Abstract

The solubility of trihexyphenidyl (Thp) was improved by its combination with β-cyclodextrin (β−CD) and modified β-CDs. The solubility of Thp was found to be increased in the presence of β-CD, hydroxypropyl-β-cyclodextrin (HP-β-CD), methyl-β-cyclodextrin (Me-β-CD) and sulfobutylether-β-cyclodextrin (SBE-β-CD). In particular, the solubility of Thp in conjunction with SBE-β-CD was increased by a factor of 11. The formation constant (Kc) for the Thp/SBE-β-CD inclusion complex was determined to be 2300 L/mol based on fluorometry data. The structure of the Thp/SBE-β-CD complex in aqueous solution was examined by 1H-1H rotating frame nuclear Overhauser effect spectroscopy (ROESY) NMR, and the phenyl moiety of the Thp was found to coordinate with the secondary hydroxyl face of the SBE-β-CD. A solid Thp/SBE-β-CD inclusion complex was prepared by freeze-drying.

Highlights

  • Trihexyphenidyl (Thp) is a pharmaceutical compound that has been shown to improve various disease symptoms, including muscle rigidity, finger tremors and depression, by regulating the release of adrenaline.Natural cyclodextrins (α, β- and γ-CD) are widely used in many fields since they readily form inclusion complexes with a variety of organic compounds (Saenger 1980; ÖZdemir and Ordu 1998; Reineccius et al 2002)

  • We investigated the solubility of inclusion complexes of Thp with natural and modified CDs at constant pH

  • The results demonstrate that the formation of inclusion complexes of the sunscreen agents and β-CD can inhibit the photodegradation (Al-Rawashdeh et al 2010, 2013)

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Summary

Introduction

Natural cyclodextrins (α-, β- and γ-CD) are widely used in many fields since they readily form inclusion complexes with a variety of organic compounds (Saenger 1980; ÖZdemir and Ordu 1998; Reineccius et al 2002). Β-cyclodextrin (β-CD) is used to suppress the bitterness of antihistamine drugs in solution through the formation of inclusion complexes (Hibi et al 1984; Ono et al 2011). Β-CD exhibits relatively low solubility in water, which limits its applications in pharmaceutical formulations. Various CD derivatives have been synthesized to extend the potential applications (Uekama 1985; Szejtli 1992; Loftsson and Duchêne 2007). We have previously reported complexes of α-lipoic acid and melatonin with modified CD derivatives (Maeda et al 2010, 2013), and determined that the solubilities of α-lipoic acid and melatonin in the

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