A Study of Fasoracetam's Solid State Forms
Total Page：16
File Type：pdf, Size：1020Kb
Journal of Pharmaceutical Sciences xxx (2017) 1-5 Contents lists available at ScienceDirect Journal of Pharmaceutical Sciences journal homepage: www.jpharmsci.org Pharmaceutics, Drug Delivery and Pharmaceutical Technology A Study of Fasoracetam’s Solid State Forms: A Potential Anti-Alzheimer Pharmaceutical * Bram Harmsen 1, Koen Robeyns 1, Johan Wouters 2, Tom Leyssens 1, 1 Institute of Condensed Matter and Nanosciences, Universite Catholique de Louvain, Louvain-la-Neuve, Belgium 2 Namur Institute for Life Sciences (Narilis), University of Namur, Namur, Belgium article info abstract Article history: Different solid state forms of the research chemical fasoracetam, which counters the effects of Alz- Received 21 September 2016 heimer’s disease, have been subjected to a thermal and structural analysis. Single crystals were obtained Revised 21 December 2016 from solution evaporation and from the melt. Single-crystal X-ray analyses of the crystals show the Accepted 11 January 2017 existence of 2 hydrated and 1 non-hydrated crystalline form of fasoracetam. Under ambient conditions, the hydrate form I is found to be the most stable form, showing a melting point of 57C. This low melting point, combined with possible water losses could cause problems when formulating the hydrated form Keywords: and impact the storage conditions of the compound. polymorphism ® crystal structure © 2017 American Pharmacists Association . Published by Elsevier Inc. All rights reserved. thermogravimetric analysis calorimetry (DSC) solvent evaporation hydrate Alzheimer’s disease Introduction the thermodynamic relationships between these forms is also recommended, to avoid future issues related to phase trans- Fasoracetam (NS-105, 5-oxo-D-prolinepiperidinamide) is part formations, as illustrated by the Ritonavir and Rotigotine cases, of the racetam family, a drug of the pyrrolidone class and where a market withdrawal of the drug occurred due to phase currently considered a research chemical.1 The class is charac- transformations of the active pharmaceutical ingredient.19,20 terized by its nootropic (e.g., piracetam and fasoracetam), stim- Fasoracetam (Scheme 1) is a promising research chemical ulating (e.g., oxiracetam), and anticonvulsant (e.g., levetiracetam) and is available in solid form at ambient conditions. However, properties.2-6 Studies have shown promising results in its ability no crystal structure has yet been reported in the literature, nor to counter and reverse the effect of Alzheimer’sdisease.7-9 It is a any solid screen performed for this compound. The chemical known fact that the nature of a solid state form directly impacts structure of fasoracetam shows 2 amide functions which bioavailability,10,11 solubility12,13 and other pharmacokinetic commonly take part in hydrogen bonding patterns, as the parameters, which need to be controlled for maximum dosage carbonyl can serve as a hydrogen acceptor, whereas the amide effect and consistency. It is therefore important to exercise con- can act as a hydrogen donor. Having multiple hydrogen bonding trol over the solid phase form.14,15 Screening for different solid sites available, this could possibly lead to different packing phases of novel drugs has now become an integral part of the arrangements. Furthermore, other racetam compounds have drug development process.16,17 Additionally, legal instances still already shown a propensity toward the formation of multiple consider alternative solid forms as novel, hence a formulation solid state forms.21 with such a novel form would not infringe an existing patent.18 In this contribution, we therefore set out to identify different Besides identifying different solid forms, an understanding of solid state forms of fasoracetam and describe these from a struc- tural as well as a thermodynamical point of view. We identified a stable hydrated form (hydrate I), but also a second polymorphic This article contains supplementary material available from the authors by request form of the hydrate (hydrate II). Using specific conditions, an or via the Internet at http://dx.doi.org/10.1016/j.xphs.2017.01.016. anhydrated form could also be isolated. All forms are structurally * Correspondence to: Tom Leyssens (Telephone: þ32-10-47-28-11; Fax: þ32-10- 47-27-07). described and a full thermodynamic analysis on all forms was E-mail address: [email protected] (T. Leyssens). performed. http://dx.doi.org/10.1016/j.xphs.2017.01.016 ® 0022-3549/© 2017 American Pharmacists Association . Published by Elsevier Inc. All rights reserved. 