Chiral discrimination upon crystallisation of the diastereomeric salts of 1-arylethylamines with mandelic acid or p-methoxymandelic acid: interpretation of the resolution efficiencies on the basis of the crystal structures

Abstract

The crystal structures of the diastereomeric salts of 1-arylethylamines with mandelic acid or p-methoxymandelic acid have been studied. This revealed that there was correlation between the efficiencies of the optical resolutions of the amines with the resolving reagents and the crystal structures of the salts. A characteristic hydrogen-bond layer, consisting of stable columnar structures and having a planar boundary surface, was found to be common to the less-soluble salt crystals; these crystals were considered to be stabilised from the viewpoint of both their hydrogen-bonding and van der Waals interactions. In contrast, in the corresponding more-soluble salts and in those diastereomeric salts which could not be separated by crystallisation, no such particularly stabilised crystal structure was formed; there only existed either columnar structures or planar boundary surfaces in these crystals. These results strongly suggest that for successful resolution it is necessary to realise a hydrogen-bond layer, consisting of stable columns and having planar boundary surfaces, in the crystals of one of the pair of diastereomeric salts. In order to achieve such a crystal structure, complementarity in molecular length between a target racemate and a resolving reagent must be considered the most important and fundamental factor.

Multicomponent Organic Alloys Based on Organic Layered Crystals

“…The sterically complementary pairs, for example, C3/C7 and C4/C6 for C3C4C6C7ss, have the same width in the alkyl bilayer structure, which provided the closest packing in the alkyl bilayer structure, and made them flat to form the twodimensional hydrogen-bond network among the ion pairs and CH-p/p-p interactions between the naphthalene rings. [14] Furthermore, these results suggested random arrangement of the pairs. There are two hypothetical models to provide the averaged d spacing: a random model [20d] and a staged model [20d] (Figure 4).…”

“…For example, they are used for optical resolution of racemic acids or bases, [12][13][14] crystalline-state reactions, [15] topochemical polymerizations, [16] host-guest crystals, [17] and so on. Salt formation has some advantages for crystal engineering: easy preparation, various combinations, and strong intermolecular interactions between the ion pairs, such as hydrogen bonds and electrostatic interactions.…”

Chiral discrimination of 2‐arylalkanoic acids by (1S,2S)‐1‐aminoindan‐2‐ol and (1S,2S)‐2‐aminoindan‐1‐ol: Correlation of the relative configuration of the amino and hydroxy groups with the pattern of a supramolecular hydrogen‐bond network in the less‐soluble diastereomeric salt

“…[2][3][4] The crystal structure of less-soluble (1S,2S)-2⅐(S)-6b is shown in Figure 1. In the crystal of (1S,2S)-2⅐(S)-6b, a columnar hydrogen-bond network is constructed, as was found in the less-soluble salts in our previous studies;…”

“…[2][3][4] In order to compare the re- sults as objectively as possible, the crystallization conditions such as solvent and temperature were arranged. The results are summarized in Tables 1 and 2.…”

“…On the other hand, in the course of our continuous studies on the design of acidic resolving agents, we have found that the formation of a supramolecular hydrogen-bond sheet in the less-soluble salt is an essentially important factor for the successful resolution of 1-arylalkylamines with enantiopure arylglycolic acids. 3,4 Comparing the two hydrogen-bond structures with each other, the supramo- …”