Algal Toxin Breaks Record

For three months in 1998, a red tide blanketed parts of the southern coast of New Zealand’s North Island. A new algae species, Karenia brevisulcata, in the bloom spewed toxins that killed most fish in Wellington Harbor and caused respiratory problems in more than 500 people nearby. Now chemists have determined the structure of one of the toxins and noted that it has the longest contiguous polycyclic ether structure ever observed in an algal toxin (J. Am. Chem. Soc., DOI: 10.1021/ja212116q).

Scientists had previously isolated groups of toxins from this species, but the large size of many of the molecules made complete structural determination difficult. Masayuki Satake, of the University of Tokyo, and his colleagues have isolated and characterized one of the most prevalent toxins, brevisulcenal-F.

The team isolated the compound by passing extracts of the algae through several rounds of chromatography, picking only the fractions that killed mouse leukemia cells. They then determined the molecule’s structure using high-field two-dimensional nuclear magnetic resonance spectroscopy to resolve the many signals that overlap because of the molecule’s size. To confirm their NMR data, the chemists also used tandem mass spectroscopy.

Brevisulcenal-F contains 17 contiguous ether rings, making it the longest polycyclic ether system of any marine algal toxin. The previous record holder was gymnocin-B, with 15 fused rings. Another string of five connected ether rings attaches to the brevisulcenal-F core by a flexible carbon string. An aldehyde dangles from the other end of the core.

The pendant aldehyde and ether rings are common in marine algal toxins. Comparing the structure of brevisulcenal-F to that of other known toxins, such as gymnocins and brevetoxins, will help scientists determine how these common features influence each toxin’s potency, Satake says.