Preparation of biologically active compounds with high optical purity is very important in the pharmaceutical sciences, as different enantiomers or diastereomers exhibit different biological activity. For example, l-DOPA (3,4-dihydroxy-l-phenylalanine) is used in the management of Parkinson's disease, while the d–isomer does not exhibit such activity. The control of the chirality is also important in the field of material sciences, such as for liquid crystals.