Graduate Thesis Or Dissertation

Marine algal secondary metabolites of unique structure and biomedicinal or agrichemical potential

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  • This thesis describes investigations of marine algal secondary metabolites, with particular interest in their biomedical and agrichemical potential. Invaluable in such pursuits have been the access and application of advanced spectroscopic techniques, such as NMR, and the ability to assess the biological activity of the algal samples in a variety of diverse protocols, through in-house evaluation and industrial collaborations. As an in-house bioassay, a survey of algal extracts for molluscicidal activity has led to the isolation of the previously reported chondrocole C (Portieria hornemanni), tanikolide (Lyngbya majuscula), and debromoaplysiatoxin (L majuscula). Debromoaplysiatoxin is 100 times more potent than niclosamide, the commercially utilized molluscicide. Such activity may make debromoaplysiatoxin an attractive agent for molluscan biological control to prevent the spread of schistosomiasis in artificial waterways such as irrigation channels and rice paddies. The isolation of chondrocole C led to further chemical investigations of P. hornemanni. A total of six related polyhalogenated monoterpenes were isolated from this collection. While four of these compounds were previously reported, taviochtodene represents the newest member of this class of secondary metabolites. Previously, this alga has yielded compounds with great potential anticancer utility, but naturally and synthetically elusive. The discovery of this class of chemistry potentially locates new geographic territory to search for such anticancer metabolites. While there has been little reported biological activity attributed to the malyngamides, they form the most prevalent class of secondary metabolites isolated from Lyngbya majuscula. To this list we have added malyngamides L, Q, and R. Of particular note, malyngamides Q and R were the first malyngamides to have been reported with altered stereochemistry at the vinyl chloride carbon. Subsequently, and in part stimulated by this finding, this alternate stereochemistry has been defined for some newly reported malyngamides. Also from L majuscula, tortugin and lyngbyabellin B were isolated as toxic cyclic depsipeptides. Both of these compounds displayed relatively potent biological activity (brine shrimp and antifungal). Each possessing particular structural motifs previously seen in invertebrate secondary metabolites, they lend further evidence for cyanobacteria as the producer of many of the polyhalogenated compounds often attributed to de novo invertebrate biosynthesis.
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