New Resolution Technologies Controlled by Chiral Discrimination Mechanisms

Chiral co-selector induced chirality switching in the enantioseparation of ofloxacin by forming a co-crystal

The chiral selectivity in the cocrystal process could be switched by changing the combination of chiral co-selectors.

Helical alignment inversion of microtubules in accordance with a structural change in their lattice

Giant helical (oriented chiral nematic) alignments of microtubules of nanometer to centimeter lengths are known to form over a temperature gradient during anisotropic spiral propagation via tubulin dimer addition in a capillary cell. Such helical alignments may be modified by the addition of either paclitaxel or dimethyl sulfoxide, which induces a lattice (helical) structural change in the microtubule itself. In this study, we found that the lattice structural change of microtubules brings about inversion of microtubule alignments in the helical ordering. Based on microscopy and scattering data, a mechanism for the helical ordering of microtubules is discussed in relation to their lattice (helical) structure.

Resolution of 2-chloromandelic acid with (R)-(+)-N-benzyl-1-phenylethylamine: chiral discrimination mechanism

During the resolution of 2-chloromandelic acid with (R)-(+)-N-benzyl-1-phenylethylamine, the crystals of the less soluble salt were grown, and their structure were determined and presented. The chiral discrimination mechanism was investigated by examining the weak intermolecular interactions (such as hydrogen bond, CH/π, and van der Waals interactions) and molecular packing mode in crystal structure of the less soluble diastereomeric salt. A one-dimensional double-chain hydrogen-bonding network and a "lock-and-key" supramolecular packing mode are disclosed. The investigation demonstrates that hydrophobic layers with corrugated surfaces can fit into the grooves of one another to realize a compact packing, when the molecular structure of resolving agent is much larger than that of the racemate. This "lock-and-key" assembly is recognized to be another characteristic of molecular packing contributing to the chiral discrimination, in addition to the well-known sandwich-like packing by hydrophobic layers with planar boundary surfaces.

Partial resolution of racemictrans-4-[5-(4-alkoxyphenyl)-2,5-dimethylpyrrolidine-1-oxyl-2-yl]benzoic acids by the diastereomer method with (R)- or (S)-1-phenylethylamine

The partial resolution is described of a series of racemic trans-4-[5-(4-alkoxyphenyl)-2,5-dimethylpyrrolidine-1-oxyl-2-yl]benzoic acids (1), which are the key intermediates for the synthesis of chiral organic radical liquid crystalline compounds and are crystallized to give racemic compounds. Racemic acid 1 [(+/-)-1] with a long alkyl chain (C7 to C13) could be resolved by the conventional diastereomeric salt formation using (R)- or (S)-1-phenylethylamine (2) as the resolving agent, whereas resolution of (+/-)-1 with a short alkyl chain (C4 to C6) was unsuccessful. Use of six equiv of (R)- or (S)-2 for the initial diastereomeric salt formation of (+/-)-1 with a C7-C13 alkyl chain, followed by recrystallization of the resulting salts once or twice, gave 2S,5S- or 2R,5R-enriched 1, respectively, in an ee range of 75-92% and with an overall recovery of 11-27%, based on the original quantity of (+/-)-1.