Structural Diversity of Brexpiprazole and Related Analogues: Impact on Solubility and Drug Delivery

Brexpiprazole (BPZ) is an atypical antipsychotic drug indicated for the treatment of schizophrenia and depression. Crystal form screening of BPZ resulted in the formation of three polymorphs (I, II, and III), two methanol solvates, a toluene hemisolvate, and a dihydrate. Thermal analysis and solvent...

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Bibliographic Details
Published in:Crystal growth & design 2018-04, Vol.18 (4), p.2326-2334
Main Authors: Zeidan, Tarek A, Tilak, Pranoti A, Trotta, Jacob T, Curran, Erin, Oliveira, Mark A, Chiarella, Renato A, Almarsson, Örn, Hickey, Magali B
Format: Article
Language:English
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Summary:Brexpiprazole (BPZ) is an atypical antipsychotic drug indicated for the treatment of schizophrenia and depression. Crystal form screening of BPZ resulted in the formation of three polymorphs (I, II, and III), two methanol solvates, a toluene hemisolvate, and a dihydrate. Thermal analysis and solvent-mediated conversion experiments of the three unsolvated polymorphs established that Form I is the thermodynamically stable form at ambient temperature. All three polymorphs are monotropically related, whereby Forms I and II are the most and least stable forms, respectively. Structural diversity of BPZ was compared with two chemically related analogues, aripiprazole (APZ) and its active metabolite dehydro-aripiprazole (dAPZ). Like APZ and dAPZ, BPZ was shown to form a thermodynamically stable, hydrated crystal form when exposed to an aqueous environment; however, while APZ and dAPZ were characterized as monohydrates, BPZ is a dihydrate. The crystal structure of BPZ dihydrate (S2H2O) showed two water molecules connecting two BPZ molecules, with hydrogen bonding occurring between both the piperazine nitrogen and the oxygen of the carbonyl moiety with different water molecules. Despite the chemical similarity of BPZ, APZ, and dAPZ, comparison of all accumulated crystal structures reveals wide structural diversity, with a significant impact on physicochemical properties. In particular, the solubility of BPZ is significantly lower in water across the physiologically relevant pH range. Implications to drug delivery of these findings are discussed.
ISSN:1528-7483
1528-7505
DOI:10.1021/acs.cgd.7b01747