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)
Summary
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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