Quininium Malates: Partial Chiral Discrimination via Diastereomeric Salt Formation

Quinine was employed as a resolving agent for racemic malic acid. The resultant product was a quininium salt containing 75 % of the D-malate anion. Quinine was also crystallized with pure L- and D-malic acids and the structures of the resulting diastereomeric salts were elucidated. The crystal packings were analyzed in terms of their non-bonded interactions and the conformation of the quinine, which was compared with other quinine structures recorded in the Cambridge Structural Database. The results indicate that the mechanism of enantiomeric resolution is reliant upon hydrogen bonded interactions.KEYWORDS: Chiral discrimination, diastereomeric salt, quinine

Chiral discrimination in the solid state

The methods of enantiomeric resolution have been studied extensively, and involve the process of spontaneous resolution by crystallisation, diastereomer formation, enzymatic transformations and chromatographic methods. However, to our knowledge, no detailed study of the correlation between structure in the solid state and enantiomeric resolution has been carried out. We have taken a different approach to the question of enantiomeric resolution in order to understand the mechanism of the molecular recognition that drives the differentiation of the resolving agent for one particular enantiomer. A series of supramolecular systems was analyzed to investigate the mechanism of chiral discrimination in the solid state. We have set up a series of competition experiments where the resolving agent was exposed to mixtures of enantiomers, and the mole fraction of the starting mixture were varied systematically. The ensuing solutions were allowed to crystallise and the mole fraction of the entrapped enantiomer were measured by analysing the crystal structure. This is an extension of the technique employed to measure the selectivity prole of a given host compound (H) towards a pair of guests A and B, whereby the host, H is dissolved in a series of solutions where the mole fraction XA varies in steps from 0 to 1. The resulting crystals are analysed, yielding mole fractions of XA as ZA. The selectivity coefcient at each point is then defined as and is a measure of the discrimination of the host for a given guest. In our case the two guests were replaced by (R)- and (S)-enantiomers. One obtains more information regarding the resolution process when the selectivity is relatively poor and the targeted (R)- and (S)-enantiomers are both entrapped in the same crystal, although in different proportions. In this manner, one can assess the forces that impinge on both guests as they are entrapped in the crystal structure and the resultant conformation changes that occur in the host in order to best accommodate these guests

One-dimensional Cd<SUP>II</SUP> coordination polymers: solid solutions with Ni<SUP>II</SUP>, thermal stabilities and structures

NatuurwetenskappeChemie & PolimeerwetenskapPlease help us populate SUNScholar with the post print version of this article. It can be e-mailed to: [email protected]

Salts of (+)-deoxycholic acid with amines : structure, thermal stability, kinetics of salt formation, decomposition and chiral resolution†

(+)-Deoxycholic acid forms salts with 1-propylamine, di-n-butylamine, sec-butylamine and 3-methyl-2- butylamine. The salts were characterised using thermal analysis and single crystal X-ray diffraction. The chiral discrimination of (+)-deoxycholic acid for racemic sec-butylamine and racemic 3-methyl-2- butylamine was studied and correlated with the structural and thermal results. A mixture of (+)- deoxycholic acid and racemic sec-butylamine yielded crystals of (R)-2-butylammonium deoxycholate. (+)- Deoxycholic acid was exposed to vapours of propylamine and racemic sec-butylamine and the kinetics of absorption were determined. The kinetics of decomposition of powdered samples obtained from (+)- deoxycholic acid with di-n-butylamine and racemic sec-butylamine were investigated. Crystallisation of (+)- deoxycholic acid with racemic 3-methyl-2-butylamine resulted in crystals of (S)-3-methyl-2-butylammo- nium deoxycholate

Resolution of (±)-citronellic acid with (–)-cinchonidine: The crystal struture of the cinchonidium-(S)-citronellate diastereomeric salt

A successful optical resolution of the racemic modification of citronellic acid was carried out by using (–)-cinchonidine, one of the cinchona alkaloids. The resultant crystals contain the protonated cinchonidinium cation and the (S)-(–)-itronellate anion in 1:1 ratio

Resolution of 1‚1´-binaphthyl-2‚2´-dicarboxylic acid with quinine: Structure of the intermediate (S)-1,1´-binaphthyl-2,2´-dicarboxylate dihydrate diastereomeric salt

Racemic 1,1′-binaphthyl-2,2′-dicarboxylic acid (BNDA) was resolved using quinine as the resolving agent. The structure of the resultant quininium (S)-1,1′-binaphthyl-2,2′-dicarboxylate dihydrate salt (1) was elucidated. The asymmetric unit contained one 1,1′-binaphthyl-2,2′-dicarboxylate anion, two quininium cations and two water molecules. The structure was solved successfully in the orthorhombic space group P212121 with unit cell dimensions: a = 11.100(2) Å, b = 16.572(3) Å, c = 28.726(6) Å.CPUT and the NRF (Pretoria) for funding

Inclusion of 1,4-bis(diphenylhydroxymethyl)benzene with amides: structure and selectivity

The host compound 1,4-bis(diphenylhydroxymethyl)benzene is shown to include a series of amides: N, N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), N-methylacetamide (NMA) and Nmethylformamide (NMF). The resultant inclusion compounds were characterised using thermal analysis and single crystal X-ray diffraction. A kinetic experiment was performed on the DMF clathrate and the activation energy determined. The host selectivity for the amides was studied through competition experiments.NRF (Pretoria) and the Cape Peninsula University of Technolog