Cyanobacteria neurotoxic alkaloids

Cyanobacterial neurotoxins are small ringed alkaloids and have dramatic effects on various components of vertebrate neurons. They are all water soluble and are synthesized by several cyanobacterial genera (Table 5.1). The most commonly isolated neurotoxins are the paralytic shellfish toxins, although several other potent neurotoxic alkaloids are synthesized by freshwater cyanobacteria (Table 5.1). 

Neurotoxic Alkaloids of Principally Freshwater and Terrestrial Cyanobacteria 141... 

In particular. Section I describes the structures and biological activities of selected classes of alkaloids. Almost half of the chapters focus their attention on terrestrial alkaloids (Chapters 1-5). The other half (Chapters 7-11) describe recent results in the field of marine alkaloids, whUe Chapter 6 is focused on neurotoxic alkaloids produced by cyanobacteria, microorganisms living in both marine and terrestrial environments. The particular emphasis on marine alkaloids undoubtedly reflects our long-standing research activity on marine metabolites, but it is also a result of the impressive amount of work carried out in the last few decades on marine natural product chemistry. Section II (Chapters 12-15) gives an account of modern techniques used for the detection and structural elucidation of alkaloids, while Section III is divided into two parts different methodologies for the synthesis of alkaloids and accounts of modem biosynthetic studies. 

Cyanobacteria known to produce hepatotoxins include species of Microcystis (32-36), Anabaena (37-40), Nostoc (41,42), Oscillatoria (43,44) and the brackish water Nodularia spumigena (45,46). These cyanobacteria produce a wide range of toxins including neurotoxic alkaloids, lipopolysaccharides, phenolic compounds and most importantly, the cyclic hepatotoxic peptides microcystins and nodularins. Since both microcystins and nodularins were recently discovered even in shellfish (47) and tropical fish species (48), and a nodularin variant was isolated in Papua New Guinea also from the tropical marine sponge Theonella swinhoei (49), marine prokaryotes are apparently producing identical toxins as the cyanobacteria. However, since this nodularin variant was isolated from a marine sponge it may well be produced by a microbial symbiont. 

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