Department of Preformulation, H. Lundbeck A/S, Copenhagen, Denmark.
Chirality. 2011 May;23(5):408-16. doi: 10.1002/chir.20943. Epub 2011 Apr 6.
The X-ray powder diffractograms of racemic citalopram oxalate and (S)-citalopram oxalate are very similar, but the melting point of the racemate is higher than that of the pure enantiomer. The higher melting point indicates that the racemate is a racemic compound, rather than a conglomerate. The crystal structure of the enantiomer contains two molecules of (S)-citalopram in the asymmetric unit. The conformation of the two molecules is different but they approximate mirror images of each other if the aromatic groups are interchanged. The crystal structure of the racemate is essentially isostructural with that of the enantiomer, having almost the same cell parameters but containing a crystallographic inversion centre that is not retained in the enantiomer structure. The closely-comparable crystal structures permit solid solutions to be formed between racemic and enantiomeric citalopram oxalate. Phase diagrams of the (R)-citalopram and (S)-citalopram oxalate system are constructed, and they show that solid solutions are formed at all ratios of the two enantiomers.
消旋西酞普兰草酸盐和(S)-西酞普兰草酸盐的 X 射线粉末衍射图非常相似，但外消旋体的熔点高于纯对映异构体。较高的熔点表明外消旋体是外消旋化合物，而不是外消旋混合物。对映异构体的晶体结构包含两个(S)-西酞普兰分子在不对称单位中。如果交换芳环基团，两个分子的构象不同，但彼此近似镜像。外消旋体的晶体结构与对映异构体基本等结构，具有几乎相同的晶胞参数，但含有一个在对映异构体结构中不保留的晶体学反演中心。非常相似的晶体结构允许在消旋和对映体西酞普兰草酸盐之间形成固溶体。构建了(R)-西酞普兰和(S)-西酞普兰草酸盐体系的相图，它们表明在两种对映异构体的所有比例下都形成了固溶体。
