Organobromine Compound - Organobromine Compounds in Nature

Organobromine Compounds in Nature

Organobromine compounds are the most common organohalides in nature. Even though the concentration of bromide is only 0.3% of that for chloride in sea water, organobromine compounds are more prevalent in marine organisms than organochlorine derivatives. Their abundance reflects the easy oxidation of bromide to the equivalent of Br+, a potent electrophile. The enzyme bromoperoxidase catalyzes this reaction. The oceans are estimated to release 1–2 million tons of bromoform and 56,000 tons of bromomethane annually. Red algae, such as the edible Asparagopsis taxiformis, eaten in Hawaii as "limu kohu", concentrate organobromine and organoiodine compounds in "vesicle cells"; 95% of the essential volatile oil of Asparagopsis, prepared by drying the seaweed in a vacuum and condensing using dry ice, is organohalogen compounds, of which bromoform comprises 80% by weight. Bromoform, produced by several algae, is a known toxin, though the small amounts present in edible algae do not appear to pose human harm. Some of these organobromine compounds are employed in a form of interspecies "chemical warfare." 5-Bromouracil and 3-Bromo-tyrosine have been identified in human white blood cells as products of myeloperoxidase-induced halogenation on invading pathogens.

In addition to conventional brominated natural products, a variety of organobromine compounds result from the biodegradation of fire-retardants. Metabolites include methoxylated and hydroxylated aryl bromides as well as brominated dioxin derivatives. Such compounds are considered persistent organic pollutants and have been found in mammals.