Polymorph Selection and Derivatization in Enantiomerically Pure Medicarpin: Crystallographic and Computational Insights

Polymorphism critically influences the solid-state properties of organic molecules, affecting stability, solubility, and functionality. We investigated the polymorphic behavior of enantiomerically pure (+)-(6aS,11aS)-medicarpin through combined experimental and computational analyses. Single-crystal X-ray diffraction revealed two distinct chiral polymorphs: the previously reported monoclinic P21 form and a newly identified orthorhombic P212121 form with a fully chiral packing arrangement. The discovery of this previously unreported polymorph underscores the subtle yet decisive effects of solvent and conformational flexibility in directing crystallization. Detailed structural analysis reveals that, whereas the P21 form is only stabilized by a single dominant electrostatic interaction, the P212121 form features a more complex network comprising C-H···π contacts, bifurcated C-H···O hydrogen bonds, and aromatic edge-to-face interactions. Further investigation of a functionalized p-nitrobenzoate derivative corroborates the critical influence of molecular substituents and crystallization conditions on packing motifs. Lattice energy DFT calculations confirm that each polymorph is stabilized by distinct electrostatic and dispersive interaction patterns, illustrating the complex energetic landscape of polymorph selection. Altogether, this work provides a framework for understanding and anticipating which polymorph is likely to form under specific solvent and crystallization conditions, offering insights for future strategies in materials design and guiding the pursuit of patentable crystalline forms in pharmaceutical applications.