Graduation Year

2011

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Chemistry

Major Professor

Mike J. Zaworotko

Keywords

Crystal Engineering, Pharmaceutical Cocrystal, Pharmacokinetics, Physicochemical Properties, Zwitterion

Abstract

Enhancing the physicochemical properties of solid-state materials through crystal engineering enables optimization of these materials without covalent modification. Cocrystals have become a reliable means to generate novel crystalline forms with multiple components and they exhibit different physicochemical properties compared to the individual components. This dissertation exemplifies methodologies to generate cocrystals of active pharmaceutical ingredients (API's) based upon knowledge of supramolecular interactions (supramolecular synthons), while focusing on enhanced delivery through in vitro and in vivo processes with both salts and cocrystals respectively.

The utility of mechanochemistry involving small amounts of an appropriate solvent, or solvent drop grinding (SDG), has been shown to reliably reproduce cocrystals with the anti-convulsant carbamazepine that were originally obtained by solution crystallization. This technique has been confirmed as a reliable screening method using solvents in which both components exhibit some solubility. The benefits of this technique lie in the time and cost efficiency associated with it as well as its inherently small environmental impact making it a "Green" method. SDG was also used as an efficient way to discover cocrystals of the anti-inflammatory meloxicam with carboxylic acids after analysis of existing reports and the analysis of structural data from the Cambridge Structural Database (CSD) to guide the choice of coformer. It has been shown that SDG can be used to screen for cocrystalline forms that are also obtainable by solution crystallization which is important in later stage development and manufacturing including but not limited to large scale up processes. Single crystals suitable for single crystal X-ray diffraction were obtained with meloxicam and two of the coformers, fumaric and succinic acid. Some of the meloxicam cocrystals exhibited enhanced pharmacokinetic (PK) profiles in rats exemplifying significantly higher serum concentrations after only fifteen minutes and consistently higher exposure over the time studied while others maintained lower exposure. This reveals that cocrystals can fine tune the PK profile of meloxicam in order to reduce or enhance exposure.

Two different sulfonate salts, 4-hydroxybenzenesulfonate (p-phenolsulfonate) and 4-chlorobenzenesulfonate, of the anti-spastic agent (R,S) baclofen were developed by strategically interrupting the intramolecularly stabilized zwitterionic structure of baclofen. This zwitterionic structure results in low solubility associated with physiological pH required for intrathecal administration. Structural data for both salts in the form of single crystal X-ray diffraction data was successfully obtained. Solubility based on baclofen was assessed and shown to increase in pure water and at pH's 1 and 7. Only the 4-chlorobenzenesulonate salt maintained an increased solubility over two days at pH 7 making it a viable candidate for further study in terms of intrathecal administration. During crystallization experiments with (R,S) baclofen two polymorphic forms of the baclofen lactam were generated, Forms II and III. Both forms are conformational polymorphs confirmed by single crystal X-ray diffraction and Form II has a Z' of 4 with an unusual arrangement of enantiomers.

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