Separation of racemate from excess enantiomer of chiral nonracemic compounds via density gradient ultracentrifugation

In this study, it is shown that preparative density gradient ultracentrifugation can be applied to separate racemate crystals from excess enantiomer crystals. This was demonstrated for alanine crystals separated in a 50 wt % Nycodenz gradient. The recovery rates of the pure enantiomers from the mixtures were good (70-90%), and the separation method showed accuracy in the third digit of the density. As such density differences between racemate and enantiomers can be found for a wide range of crystalline chiral compounds, the presented separation method should be applicable to a large variety of substances on a preparative scale.