Effect of position isomerism on the formation and physicochemical properties of pharmaceutical co-crystals.
The effect of position isomerism on the co-crystals formation and physicochemical properties was evaluated. Piracetam was used as the model compound. Six position isomers, 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-dihydroxybenzoic acid (DHBA), were used as the co-crystal formers. Co-crystals were prepared on a 1:1 molar ratio by crystallization from acetonitrile. The solid-state properties of co-crystals were characterized using X-ray powder diffractometry (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR). All co-crystal formers formed co-crystal with piracetam except 2,6-DHBA. This failure was possibly due to steric hindrance of two bulk hydroxyl groups and preference of intra-molecular hydrogen bonding formation between hydroxyl group and carboxylic acid group. The XRD patterns of resulting co-crystal indicated that they are highly crystalline and different than parental compounds. Based on the single crystal data, P_23DHBA is orthorhombic while P_24DHBA, P_34DHBA, and P_35DHB belong to monoclinlic system. The hydrogen bonding network patterns of the co-crystals are also different. DSC data showed that the melting temperatures of resulting co-crystals are all lower than that of the starting materials. The melting point rank order of the co-crystals is: P_24DHBA > P_34DHBA > P_23DHBA > P_25DHBA > P_35DHBA.
Liao
Xiangmin
X
Forest Laboratories, Inc, 49 Mall Drive, Commack, New York 11725, USA. xiangmin.liao@frx.com
Gautam
Mohan
M
Grill
Andreas
A
Zhu
Haijian Jim
HJ
D002152:Calorimetry, Differential Scanning; D055598:Chemical Phenomena; D003460:Crystallization; D007536:Isomerism; D004364:Pharmaceutical Preparations / Q000737:chemistry*; D010889:Piracetam / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D014961:X-Ray Diffraction
D004364:Pharmaceutical Preparations; D010889:Piracetam