Seeds of the Moreton Bay chestnut, Castanospermum australe, a tree from the rainforests of Queensland, Australia. The seeds contain castano- spermine, one of a class of compounds, nicknamed sugar-shaped alkaloids, which can inhibit the enzymes that normally break down chains of sugars. Castanospermine is an analogue of glucose, it powerfully suppresses the alpha-glucosidase found in the guts of mammals, rendering the Moreton Bay chestnut indigestible. Researchers investigating possible future applications for the sugar-shaped alkaloids have shown that castanospermine reduces the ability of the human immunodeficiency virus, which causes AIDS, to infect cultured cells.