Abstract
The cyanobacteria are well recognized as producers of a wide array of bioactive metabolites including toxins, and potential drug candidates. However, a limited number of taxa are generally considered with respect to both of these aspects. That said, the order Stigonematales, although largely overlooked in this regard, has become increasingly recognized as a source of bioactive metabolites relevant to both human and environmental health. In particular, the hapalindoles and related indole alkaloids (i.e., ambiguines, fischerindoles, welwitindolinones) from the order, represent a diverse, and phylogenetically characteristic, class of secondary metabolites with biological activity suggestive of potential as both environmental toxins, and promising drug discovery leads. The present review gives an overview of the chemical diversity of biologically active metabolites from the Stigonematales—and particularly the so-called hapalindole-type alkaloids—including their biosynthetic origins, and their pharmacologically and toxicologically relevant bioactivities. Taken together, the current evidence suggests that these alkaloids, and the associated cyanobacterial taxa from the order, warrant future consideration as both potentially harmful (i.e., “toxic”) algae, and as promising leads for drug discovery.
Highlights
Cyanobacteria are ubiquitous in the environment, but arguably best recognized as the conspicuous “blue-green algae” in freshwater and coastal habitats, and in association with eutrophication and episodic “harmful algal blooms” (HABs)
Among studies of bioactive metabolites from cyanobacteria, the order Stigonematales remains relatively underrepresented with regards to both environmental health and biomedical aspects
An drug accumulated the chemistry of the Stigonematales, tremendous chemical diversity of—a rather small taxonomic subset of cyanobacteria, and most three decades of investigation, suggests that the order represents a unique repertoire of bioactive notably the polyphyletic genus, Lyngbya (Order Oscillatoriales), and limited number of other genera metabolites with relevance to both drug discovery and environmental health
Summary
Cyanobacteria are ubiquitous in the environment, but arguably best recognized as the conspicuous “blue-green algae” in freshwater and coastal habitats, and in association with eutrophication and episodic “harmful algal blooms” (HABs). An drug accumulated the chemistry of the Stigonematales, tremendous chemical diversity of—a rather small taxonomic subset of cyanobacteria, and most three decades of investigation, suggests that the order represents a unique repertoire of bioactive notably the polyphyletic genus, Lyngbya (Order Oscillatoriales), and limited number of other genera metabolites with relevance to both drug discovery and environmental health. To-date, only six genera representing only three (of the eight described) families of the order, namely Fischerellaceae (Fischerella, Westelliopsis), Mastigocladaceae (Hapalosiphon, Westiella, Mastigocladus) and Stigonemataceae (Stigonema), have been studied with respect to bioactive metabolites This pursuit has been inherently hindered by inabilities to culture representative species of other taxa, as well as lack of clear links to either toxicity or drug potential which might, otherwise, fuel research in this regard. The relevant toxic metabolites, in this case, remain to be identified
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