Chiral Crystallization of Optically Inactive Indolyl Sulfonamides Caused Through the Combination of Specific Intermolecular Interactions

Key points of the presentation
The researchers found that optically inactive indolyl sulfonamides (benzenesulfonamide derivatives of indoleamine) formed optically active crystals at an unusually high proportion compared with other common compounds via the process of chiral crystallization.
The chiral crystallization in indolyl sulfonamides was affected by the specific type of interaction between molecules in the crystal. This was demonstrated by a comprehensive analysis using M_chiral, the ratio of chirality identities of molecules linked by interactions proposed by the authors.
In the crystal, the most dominant interactions between the indolyl sulfonamide molecules are two types of hydrogen bonds: hydrogen bonding interactions between the sulfonamide proton and the sulfonyl group of the sulfonamide, and hydrogen bonding interactions between the NH proton of the indole and the sulfonyl group of the sulfonamide. The high proportion of chiral crystallization is thought to be mainly due to the combination of these two types of hydrogen bonds. Furthermore, among the intermolecular interactions other than those mentioned above, the CH…π interaction was favorable for chiral crystallization, whereas the interaction between the hydrogen bond and π…π was not.