Crystal Structure Prediction of Diastereomeric Salts:  A Step toward Rationalization of Racemate Resolution

Crystal structure prediction simulations were carried out to explore the solid state packing alternatives of two diastereomeric salts consisting of a chlorine-substituted cyclic phosphoric acid and the two enantiomers of ephedrine. The experimentally observed crystal structures were correctly simulated with an error of a few kcal/mol. This represents a significant achievement in crystal structure prediction due to the complexity of the mathematical search problem at hand (two distinct molecules in the asymmetric unit, one of which is flexible) and due to the complex energetics of these organic salts. In principle, these simulations show the way toward a truly predictive model for racemate resolution by preferential crystallization of diastereomeric salts.