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United States Department of Agriculture

Agricultural Research Service

Title: Preparative Isolation of Swainsonine from Locoweed: Extraction and Purification Procedures

Authors
item Gardner, Dale
item Lee, Stephen
item Molyneux, Russell
item Edgar, John - CSIRO

Submitted to: Phytochemical Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 18, 2002
Publication Date: July 1, 2003
Citation: GARDNER, D.R., LEE, S.T., MOLYNEUX, R.J., EDGAR, J.A. PREPARATIVE ISOLATION OF SWAINSONINE FROM LOCOWEEDS: EXTRACTION AND PURIFICATION PROCEDURES. PHYTOCHEMICAL ANALYSIS. 2003.

Interpretive Summary: The alkaloid swainsonine is the toxin found in locoweeds (Oxytropis and Astragalus spp.). Swainsonine has potent -mannosidase inhibitory activity and chemotherapeutic potential and there is considerable interest in this compound by the biomedical research community. Swainsonine is commercially available but only at a considerable cost of $50 - $200 per milligram. The substance is difficult to synthesize and other natural sources require batch fermentation processes. This paper presents useful methods for isolation and purification of swainsonine from a natural source, locoweeds, in quantities large enough for practical use in chemical and biomedical research. The use of locoweed as source material for the swainsonine is attractive because large amounts of plant material can be collected, dried and stored, as opposed to the maintenance of batch fungal cultures. Although locoweed supplies may be geographically isolated and dependent on growth cycles, plant populations can easily be analyzed for swainsonine and those with the highest alkaloid content selected for extraction. The key isolation and purification step was a continuous liquid/liquid extraction procedure using methylene chloride to extract a basified aqueous/methanol (50/50) solution obtained after isolation of the polar base fraction by ion-exchange. Pure swainsonine was then obtained by recrystallization from ammonia-saturated chloroform or by sublimation. Smaller samples of swainsonine were also purified by formation of the chloroform-soluble methylboronate derivative, from which it could be regenerated easily by hydrolysis.

Technical Abstract: The trihydroxy indolizidine alkaloid swainsonine, a plant toxin with potent a-mannosidase inhibitory activity and chemotherapeutic potential, was isolated in gram quantities from locoweed (Astragalus lentiginous). The key isolation and purification step was a continuous liquid/liquid extraction procedure using methylene chloride to extract a basified aqueous/methanol (50/50) solution obtained after isolation of the polar base fraction by ionexchange. The concentration of swainsonine was increased from approximately 7% in the polar base material to 68% using the liquid/liquid extraction procedure. Pure swainsonine was then obtained by recrystallization from ammonia-saturated chloroform or by sublimation. Small samples of swainsonine were also purified by formation of the chloroform-soluble methylboronate derivative, from which it could be regenerated easily by hydrolysis.

Last Modified: 12/21/2014
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