GENERALISING THE CONCEPT OF OPTICAL RESOLUTION THROUGH CO-CRYSTALLISATION. K. Simon, Zs. Böcskei, K. Takács, Chinoin Pharmaceuticals, Budapest, Hungary; A. Mravik, D. Kozma, E. Fogassy, Technical University of Budapest, Hungary.

Diastereomeric salt formation is perhaps the most widely used technique for chiral resolution. Here we present a dozen crystal structures in which the principles of this classical method has been extended by utilising the intermolecular interactions between compounds which are not necessarily corresponding acid-base partners.

In our first example chiral acid was applied instead of a chiral base to separate a racemic acid by the mediation of a metal ion. Another case involves the resolution of an alcohol type compound with a chiral acid. A third example presents the investigation of small modifications of the resolving agent versus the efficiency of the resolution. Dramatically different resolving power of tartaric acid derivatives can be rationalised based on hydrogen bonding networks. In the last example we provide a structural explanation for an unsuccessful resolution experiment via camphorsulphonicacid. Due to the relative flexibility of the middle part of the base to be resolved both enantiomer base was found in the crystal structure in an approximate 1:2 ratio.

In conclusion the above examples clearly demonstrate the importance of investigating the entire crystal structure including minor interactions rather than just considering the most obvious salt forming hydrogen bonds.