2 B. Harmsen et al. / Journal of Pharmaceutical Sciences xxx (2017) 1-5 Scheme 1. Chemical structure of fasoracetam. Materials and Methods Materials Figure 1. Fasoracetam powder patterns simulated from SC-XRD. Fasoracetam was ordered from Jinan HaoHua Industry Co., Ltd., and used as received. It was identified via X-ray powder diffraction crystals. The anhydrate form could not be crystallized from any of to be the most stable form of the hydrate (hydrate I). the solvents used. To obtain this form, a recrystallization from the All solvents used were obtained from VWR International S.A.S. melt was performed in vacuo, where it was kept at 60C for 1 week. and used without further purification. These conditions allowed water to be removed from the melt. After a 1-week period the temperature was lowered while maintaining Methods vacuum conditions, which resulted in a different solid form, the anhydrate, with crystals suitable for SC-XRD analysis. Starting from Single-crystal x-ray diffraction (SC-XRD) experiments were hydrates I and II, both convert into the same anhydrated form using collected on a mar345image plate using MoKa radiation(Rigaku Ultra the method described above. X18S generator, Fox3D mirrors). Crystals were picked up using a little In this contribution, we also present a solid form screen of grease, and for low temperature experiments (Table 2) the crystal was fasoracetam. Even though the screen is limited, 3 different forms of fasoracetam have been identified. Initially, a first screen was flash frozen in an N2 flow prior to data collection. Data images were integrated by CrysAlisPRO22 and the implemented multi-scan ab- performed based on the solvent evaporation principle. The sorption correction was applied. All structures were solved by purchased compound was dissolved in the solvents investigated SHELXS-97 and refined by SHELXL-2014/7.23 All non-hydrogen atoms and the solution was left to evaporate completely. were refined anisotropically and H-atoms were placed on calculated positions with isotropic temperature factors 1.2 times Ueq of their Results and Discussion parent atoms. For the anhydrate structure, the piperidine rings were found to be disordered with the minor fraction <10%. The minor part Form Screening was restrained to be similar (bond and angles) to the main fraction. Molecular structures were created using mercury.24 Once the solution was evaporated completely, the powders Powder x-ray diffraction (XRPD) measurements were performed obtained from the solvent screen were directly analyzed using on a Siemens D5000 diffractometer equipped with a Cu X-ray source XRPD (experimental patterns can be found in Supplementary operating at 40 kV and 40 mA. A secondary monochromator allowed Information, Section 1). The different solid state forms obtained the selection of Ka radiation of Cu (l ¼ 1.5418 Å). A scanning range of are shown in Figure 1 and it was later confirmed that 2 forms are 2q values from 2 to 72 at a scan rate of 0.6/min was applied. polymorphically related (hydrate I and II, respectively), which are Differential scanning calorimetry (DSC) measurements were both a 1:1 hydrated form. The results obtained are shown in Table 1. performed on a Mettler Toledo DSC821e using 40 mL aluminum Solvent evaporation does not lead to the formation of an anhy- crucibles without pin, with the method increasing from 25C to drate form, but instead 2 different hydrates were found via XRPD. 250C with a step size of 10C/min under continuous nitrogen flow. The hydrate form obtained from each solvent appears to be random, The method used to determine the melting points can be found in as no correlation among evaporation rate, hygroscopicity, and po- Supplementary Information, Section 3. larity can be found.25,26 Crystals obtained by water and methanol Thermogravimetric analysis (TGA) measurements were per- evaporation were found suitable for SC-XRD analysis, which showed formed on a Mettler Toledo TGA/SDTA851e using an aluminum a 1:1 stoichiometric hydrate form in both cases, named hydrate I and crucible, with the method increasing from 25C to 350C with a step hydrate II, respectively. As will be shown later, hydrate I has a size of 10C/min while maintaining a nitrogen flow of 50.0 mL/min. melting point at 57C and hydrate II has a melting point at about 48C. A structural analysis of all hydrogen bonding patterns is given Single Crystal Growth and Form Screening below, followed by a thermal analysis. The single crystals obtained for SC-XRD analysis were grown via Structural Analysis different methods. Initially, fasoracetam (as received, hydrate form I) was recrystallized from water using solvent evaporation. Figure 2 shows the hydrogen bonding pattern for the anhydrate R2 The second hydrate, form II, is less stable and was obtained from phase. This bonding network corresponds to an 2(9) synthon methanol evaporation, which provided large enough single (Etter’s graph set notation27), composed of a N-H group of the B. Harmsen et al. / Journal of Pharmaceutical Sciences xxx (2017) 1-5 3 Table 1 Solvent-based Solid Form Screen for Fasoracetam Solvent Crystal Form (XPRD) Water Hydrate I Acetonitrile Hydrate II Methanol Hydrate II Ethyl acetate Hydrate I Acetone Hydrate I Dichloromethane Hydrate II Tetrahydrofuran Hydrate I Chloroform Hydrate II Toluene Hydrate II XPRD, x-ray powder diffraction. pyrrolidone ring of the first molecule forming a hydrogen bond with the pyrrolidone carbonyl of a second molecule. A second hydrogen bond links the bridging carbonyl of the first molecule to the N-H group in the pyrrolidone ring of the second molecule.