藤田 正博

Shikimic acid was first isolated in 1885 by Eijkman from the fruit of the Japanese plant Illicium religiosum. Many natural plants contain shikimic acid for biosynthesis as an important intermediate. Roche pharmaceutical uses shikimic acid from star anise as a starting material for production of Tamiflu. However, isolation of star anise from natural resources has been limited. Here we report efficient and new isolation protocol of shikimic acid from Ginkgo biloba leaves utilizing an ionic liquid that dissolves cellulose. Shikimic acid was efficiently extracted and isolated from G. biloba leaves utilizing an ionic liquid 1-butyl-3-methylimidazolium chloride ([bmim]Cl), which is able to dissolve cellulose. Using the ionic liquid at 150 ℃ gave an extraction yield of 2.3% w/w for shikimic acid, which was 2.5 times higher than that for methanol at 80 ℃ (0.93% w/w). Meanwhile, an isolation protocol for obtaining shikimic acid in good yield from the IL phase using an anion-exchange resin Amberlite IRA-400 Cl form was established. The SEM micrograph of the leaves after extraction showed a significantly different morphology, with the larger features completely broken down into much smaller structures, indicating that the G. biloba leaves were much more highly dissolved in [bmim]Cl compared to in methanol The present procedure could lead to a convenient supply of shikimic acid, thus enabling production of greater amounts of the antiviral agent Tamiflu. The protocols are also likely to be applicable to other plant leaves, allowing for isolation of greater quantities of other natural products as well as unknown natural compounds.