Enantiomeric amine

Based on gasliquidchromatography (GLPC) amides, formed from various enantiomeric amines and the chiral-derivatizing reagent ( S)-(—)-JV-pentafluorobenzoylprolyl-l-imidazole, could be detected at nanogram levels [43],[44]... 

The ligands discussed so far all contained C2 symmetry. An important new class of ligands having Ci symmetry was introduced by Togni [22] (see Figure 4.19). They can be easily made from an enantiomeric amine as the precursor in a few steps. Different substituents can be introduced at the phosphorus atoms. In addition to the chiral carbon atom the molecule has planar chirality as well. The chiral carbon atom is used to introduce the planar chirality, i.e. lithiation of the ferrocenyl amine takes place at a specific side of the amine at the ferrocene moiety. 

Chromatographic separatum of enantiomersThe carbamate, ureido, and amide derivatives obtained without racemization from enantiomeric amines, alcohols, and carboxylic acids, respectively (equations T III), with this isocyanate are stable for months and are suitable for gas chromatographic separation using a polymeric chiral stationary phase (derived, for example, from L-valine-(S)-a-phenylethylamide). This methodology permits separation of chiral a- and /1-hydroxy acids and also N-mclhylnmino acids. 

Diastereomeric complexes can also be formed by ion-pairing of an enantiomer with a chiral counterion. In order to form this diastereomeric complex, it has been postulated that at least three interaction points between the ion pair are required [250]. Nearly all of these form weak complexes in aqueous mobile phases. Consequently, the chromatographic methods that have been developed have been either silica or diol columns with low-polarity mobile phases. Enantiomeric amines, such as the beta-blockers, have been optically resolved when (-l-)-lO-camphorsulfonic acid was used as the chiral counterion [251]. Enantiomers of norephedrine, ephedrine, pseudoephedrine, and phenyramidol have all been resolved from their respective enantiomers with n-dibutyltartrate [252]. Enantiomers of naproxen, a chiral carboxylic acid, are resolved from each other by either using quinidine or quinine in the mobile phase [253]. In these studies, silica... 

The noncovalent helicity induction and chiral memory concept is versatile enough to produce and maintain either a right- or left-handed helix because the helix-sense is predetermined by the chirality of the enantiomeric amines used. Consequently, the opposite enantiomeric helicity induction and the memory requires the opposite enantiomeric amine, followed by replacement with achiral amines. However, both mirror-image enantiomeric helices can be produced with a high efficiency from a helical poly(phenylacetylene) induced by a single enantiomer (Fig. 26) [129]. This dual memory of enantiomeric... 

The reagent tris[3-t-butylhydroxymethylene)-D-camphorato]Eu(III) was used initially to separate the resonances of R and S enantiomeric amines [53]. The fluorinated reagent tris[3-trifluoroacetyl-D-camphorato]Eu(III), Eu(facam)3 was used in the separation of resonances of enantiomers of 2-phenyl-2-butanol. The spectra of 2-phenyl-2-butanol on addition of Eu(thd)3 and Eu(facam)3 are shown in Fig. 10.21. As seen in the figure, Eu(thd)3 did not cause changes in the resonances while Eu(facam)3 caused separation of a-methyl resonances into two peaks, and resolved the -methyl triplets into a quintuplet and thus distinguishing the two isomers [54],... 

Derivatives of L-proline and 10-camphorsulfonic acid have been used to resolve enantiomeric amines through the formation of diastereoisomeric ion pairs. The concept of reciprocity in these separations. has been shown to occur in such a way that if the R enantiomer of acid HA resolves base B into its R- and 5-enantio-mers, an enantiomer of B (for example, R-B) can be used to resolve R-HA and 5-HA. 

These macrocyclic ethers assume a crown-like shape in solution with a central cavity capable of containing a small solute. They bind to small cationic species through association with the electron-rich oxygens of the ether linkage. Chiral crown ethers (Fig. 31) serve as selectors for enantiomeric amines in the protonated state. They have been used as mobile-phase... 

Pettersson, C Schill, G. Separation of enantiomeric amines by ion-pair chromatography. J. Chromatogr. 1981,204 (1), 179-183. 

