Metabolite halogenated

Figure 4 Halogenated terpenoid and polyketide metabolites isolated from red algae in the genera Laureucia and Plocamium...

Caccamese, S., R. Azzolina, R. M. Toscano and K. L. Rinehart, Jr. 1981. Variations in the halogenated metabolites of Laurencia obtusa from eastern Sicily. Biochem. Syst. Ecol. 9 241-246. 

Masuda, M., Abe, T., Sato, S., Suzuki, T. and Suzuki, M. 1997a. Diversity of halogenated secondary metabolites in the red alga Laurencia nipponica (Rhodomelaceae, Ceramales) J. Phycol. 33 196-208. 

San-Martin, A. and Rovirosa, J. 1986. Variations in the halogenated monoterpene metabolites of Plocamium cartilagineum of the Chilean coast. Biochem. Syst. Ecol. 14 459-461. 

Finally, the presence in human post-mortem brain tissue of the active metabolite of diazepam, desmethyldiazepam, raised some curiosity and frank alarm (Sangameswaran et al. 1986). At the time of its discovery in the brain it was thought that there was no enzyme system capable of producing such halogenated compounds and that its presence in the brain reflected dietary intake from an environment contaminated by overuse of its parent compound. However, its discovery in stored brain tissue which had been obtained before the synthesis of the benzodiazepines allayed these fears. It is now thought possible that some benzodiazepines, including desmethyldiazepam, occur naturally and that they are taken in as part of a normal diet (Table 19.5). 

Aerobic degradation of chlorinated arene hydrocarbons, including the important group PCBs, and chlorobenzoates that are produced from them as metabolites, is generally initiated by dihy-droxylation of the rings to dihydrodiols followed by dehydrogenation to catechols. Halide may be lost simultaneously and for 2-halogenated benzoates, both halide and carboxyl. Salient aspects are summarized, and attention drawn to selected aspects of enzyme inhibition. 

Scheme 11 Halogenated aromatic metabolites involved in the chemical defense of the polychaete Capitella sp.

Marine organisms have incorporated halogen atoms into the structures of many of their metabolites ... 

The pyrrole ring is widely distributed in nature. It occurs in both terrestrial and marine plants and animals [1-3]. Examples of simple pyrroles include the Pseudomonas metabolite pyrrolnitrin, a recently discovered seabird hexahalogenated bipyrrole [4], and an ant trail pheromone. An illustration of the abundant complex natural pyrroles is konbu acidin A, a sponge metabolite that inhibits cyclin-dependent kinase 4. The enormous reactivity of pyrrole in electrophilic substitution reactions explains the occurrence of more than 100 naturally occurring halogenated pyrroles [2, 3]. 

While common biosynthetic pathways may provide the framework for the various classes of secondary metabolites, their functionality is imparted by specialized tailoring enzymes that are often unique to natural products (Walsh 2004 Hertweck et al. 2007). Whether it is the addition of alcohol groups, halogenation (Gribble 1998), oxidation, reduction, stereochemical manipulation, or cyclization, it is often these functionalities that make secondary metabolites unique and bioactive. 

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