Mihály Nógrádi

Separation of non-racemic mixtures of enantiomers: an essential part of optical resolution

Non-racemic enantiomeric mixtures form homochiral and heterochiral aggregates in melt or suspension, during adsorption or recrystallization, and these diastereomeric associations determine the distribution of the enantiomers between the solid and other (liquid or vapour) phases. That distribution depends on the stability order of the homo- and heterochiral aggregates (conglomerate or racemate formation). Therefore, there is a correlation between the binary melting point phase diagrams and the experimental ee(I)vs. ee(0) curves (ee(I) refers to the crystallized enantiomeric mixtures, ee(0) is the composition of the starting ones). Accordingly, distribution of the enantiomeric mixtures between two phases is characteristic and usually significant enrichment can be achieved. There are two exceptions: no enrichment could be observed under thermodynamically controlled conditions when the starting enantiomer composition corresponded to the eutectic composition, or when the method used was unsuitable for separation. In several cases, when kinetic control governed the crystallization, the character of the ee(0)-ee(I) curve did not correlate with the melting point binary phase diagram.

Synthesis of new optically active pyridino- and pyridono-18-crown-6 type ligands containing four lipophilic chains

Highly lipophilic enantiomerically pure pyridino- and pyridono-18-crown-6 type ligands containing four stereogenic centers to which butyl or butoxymethyl groups are attached have been synthesized. X-Ray analysis of the (R)-1-phenylethylammonium and benzylammonium perchlorate complexes of the unsubstituted pyridono ligand revealed, that, in contrast to the free ligand, in the complex the hydroxypyridine tautomer is present.

About the existence of padmakastein and padmakastin. The synthesis of 4′,5-dihydroxy-7-methoxyisoflavanone and its 4′-glucoside

Abstract The title compounds have been prepared by hydrogenation of the corresponding isoflavones and found to differ from padmakastein and padmakastin, isolated, from Prunus puddum and reported as 4′,5-dihydroxy-7-methoxyisoflavanone and its 4′-glucoside.