR titration experiments. The binding mode of 1·β-CD was further determined by ROESY experiment. Furthermore, molecular dynamic simulations were carried out to provide information of the complexation modes of 1·β-CD, 3a·β-CD, 4a·β-CD, 9a·β-CD, and 9b·β-CD. It was found that both steric and electrostatic effects play important roles in determining the regio- and stereochemistry of 1,3-dipolar cycloaddition of 1. Finally, β-CD is shown to serve as a chiral shift reagent to differentiate the enantiomers of 4a in 1H NMR. [Copyright &y& Elsevier]

The use of microorganisms or isolated enzymes in synthetic routes has been extensively used by industry and academic research. A great advantage of biotransformation in a synthetic route is highly regio- and enatiosselective control, which can be achieved through microbial catalyzed reaction. Biotransformation is one of the most efficient methods in a production of high purity optical compounds and development of efficient routes for target molecules. Biotransformation by Mucor ramosissimus of enedione 1 gave the keto-alcohol (-)-2 with enantiomeric excess (ee)>99,9% (determined by 1H NMR with [(+)-Eu(hfc)]3) and their epimer (-)-3. Determination of the absolute configuration of epimer (-)-3 was accomplished by controlled reaction and measuring of optical rotation (scheme 1). The fungus M. ramosissimus is a promising species to perform desymmetrization of diketones with high enantioselectivity.

Abstract: Experimental conditions for determination of enantiomeric composition of 1-substituted 3-aminocarboranes by 1H and 13C NMR spectroscopy using chiral shift reagent Eu(hfc)3 have been found. [Copyright &y& Elsevier]

An abstract of the article "Studies on the Diels-Alder adduct from cyclopentadiene and p-benzoquinone: Biotransformation, enantiomeric excess and absolute configuration" by Felipe Camargo Braga and colleagues is presented.