Algal toxin from mussels synthesized
ETH Zurich chemists have synthesized an algal toxin that accumulates in mussels. This may help develop a method to detect the toxin in these molluscs before they are served up for human consumption.
Stomach upsets often occur after eating seafood and fish. Mussels are regarded as particularly “dangerous”, not only because they may have been out of the sea for a long time before they reach the plate, but also because these molluscs feed on plankton which they filter from the water. Some of the organisms that comprise plankton, mainly algae, produce toxins that eventually accumulate in the mussels – and poison whoever eats them.
Unexplored substance synthesised
A team led by chemistry professor Erick M. Carreira in the Organic Chemistry Laboratory has now carried out the first ever complete laboratory synthesis of a natural product from the chlorosulpholipids class and hence confirmed its structure. The researchers have just published their results in “Nature”.
The compound prepared in the laboratory has shown to have cytotoxic properties and could be partly responsible for food poisoning caused by mussels. In nature, it only occurs in minute amounts as a constituent of the membrane of the organisms from which it was isolated. The chlorosulpholipid being studied probably originates from a dinoflagellate, a tiny algal species. However, the role played by the substance as a membrane component is unresolved, especially since the amounts initially isolated were insufficient for detailed scientific studies.
Although chlorosulpholipids have been known since the sixties, the lipid that has just been synthesised was first isolated in the nineties from the mussel Mytilus galloprovincialis which is found in the Adriatic Sea. Christian Nilewski and Roger W. Geisser, chemists in Carreira’s laboratory, developed ground-breaking methodologies and strategies to synthesise this and related structures.
The way is open for toxicological studies
Thanks to their synthesis skills, the ETH Zurich researchers can now prepare larger amounts of the substance. This opens up new opportunities for biochemical, toxicological and medical studies. Carreira explains that, “The molecule we have synthesised may also help develop analytical methods which enable the toxin to be detected in mussels before they are sold to a restaurant.” The ETH Zurich chemists’ success also makes work easier for food technologists. Until now, they have used mice to check the level of algal toxins in mussels. In spite of these tests, and the rule of thumb that mussels should not be eaten in the spring and summer months, many cases of poisoning occur every year. Mussel poisonings in particular are often severe, with symptoms extending from tingling lips to paralysis of the respiratory muscles, potentially leading to death.
Many questions remain unanswered
This first synthesis of a representative of the chlorosulpholipids now offers an opportunity to decipher more secrets about “mussel toxins”. For example, little is known about the ecological function and potential hazards of these substances. Thanks to the laboratory synthesis, these substances will probably soon cause fewer headaches for scientists – and seafood lovers.
Nilewski C, Geisser RW, Carreira EM. Total synthesis of a chlorosulpholipid cytotoxin associated with seafood poisoning. Nature 457, 573 - 576 (29 Jan 2009), doi: 10.1038/nature07734