Izidine alkaloids cover compounds, which contain one of the izidine skeletons. There are three different skeletons in this group: pyrrolizidine, indolizidine and quinolizidine. Izidine alkaloids are, therefore, compounds with a bicyclic nucleus, which have different a, 0, y and x. Izidines present structural similarities, but organic and functional differences. These alkaloids include more than 800 compounds. Several of them show interesting physiological and pharmacological behaviour. Izidine alkaloids with the pyrrolizidine nucleus (e.g., hel-losupine, senecionine, retronecine, acetyl-intermedine, acetyl-lycopsamine and indicine-N-oxide) are toxic and known to affect the liver24. Izidine alkaloids containing the indolizidine nucleus (e.g., slaframine, elaeocanine, securitinine, tylophorine, swansonine and castanospermine) play an important role as actual and potential drugs in the fight against viruses, including AIDS. Some of these compounds, for example, pumiliotoxin B, have an ecological function in nature. Izidine alkaloids with the quinolizidine nucleus (e.g., lupinine, lusitanine, lam-prolobine, angustifoline, lindenianine, sparteine, lupanine, nuttalline, aphylline, sophoridine, isomatrine, albertidine, aloperine and nitraramine) contain toxic compounds with strong selective ecological impact7.
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