One hydrogen bond does not a separation make, or does it? Resolution of amines by diacetoneketogulonic acid

Abstract

Diacetoneketogulonic acid was used to separate primary amines from their racemic modifications and the selectivity of the acid was rationalized by lattice energy calculations and analyzing the weak interactions around the captured amines. Selectivity arises from the phenomenon of molecular recognition and depends on such factors as complementarity of binding sites, the strengths of the relevant non-bonding interactions between the reactants and the conformational adaptability of the molecules. Supramolecular selectivity, whereby a host shows preference for a particular guest and separates it from a mixture, is relevant in many applications, such as petroleum chemistry or pharmaceutics. In this way one can segregate a given constitutional isomer from a solution containing several components which have similar boiling points (e.g. xylene isomers,1 tautomers2) where distillation techniques would be inefficient. A most demanding form of separation is that of enantiomeric resolution. This because the physical properties of the R and S forms of the two optical isomers have identical characteristics such as melting point, boiling point, vapour pressure and density and differ only in their reactions toward homo-chiral compounds and polarized light. Resolution of racemic modifications of organic molecules is of considerable importance to the pharmaceutical industry because 90% of drugs currently used are chiral.