Models for chiral recognition in molecular complexation

Helgeson, Roger C.; Timko, Joseph M.; Moreau, P.; Peacock, Stephen C.; Mayer, James M.; Cram, Donald J.

doi:10.1021/ja00828a039

Cited by 113 publications

(32 citation statements)

References 4 publications

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“…8 Crown ethers, the most common of which have an 18-crown-6 unit, are primarily known for their ability to form host-guest complexes with and distinguish chiral primary amines. [9][10] The primary amine is analyzed as its protonated ammonium ion. The NH þ 3 unit forms three hydrogen bonds to oxygen atoms of the 18-crown-6 unit as shown in Figure 1a.…”

Section: Introductionmentioning

confidence: 99%

Chiral NMR discrimination of amines: Analysis of secondary, tertiary, and prochiral amines using (18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid

Lovely

Wenzel

2007

Chirality

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Enantiomeric discrimination is observed in the 1H and 13C NMR spectra of secondary and tertiary amines in the presence of (-)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (1). Nonequivalence of the resonances of prochiral nuclei in primary and secondary amines is also observed when they associate with 1. The amines are added in their neutral form and are protonated by the carboxylic acid groups of 1 to produce the corresponding ammonium and carboxylate ions. Secondary amines associate with 1 through two hydrogen bonds and an ion pair interaction. Tertiary amines can only form one hydrogen bond to accompany the ion pairing. Chiral discrimination in the 1H and 13C NMR spectra of a series of aryl-containing secondary amines is of sufficient magnitude to determine enantiomeric purities. The discrimination in the spectra of tertiary amines with 1 is smaller, but 13C NMR spectra provided enough distinction for the determination of enantiomeric purity.

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Section: Introductionmentioning

confidence: 99%

Chiral NMR discrimination of amines: Analysis of secondary, tertiary, and prochiral amines using (18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid

Lovely

Wenzel

2007

Chirality

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“…NMR spectroscopy showed rapid host/guest association/dissociation rates at levels appropriate for efficient LC. 48 The chiral host was bonded to a styrenic-resin 49 or to a silica-gel support 50 through a ''leash'' attached to a naphthyl moiety, and used as a chiral bonded phase to separate racemic amines and amino acid esters, as their ammonium salts, under normal phase LC conditions. Another host of the 6-crown ether was prepared that contained a single bi-naphthyl moiety that was substituted in its 3,3Ј-positions with two -CH 2 OCH 2 CO 2 H ''arms.''…”

Section: Cram's Crown Ethersmentioning

confidence: 99%

Chiral separation of enantiomers via selector/selectand hydrogen bondings

Feibush¹

1998

Chirality

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“…This will cause different time-averaged solvation environments that may contribute to chiral recognition in the NMR spectrum. Chiral crown ethers have been an important group of host compounds for the enantiodiscrimination of protonated primary amines [6,7,8,9,10,11]. More recently, a chiral crown ether with a larger cavity was used for the chiral discrimination of secondary amines [12].…”

Section: Introductionmentioning

confidence: 99%

Chiral recognition in NMR spectroscopy using crown ethers and their ytterbium(III) complexes

Wenzel

Freeman

Sęk

et al. 2004

Analytical and Bioanalytical Chemistry

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Chiral crown ethers 1 and 5 are useful enantiomeric discriminating agents in 1H NMR spectroscopy for neutral and protonated primary amines, amino acids, and amino alcohols. The presence of the carboxylic acid groups in 1 and 5 provide sites at which ytterbium(III) can bind. Adding ytterbium(III) nitrate to crown-substrate mixtures in methanol-d4 causes shifts in the spectra of substrates and often enhances the chiral discrimination in the 1H NMR spectrum. The enhancement in enantiomeric discrimination that occurs in the presence of ytterbium(III) allows lower concentrations of the crown ether to be used in chiral recognition studies. Several amide derivatives of 1 were prepared and evaluated as chiral NMR discriminating agents, although except for 1e, these were less effective than 1.

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Models for chiral recognition in molecular complexation

Cited by 113 publications

References 4 publications

Chiral NMR discrimination of amines: Analysis of secondary, tertiary, and prochiral amines using (18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid

Chiral NMR discrimination of amines: Analysis of secondary, tertiary, and prochiral amines using (18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid

Chiral separation of enantiomers via selector/selectand hydrogen bondings

Chiral recognition in NMR spectroscopy using crown ethers and their ytterbium(III) complexes

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