Crystal Engineering Approach To Forming Cocrystals of Amine Hydrochlorides with Organic Acids. Molecular Complexes of Fluoxetine Hydrochloride with Benzoic, Succinic, and Fumaric Acids

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Abstract
A crystal engineering strategy for designing cocrystals of pharmaceuticals is presented. The strategy increases the probability of discovering useful cocrystals and decreases the number of experiments that are needed by selecting API:guest combinations that have the greatest potential of forming energetically and structurally robust interactions. Our approach involves multicomponent cocrystallization of hydrochloride salts, wherein strong hydrogen bond donors are introduced to interact with chloride ions that are underutilized as hydrogen bond acceptors. The strategy is particularly effective in producing cocrystals of amine hydrochlorides with neutral organic acid guests. As an example of the approach, we report the discovery of three cocrystals containing fluoxetine hydrochloride (1), which is the active ingredient in the popular antidepressant Prozac. A 1:1 cocrystal was prepared with 1 and benzoic acid (2), while succinic acid and fumaric acid were each cocrystallized with 1 to provide 2:1 cocrystals of fluoxetine hydrochloride:succinic acid (3) and fluoxetine hydrochloride:fumaric acid (4). The presence of a guest molecule along with fluoxetine hydrochloride in the same crystal structure results in a solid phase with altered physical properties when compared to the known crystalline form of fluoxetine hydrochloride. On the basis of intrinsic dissolution rate experiments, cocrystals 2 and 4 dissolve more slowly than 1, and 3 dissolves more quickly than 1. Powder dissolution experiments demonstrated that the solid present at equilibrium corresponds to the cocrystal for 2 and 4, while 3 completely converted to 1 upon prolonged slurry in water.

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