Red tides

Red rubber Red Rubber 107 Reds 1 Red seaweed Red tide algae Red TR [3165-93-3]... 

The striking constitution of brevetoxin B, unprecedented at the time of its discovery in 1981, presents a formidable challenge to organic synthesis. The unique and fascinating molecular architecture of brevetoxin B (1), its association with the red tide catastrophes, its potent biological activity, and the prospects for expanding the arsenal of synthetic methods all contributed in roughly equal measure to our decision to pursue a total synthesis of 1. This chapter addresses the efforts that culminated in the total synthesis of brevetoxin B (1 ).6... 

This lithiated epoxysulfone cyclisation strategy has been iteratively applied in the total synthesis of hemibrevitoxin B, a polycyclic ether marine toxin from the red tide organism Gymnodinium breve (Scheme 5.41) [64]. 

The biosynthesis of two major classes of red tide toxins, saxitoxin analogs and brevetoxins, have been studied. It was shown that saxitoxin is biosynthesized from arginine, acetate, and methionine methyl group. Brevetoxins were shown to be unique polyketides, which are probably biosynthesized from dicarboxylic acids. Some details of the biosynthetic mechanism have been elucidated. 

The toxicological consequences of P. brevis red tides are mass mortality of fishes exposed to the red tide toxic shellfish which, if consumed, result in human neurotoxic shellfish poisoning and an irritating aerosol which results from contact with P. brevis cell particles entrapped in seaspray. In all cases, the threshhold levels for intoxication are in the picomolar to nanomolar concentration ranges, implying a specific locus or loci of action for brevetoxins (reviewed in 6). 

The possibility of managing a bloom of Ptychodiscus brevis has been considered for many years, and various limitations have been noted to the use of chemical control (3) or the use of control by some organisms (7). Chiefly, the problems are two-fold the volume to be treated and the limitations of the control agent. For example, a red tide may cover hundreds of square miles, it will be present in patches, and may be unevenly distributed through the water column. 

One response may be that it is possible to manage the red tide at the source of the bloom (8) or that there is no need to manage a red tide over vast areas, merely in localized ones that are of special interest. The point is moot until a suitable control agent is available. A considerable number of chemicals have been reviewed for possible red tide control substances, (9), and in retrospect this type of research is subject to ultimate failure because the first criterion of a successful control agent (chemical or biological) has not been considered. 

An alga, isolated from a red tide outbreak area, produced chloroform-soluble material capable of causing lysis of . brevis. 

The results presented here indicate the existence of environmentally significant allelopathic substance or substances that affect a red tide organism in laboratory studies. It would be difficult to imagine that such substances do not have some impact in the natural environment, particularly in view of the observed (26) distribution of aponin vis-a-vis the presence of "seed beds" of red tide (8). 

Scheme 2 Polyether toxins form red tide dinoflagellates...

Surprisingly few studies have been performed with purified toxins. When added externally to the water, toxins of various origins were tested on the cope-pod Tigriopus californicus. The protein phosphatase inhibitor okadaic acid (17) from red tide dinoflagellates [22] and the neuronal depolarizing agent do-moic acid (10) from diatoms [40, 41] had different effects on the herbivores (Scheme 3). Micromolar concentrations of okadaic acid (17) acted both as toxin... 

Paralytic neurotoxins that bind to sodium channels of nerve and muscle cells causing muscle contractions. They are obtained from the dinoflagellate that causes "red-tide" (Gymnodinium breve). Toxins are typically light tan crystalline solids. They are insoluble in water and very unstable. 

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