Mining Chromatographic Enantioseparation Data Using Matched Molecular Pair Analysis.

We apply matched molecular pair (MMP) analysis to data from ChirBase, which contains literature reports of chromatographic enantioseparations. For the 19 chiral stationary phases we examined, we were able to identify 289 sets of pairs where there is a statistically significant and consistent difference in enantioseparation due to a small chemical change. In many cases these changes highlight enantioselectivity differences between pairs or small families of closely related molecules that have for many years been used to probe the mechanisms of chromatographic chiral recognition; for example, the comparison of N-H vs.

Strong enantioselective self-recognition of a small chiral molecule.

In the present report, we have crystallized a single enantiomer and the racemate of N-3,5-dinitrobenzoyl (DNB) leucine. In both cases, the X-ray structures show clear evidence of homochiral dimerization in the solid state. Moreover, only homochiral dimers were observed in the unit cell of the racemate, a result of solid-state enantioselective complexation.

Formation of stable Meisenheimer adduct ion pairs in apolar solvents: implications for stereoselective reactions.

[reaction: see text] A detailed study concerning the formation of Meisenheimer adducts in biphasic solvent systems is described. The process relies on utilizing a significantly lipophilic quaternary ammonium salt to transfer a nucleophile (e.g.

The effects of aromatic substituents on the chromatographic enantioseparation of diarylmethyl esters with the whelk-O1 chiral stationary phase.

Members of a series of diarylmethanols, diarylmethyl pivalates, and diarylmethyl acetates (analyte sets 1-26) were enantioresolved with the (S,S)-Whelk-O1 chiral stationary phase (CSP). An analogue of the (S,S)-Whelk-O1 selector was combined with enantioenriched samples of the various diarylmethyl pivalates and thereby used as a chiral solvating agent (CSA) for high field 1H NMR studies. The absolute configurations of a number of chiral diarylmethyl pivalates were assigned using this approach, and hydrolysis of the pivalates allowed assignment of the absolute configurations of the corresponding diarylmethanols.

Enantioresolution of fluorinated diphenylmethanols and determination of their absolute configurations by X-Ray crystallographic and 1H NMR anisotropy methods.

Various fluorinated diphenylmethanols were enantioresolved by the methods of chiral camphorsultam-dichlorophthalic acid (CSDP acid) and/or 2-methoxy-2-(1-naphthyl)propionic acid (MalphaNP acid) yielding enantiopure alcohols. Their absolute configurations were unambiguously determined by X-ray crystallography of CSDP esters and/or by the (1)H NMR anisotropy method of MalphaNP esters for the first time.

Enantioresolution and absolute configurations of chiral meta-substituted diphenylmethanols as determined by X-ray crystallographic and 1H NMR anisotropy methods.

meta-Substituted diphenylmethanols were enantioresolved by the method of chiral phthalic acid yielding enantiopure alcohols. Their absolute configurations were unambiguously determined by X-ray crystallography of chiral phthalate esters and/or by the (1)H NMR anisotropy method using 2-methoxy-2-(1-naphthyl)propionic acid.

Enantioselective hydrolysis of N-acylated alpha-amino esters at a biphasic interface: tandem reaction kinetic resolution using a chiral complexing agent.

[reaction: see text] Highly enantioselective hydrolytic kinetic resolutions of esters derived from N-acylated alpha-amino acids proceed rapidly at hydrocarbon/water interfaces in the presence of a proline-derived chiral selector. When performed in tandem with an enantioselective biphasic esterification reaction, esters of 100% enantiomeric excess are obtained

Comparison of CD spectra of (2-methylphenyl)- and (2,6-dimethylphenyl)-phenylmethanols leads to erroneous absolute configurations.

Enantiopure (2,6-dimethylphenyl)phenylmethanol (+)-(3) and analog (+)-(4) were prepared and their CD spectra were found opposite to that of (2-methylphenyl)phenylmethanol (R)-(-)-(2), the absolute configuration of which was previously established by X-ray crystallography. Therefore the S absolute configuration was once assigned to (+)-3 and (+)-4. After that we have succeeded in the X-ray analyses of chiral dichlorophthalate esters of (+)-3 and (+)4, which clearly indicated R absolute configuration.

X-ray Crystallographic Evidence in Support of a Proposed Chiral Recognition Mechanism.

A new family of pi-basic chiral selectors has been developed and employed in the separation of enantiomers by liquid chromatography. These chiral selectors, derived from (S)-proline and designed from mechanistic considerations, show high levels of discrimination between the enantiomers of N-(3,5-dinitrobenzoyl)amino acid esters and amides. A considerable amount of chromatographic data has been assembled, all of it consistent with the proposed chiral recognition mechanism.

Intermolecular (1)H-(1)H Two-Dimensional Nuclear Overhauser Enhancements in the Characterization of a Rationally Designed Chiral Recognition System.

Chiral stationary phases (CSPs) for liquid chromatography derived from N-(acyl)proline-3,5-dimethylanilides separate the enantiomers of N-(3,5-dinitrobenzoyl)-alpha-amino esters and amides with high levels of selectivity. These CSPs have been used to assemble a large body of chromatographic data which indirectly supports the validity of the mechanistic rationale originally used in the design of these CSPs. We herein report (1)H and (13)C chemical shift data obtained when the (S)-enantiomer of chiral solvating agent (CSA) 3, a soluble analogue of the selector used in CSP (S)-1, acts on each of the enantiomers of the dimethylamide of N-(3,5-dinitrobenzoyl)leucine, 2.