Rare Case of Polymorphism in a Racemic Fluoxetine Nitrate Salt: Phase Behavior and Relative Stability

详细信息    查看全文

• 作者：Paulo S. Carvalho Jr. ; Javier Ellena ; Dmitry S. Yufit ; Judith A. K. Howard
• 刊名：Crystal Growth & Design
• 出版年：2016
• 出版时间：July 6, 2016
• 年：2016
• 卷：16
• 期：7
• 页码：3875-3883
• 全文大小：594K
• 年卷期：0
• ISSN：1528-7505

文摘

Polymorphism in racemic pharmaceutical compounds is relatively unexplored. However, this phenomenon may provide an additional tool to crystal engineering, opening the doors to rational design of chiral resolution, chiral enrichment, and chiral purification of pharmaceutical compounds. In this work we report two racemic polymorphs occurring for the nitrate salt of the antidepressant drug fluoxetine (FLX): a racemate (P2<sub>1sub>/n, Z = 4, Z′ = 1) and a kryptoracemate (Pca2<sub>1sub>, Z = 4, Z′ = 2). The relative stability of these polymorphs was established through a combination of techniques, namely, differential scanning calorimetric (DSC), thermogravimetric analysis (TGA), hot stage microscopy (HSM), and solubility measurements. Though the two polymorphs share some structural features, the N<sup>+sup>–H···O<sup>–sup> hydrogen bonds have created dissimilar racemic motifs in their packing, resulting in different enantiomer orientations. The racemate is more stable over the temperature ranges we studied and is monotropically related to kryptoracemate. In our experiments, the obtaining of non-centrosymmetric lattice of racemic fluoxetine nitrate was shown to be dependent on kinetic factors. The thermodynamic relationships between both polymorphs were further confirmed by measuring their water solubility at 20 and 37 °C.