Spectrophotometric studies of a novel Gedunin-2-Hydroxypropyl- ß-cyclodextrin binary system.

ABSTRACT

BACKGROUND: Gedunin, a limonoid, is linked with antimalarial, anticancer and anti-allergic activities. This study was aimed at preparing an inclusion complex of gedunin and 2-hydroxypropyl-p-cyclodextrin (HBD) to increase solubility of-gedunin in polar solvents which will increase absorption and bioavailability in vivo and thus enhance pharmacological effects. MATERIALS AND METHODS: Gedunin was obtained from the hexane extract of Entandrophragma angolense heartwood by column and preparative thin layer chromatography. The structure was previously confirmed by spectroscopic means (NMR). The electronic absorption spectra data of the complexes formed between gedunin. and HBD in various solvents was determined using the UV-VIS spectrophotometer. The stoichiometry of inclusion was determined by Job's method of continuous variation. RESULTS: Evidence of interaction was observed between gedunin and HBD in the various solvents but gedunin and its complex with HBD exhibited sharp absorption bands in acetate buffer (pH 3.5).The spectrophotometric titrations showed curves with a single point of inflexion when the experiment was carried'out at 25°C (298 K) and 37°C (310 K). A stoichiometric ratio of 11 for complex formation was obtained. The formation constants (K,) obtained at 25°C and 37°C.were 9.539 x.10³ M⁻¹ and .1.853 x 104 M⁻¹ respectively. Thermodynamic considerations revealed hydrophobic interaction between gedunin and HBD. CONCLUSION: A stable inclusion complex of gedunin and HBD was formed at room and body temperature. This complex formation involved trapping of poorly soluble gedunin into the hydrophobic core of the cyclodextrin and may enhance the pharmacological activity of gedunin in vivo.