This article discusses differences in physicochemical properties such as solubility and melting point between (S)-thalidomide and (RS)-thalidomide based on crystal structures determined by X-ray diffraction experiments. Investigation of such differences is of great importance because thalidomide has attracted considerable attention again due to its wide-range bioactivity for intractable diseases. In this article, structures of hydrogen-bonded rings were compared between asymmetric homochiral dimers in (S)-thalidomide crystal and symmetric heterochiral dimers in (RS)-thalidomide crystal. The heterochiral dimer was evaluated to be more stable than the homochiral dimer by the energy calculations for hydrogen-bonded rings in those dimers. These results indicate that differences in physicochemical properties between enantiomeric and racemic thalidomides originate from the difference of structural stability between homochiral and heterochiral dimers.
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