Isosteviol preparation and inclusion complexation of it with γ-cyclodextrin

Isosteviol (Ist), a tetracyclic diterpenoid along with its structural derivatives, have received considerable attention due to its broad biological activities. Because of its low natural abundance, large scale utility of Ist has been limited. The present study described a method of preparing Ist using the typical Lewis acid approach, and the properties of its inclusion complex, namely γ-cyclodextrin/isosteviol (γ-CD/Ist), were also evaluated. Firstly, Ist was prepared from stevioside with Lewis acid. Fe3+ was the optimal catalyst and complete conversion of stevioside with a yield of 83.2% of Ist were obtained. To improve Ist aqueous solubility, γ-CD/Ist complexation was investigated. Results showed that aqueous solubility of Ist increased by 185-fold with an 1:1 γ-CD/Ist inclusion complex. At the ambient temperature, γ-CD/Ist complex aqueous solution maintained relatively unchanged at neutral and slightly higher pH values after 30 days. To our knowledge, the present study was the first such an effort on the preparation of Ist using Lewis acid and improvement of its solubility through γ-CD inclusion complex.