Characterization of a new anhydrous form of Rotundine and its monohydrate

Rotundine is a chemical drug developed from Chinese traditional medicines that exhibits pseudopolymorphism. The anhydrous form and monohydrate are isolated and prepared via systemic crystallization screening, and the anhydrous form is reported for the first time. In this article single crystal X-ray diffractometry, powder X-ray diffractometry and FT-IR spectroscopy are used to characterize the Rotundine modifications. The analysis results show that the factors of crystal symmetry, intermolecular arrangements, conformational flexibility, hydrogen bonding interactions, and the incorporation of water finally lead to produce the polymorphic phenomenon. Via the in-vivo bioavailability of two forms, it is found that the new anhydrous form presents absorbable superiority relative to monohydrate, specifically Cmax and AUC of anhydrous form were approximately 1.5 times those of monohydrate. Study on the transformation of two forms show that they can convert to each other in certain conditions at solid state.