The Sea as a Potential Source

The oceans cover more than 70% of the earth s surface, which represents over 95% of the biosphere. The oceans are therefore an unexplored area of opportunity for the discovery of pharmacologically active compounds. Although it has been one of man s principal sources of food for thousands of years, the sea was not considered as a supply of biologically active substances until forty years ago. In the last two decades, the search for marine-derived natural products has been extended to all oceans of the world. The enormous potential of the sea as a source of energy, food and chemicals has led to its being the subject of intense research. The results of this search had been reported in numerous reviews [1-8]... 

Purine nucleosides are formed when a dilute solution of a purine, together with ribose or deoxyribose and MgClj is evaporated to dryness and heated at 100° C (Fuller et al., 1972). Yields of several percent of the a- and j3-isomers of adenosine, guanosine and xeinthosine, and about 10% of a- and j3-inosine are obtained. Interestingly, a mixture of the salts present in sea water produces even higher yields (15% of inosines). The simplicity of this reaction makes it attractive as a potential source of nucleosides. Unfortunately, it has not been possible to synthesize the pyrimidine nucleosides in this manner and there is as yet no satisfactory synthesis of these compounds. 

Nitrous oxide (N2O) is a potent greenhouse gas that has also been implicated in stratospheric ozone depletion. The atmospheric inventory of N2O is presently increasing, so there is a renewed interest in the marine ecosystem as a potential source of N2O. Nitrous oxide is a trace gas in sea water, with typical concentrations ranging from 5 to 50 nmol... 

Metabolites from cyanobacteria are generally of amino acid or polyketide origin and frequently show potent biological activity. The series of dolastatin metabolites, exemplified by dolastatin-10 (Structure 2.18), are linear peptides which show potent cytotoxic activity and are of clinical interest as anti-tumour agents. Originally isolated in very low yield from the Indian Ocean sea hare Dolabella auricularia, dolastatins are now known to be cyanobacterial products.43,44 The discovery of a microbial source for these pharmaceutically important compounds will facilitate study of their biosynthesis and could potentially lead to the production of structural analogues by provision of modified biosynthetic precursors to the cultivar. As discussed below and in Section VI, toxic secondary metabolites from cyanobacteria have often been implicated in the chemical defenses of sea hares.45"17... 

A decade later, the Black Sea ecosystem continues to be threatened by different chemical pollutants, mainly by nutrients that enter the Black Sea through rivers from land based sources. The Danube River accounts for about a half of the nutrient input to the Black Sea. As a result eutrophication occurs over wide areas of the Black Sea, in particular, in its northwestern part. Inputs of microbiological contaminants with insufficiently treated sewage result in a potential threat to public health as tourism continues to develop in the coastal zone. Satellite SAR imagery and related statistics of oil spills show... 

Certain individuals on Guam and other South Sea Islands exhibit an increased incidence of amyotrophic lateral sclerosis (ALS), parkinsonism and dementia. The absence of inheritable or transmissible factors in this syndrome led to a search for environmental causes and the identification of the false sago palm Cycas circinalis) as a likely source of the causative agent. This plant contains a number of potential neurotoxins including -N-methylamino-L-alanine (BMAA), an agent with weak excitotoxic properties (Spencer et al., 1990). 

Although zinc compounds provide an effective HjS treatment, the major disadvantage of using such scavengers is the potential environmental impact. Zinc is a conservative, heavy-metal pollutant that does not break down through time. The fate of the zinc—either as the sulfide or in its unreacted form will be to remain with the drill cuttings that are separated by the solids control equipment or to remain in the residual liquid mud. Both of these waste streams may be destined for disposal in the sea or on land. In both cases, the presence of zinc represents a potential source of serious contamination. 

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