Natural marine products secondary metabolites

Prior to the discussion of the misassigned marine-derived molecules, it is instructive to consider the diversity of marine natural products. The structures collected in Figure 3 are several marine natural products either revised or possessing incomplete stereochemistry and represent each biosynthetic class. This short list of compounds demonstrates that marine-derived secondary metabolites have characteristic structural diversity when compared with terrestrial-derived molecules. Unique carbon skeletons and functional groups are present in the structures of suvanine, ecteinascidine 759B, spirastrellolide and yendolipin ... 

The widespread nature of secondary metabolite production and the preservation of their multigenic biosynthetic pathways in nature indicate that secondary metabolites serve survival functions in organisms that produce them. There are a multiplicity of such functions, some dependent on antibiotic activity and others independent of such activity. Indeed in the latter case, the molecule may possess antibiotic activity but may be employed by a producing microorganism for an entirely different purpose. Some useful reviews on secondary metabolism have appeared in recent years [23,47 -49]. Examples of marine secondary metabolites playing a role in marine ecology have been given by Jensen and Fenical [50]. 

The held of marine natural products chemistry, which encompasses the study of the chemical structures and biological activities of secondary metabolites produced by marine plants, animals, and microorganisms, began in earnest in the early 1960s. " This is in stark contrast to the study of terrestrial plant natural... 

The underlying assumption driving marine natural products chemistry research is that secondary metabolites produced by marine plants, animals, and microorganisms will be substantially different from those found in traditional terrestrial sources simply because marine life forms are very different from terrestrial life forms and the habitats which they occupy present very different physiological and ecological challenges. The expectation is that marine organisms will utilize completely unique biosynthetic pathways or exploit unique variations on well established pathways. The marine natural products chemistry research conducted to date has provided many examples that support these expectations. 

Early natural product research with marine mollusks supported a conclusion that all secondary metabolites of mollusks are diet-derived, which proved to be premature. In fact, the biosynthetic capability of some marine mollusks covers a wide spectrum of chemical classes and substances. Much of this recent insight has resulted from work in the laboratories of the authors of Chapter 3. 

While secondary metabolites of plants and animals have been the subject of many chemical investigations, their associations and roles in their host organism are at times controversial this is particularly so, when insufficient observations exist. Nevertheless, natural products provide fruitful areas of research [69]. There is little doubt that chemical defense against predators is an important aspect of survival. In the marine environment, early observations of nudi-branch- sponge relationships were reported and those relating to isocyano compounds are summarized in Table 6. 

The studies on the biosynthetic origin of secondary metabolites in marine molluscs are reviewed. Although the majority of natural products found in marine molluscs appears to have a dietary origin, de novo biosynthetic ability towards particular classes of compounds has been demonstrated. Marine molluscs are also able to modify metabolites sequestered from their specific prey. 

Throughout this chapter a major emphasis is given to recent work, since the biosynthesis of molluscan secondary metabolites has been partly covered in previous reviews [8, 9] devoted to the entire field of the biosynthetic studies on marine natural products. 

Chlorophyta or green algae comprise one of the major groups of algae and include several exclusively marine orders and genera from tropical regions. Natural products chemistry research has identified more than 300 secondary metabolites from Chlorophyta, with most being sesquiterpenoid and diterpenoid compounds... 

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