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Chiral discrimination of dicarboxylic acids with Cinchona alkaloids
Author(s)
Komba, Christele Lydia
Date Issued
2017
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
This thesis is aimed at the investigation of the chiral discrimination process during diastereomeric salt
formation, when selected cinchona alkaloids are exposed to racemic mixtures of tartaric acid
derivatives. This research is based on the use of (+)‐cinchonine, (‐)‐cinchonidine, (‐)‐quinidine and (+)‐
quinine, which served as chiral bases, in order to resolve racemates of O,O'‐dibenzoyl‐tartaric acid
(DBTA) and O,O'‐di‐p‐toluoyl‐tartaric acid (DTTA). Cinchona alkaloids were selected because of their
abilities to form salts with the targeted acids. DBTA and DTTA are commonly used resolving agents to
separate racemic bases via diastereomeric salt formation, and they are also commercially available and
affordable chiral acids. Results were obtained from all combination but only the experiments with
cinchonidine were included in this thesis, namely [CIND+][L‐DBTA‐], 2[CIND+][D‐DBTA2‐], [CIND+][LDTTA‐]
and 2[CIND+][D‐DTTA2‐]∙2DMSO∙0.7H2O. Experimental analytical techniques, such as thermal
analysis, powder X‐ray diffraction, and single crystal X‐ray diffraction were used to analyze the
harvested diastereomeric salts. A correlation of molecular parameters derived from the structures and
an investigation of the mechanism, which drives the resolution process were discussed.
The thesis also summarizes the findings on 8 inclusion compounds of (‒)‐O,O'‐dibenzoyl‐(2R,3R)‐tartaric
acid (L‐DBTA) and (‒)‐O,O'‐di‐p‐toluoyl‐(2R,3R)‐tartaric acid (L‐DTTA) or their racemic mixtures, (rac)‐
DBTA and (rac)‐DTTA, with DMSO and water: (rac)‐DBTA∙H2O, (rac)‐DBTA∙DMSO, L‐DBTA∙H2O, LDBTA∙
DMSO, (rac)‐DTTA∙H2O, (rac)‐DTTA∙DMSO, L‐DTTA∙H2O, and L‐DTTA∙DMSO. The discussed
inclusion compounds were obtained serendipitously, as a product of the pre‐screening of suitable
solvents to dissolve both the acids and the cinchona alkaloids during the discrimination experiments.
Only few crystal structures of solvates of these two tartaric acid derivatives are known up to now, and
fewer of these structures do exist when both the racemic and the enantiopure acid encapsulates the
same solvent. The synthesis and structural analysis of these inclusion compounds contribute to the pool
of available crystal structures when comparing chiral vs. achiral crystal forms of the same compounds.
formation, when selected cinchona alkaloids are exposed to racemic mixtures of tartaric acid
derivatives. This research is based on the use of (+)‐cinchonine, (‐)‐cinchonidine, (‐)‐quinidine and (+)‐
quinine, which served as chiral bases, in order to resolve racemates of O,O'‐dibenzoyl‐tartaric acid
(DBTA) and O,O'‐di‐p‐toluoyl‐tartaric acid (DTTA). Cinchona alkaloids were selected because of their
abilities to form salts with the targeted acids. DBTA and DTTA are commonly used resolving agents to
separate racemic bases via diastereomeric salt formation, and they are also commercially available and
affordable chiral acids. Results were obtained from all combination but only the experiments with
cinchonidine were included in this thesis, namely [CIND+][L‐DBTA‐], 2[CIND+][D‐DBTA2‐], [CIND+][LDTTA‐]
and 2[CIND+][D‐DTTA2‐]∙2DMSO∙0.7H2O. Experimental analytical techniques, such as thermal
analysis, powder X‐ray diffraction, and single crystal X‐ray diffraction were used to analyze the
harvested diastereomeric salts. A correlation of molecular parameters derived from the structures and
an investigation of the mechanism, which drives the resolution process were discussed.
The thesis also summarizes the findings on 8 inclusion compounds of (‒)‐O,O'‐dibenzoyl‐(2R,3R)‐tartaric
acid (L‐DBTA) and (‒)‐O,O'‐di‐p‐toluoyl‐(2R,3R)‐tartaric acid (L‐DTTA) or their racemic mixtures, (rac)‐
DBTA and (rac)‐DTTA, with DMSO and water: (rac)‐DBTA∙H2O, (rac)‐DBTA∙DMSO, L‐DBTA∙H2O, LDBTA∙
DMSO, (rac)‐DTTA∙H2O, (rac)‐DTTA∙DMSO, L‐DTTA∙H2O, and L‐DTTA∙DMSO. The discussed
inclusion compounds were obtained serendipitously, as a product of the pre‐screening of suitable
solvents to dissolve both the acids and the cinchona alkaloids during the discrimination experiments.
Only few crystal structures of solvates of these two tartaric acid derivatives are known up to now, and
fewer of these structures do exist when both the racemic and the enantiopure acid encapsulates the
same solvent. The synthesis and structural analysis of these inclusion compounds contribute to the pool
of available crystal structures when comparing chiral vs. achiral crystal forms of the same compounds.
Additional information
Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2017
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