(191l) Isosteviol: Synthesis through Typical Lewis Acid-Catalysis (Fe3+) and Preparation Thereof Inclusion Complex with ?-CD

Diterpenoid isosteviol (Ist) and its derivatives have gained a growing interest for broad therapeutic benefits, especially in recent years. In this paper, a preliminary study on preparation of isosteviol with typical lewis acid and its inclusion complex, namely γ-cyclodextrin/isosteviol (γ-CD/Ist), were evaluated. Firstly, Ist was prepared from stevioside (Stv) with Lewis acid. Fe³⁺ was the optimal catalyst among five typical Lewis acid and the highest conversion of Stv of 100% and yeild of Ist of 83.2% were obtained based on the results of single factor experiments. In addition, in order to overcome Ist poor aqueous solubility, γ-CD/Ist was prepared by a co-evaporation method. The possible binding mode of Ist with α-CD, β-CD and γ-CD was identified using AutoDock software, respectively. Taking account of host molecular screening assay, γ-CD is the optimal host molecular. The solubility of Ist increased 185 folds at least, and formation of 1:1 γ-CD/Ist inclusion complex. HPLC, IR, TGA, XRD, SEM and NMR were evaluated for the γ-CD/Ist characterization. At ambient temperature, γ-CD/Ist complex aqueous solution is extremely stability with neutral and slight pH values after 30 days. To our knowledge, this is the first to prepare Ist using Lewis acid and improve thereof solubility through inclusion complex.