In this model the sense of asymmetric induction is controlled by two principle factors (i) coordination of borane on the least-hindered face of the bicyclic ring system and (ii) coordination of the Lewis acid syn to the small group (R ). The latter point is in good agreement with the structural data that has been presented in this chapter, and is further supported by results from the asymmetric reduction of oxime ethers (Figure 51). As predicted by the model (75 and 78), (E) and (Z)-oxime ethers afford enantiomeric amines upon reduction by the reagent derived from (-)-norephedrine and borane (2 equiv.). Here, Lewis acid coordination is dictated by the ( )/(Z) stereochemistry of the oxime ether rather than by the rule of coordination syn to the small group. 

Karlsson, A., Pettersson, C. Separation of enantiomeric amines and acids using chiral ion-pair chromatography on porous graphitic carbon. Chirality, 1992, 4, 323-332. 

Precision preparative separation of enantiomeric amines by liquid chromatography of diastereomeric 4-hydroxybutyr-amides, Angew. Chem., 1979, 91, 66-68. 

Ion-pair formation with a chiral counterion has also been used to separate enantiomers. Thus, separation of enantiomeric amines has been achieved by ion-... 

Examination of the enantioselectivities in Table 7.5 indicates a striking difference in selectivity achieved in the reduction of cyclic (entries 1-8) vs. acyclic imines (entries 9-11). The former is very nearly 100% stereoselective. The simple reason for this is that the acyclic imines are mixtures of E and Z stereoisomers, which reduce to enantiomeric amines vide infra). The mechanism proposed for this reduction is shown in Scheme 7.11 [86]. The putative titanium(III) hydride catalyst is formed in situ by sequential treatment of the titanocene BINOL complex with butyllithium and phenylsilane. The latter reagent serves to stabilize the catalyst. Kinetic studies show that the reduction of cyclic imines is first order in hydrogen and first order in titanium but zero order in imine. This (and other evidence) is consistent with a fast 1,2-insertion followed by a slow hydrogenolysis (a-bond metathesis), as indicated [86]. Although P-hydride elimination of the titanium amide intermediate is possible, it appears to be slow relative to the hydrogenolysis. 

Two decades later, the methodology was significantly better for both these aspects. Therefore, Kirmse and Siegfried (1983) investigated the deamination of both enantiomeric amines again, not only in acetic acid, but also in water and in two carboxylic acids with large alkyl groups (3,3-dimethylbutyric acid and 2-ethylhexanoic acid), which are less polar than acetic acid. 

K) In the presence of a potent base, we may alkylate the lactam and then produce the tertiary amine by reduction with LiAlHit. The amine may now be resolved by employing optically active dibenzoyltartaric acid. After separation and regeneration, one of the enantiomeric amines coincides with a degradation product of morphine. 

Potential Separations of Enantiomeric Amines Using Silica Gel-Bound Chiral Macrocyclic Ligands... 

We will attach the chiral ligand which displays the best recognition for the enantiomers of the chiral organic amines to silica gel in a manner similar to that given in Scheme I. Although Cram and his coworkers have attached one chiral macrocycle to silica or polystyrene gel [34], few actual separations of chiral organic amines or ammonium salts have been carried out. We expect to demonstrate enantiomeric separations of specific enantiomeric amines. 

The interaction that creates diastereomers out of enantiomers need not be covalent. Weaker, non-covalent complexes are often discriminating enough to allow separation of enantiomers. The most classical way to separate enantiomeric amines is to form salts with a... 

FIGURE 6.39 Amine inversion interconverts enantiomeric amines. 

A facile synthesis of 2,3,5-tri-O-acetyl-p-D-ribofuranosyl isothiocyanate fiom the corresponding ribosyl chloride has been detailed. 2,3,4,6-Tetia-D-acetyl- 3-D-glucopyianosyl isothiocyanate continues to be a popular reagent for preparing diastereomeric thiourea or dithiocarbamate derivatives in the reversed-phase resolution of enantiomeric amine- or thiol-... 

SCHEME 16.69 The C(5)-bridged-mode, intermolecular-[4 + 2]/intiamolecular-[3 + 2] cycloaddition with the dienophile of E-configuration. Formation of enantiomeric amines 361a and 361b from the same starting materials but using different Lewis acids. 

Carlsson Y, Hedeland M, Bondesson U, Pettersson C. Nonaqueous capillary electrophoretic separation of enantiomeric amines with (—)-2,3 4,6-di-0-isopropylidene-2-keto-L-gulonic acid as chiral counter ion. J. Chromatogr. A 2001 922 303-311. 

Fluorescent dye. Reagent for the resolution of enantiomeric amines. Yellow powder. 

Reagent for the optical resolution of enantiomeric amines. R) form [113701-20-5]... 

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