Castanospermine in Leaves

Castanospermine is an indolizidine alkaloid obtained from the leaves of Castanospermum australe. It is known to be a potent inhibitor of glucosidase enzymes and possesses antitumor activity. Since it is a structural analog of a simple sugar molecule (Fig. 8), it is difficult to detect. Low volatility hampers separation by gas chromatography and lack of a chromophore makes sensitive HPLC analysis with photic detection impossible. 

However Donaldson et al. (1990) detected castanospermine with pulsed amperometric detection, which is a popular method for detecting carbohy- 

Castanospermine was detected with a triple-pulsed technique, which kept the electrode activity constant (Fig. 8). Castanospermine was first oxidized at a low positive electrode potential (El), and the current from the oxidation was measured at the end of the pulse, after the disturbing charging current had decayed. Then the electrode surface was cleaned by a high positive potential (E2), which oxidized the electrode surface, leading to desorption of absorbed oxidation products. The surface oxides were subsequently dissolved by a large negative potential (E3) that restored the pure metal surface and thus the activity of the electrode surface. One cycle took less than 1 s. 

This method was quite sensitive and selective. The detection limit in aqueous solution was 0.75 ng, and from plant material 2.5 ng of castanospermine could be detected. This method was also found to be suitable for the structurally related alkaloids 1-deoxynojirimycin, 1-deoxymannojirimycin, and swainsonine. 

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