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The isolation and structural determination of new marine ladder-frame polyethers, brevisulcatic acids-1 (1) and -4 (2) are reported. Brevisulcatic acids were isolated from the dinoflagellate Karenia brevisulcata, which was identified as the causative species of a major red tide event in New Zealand in 1998. The ether ring composition and a β-hydroxy, γ-methylene valeric acid side chain of 1 and 2 are common, but 2 has a γ-lactone as the 5-membered A-ring while 1 is the seco acid analogue. Compound 2 has structural and bioactivity similarities to brevetoxin A.

A novel marine toxin, brevisulcenal-F (KBT-F, from karenia brevisulcata toxin) was isolated from the dinoflagellate Karenia brevisulcata. A red tide of K. brevisulcata in Wellington Harbour, New Zealand, in 1998 was extremely toxic to fish and marine invertebrates and also caused respiratory distress in harbor bystanders. An extract of K. brevisulcata showed potent mouse lethality and cytotoxicity, and laboratory cultures of K. brevisulcata produced a range of novel lipid-soluble toxins. A lipid soluble toxin, KBT-F, was isolated from bulk cultures by using various column chromatographies. Chemical investigations showed that KBT-F has the molecular formula C(107)H(160)O(38) and a complex polycyclic ether nature. NMR and MS/MS analyses revealed the complete structure for KBT-F, which is characterized by a ladder-frame polyether scaffold, a 2-methylbut-2-enal terminus, and an unusual substituted dihydrofuran at the other terminus. The main section of the molecule has 17 contiguous 6- and 7-membered ether rings. The LD(50) (mouse i.p.) for KBT-F was 0.032 mg/kg.

Yessotoxins from a large-scale culture (226 L) of Protoceratium reticulatum strain CAWD129 were harvested by filtration followed by solid-phase extraction. The extract was purified by column chromatography over basic alumina and reverse-phase flash chromatography to afford pure yessotoxin (193 mg). Isolation of yessotoxin was greatly facilitated by selection of a strain which did not produce analogues that interfered with yessotoxin isolation. In addition to yessotoxin, numerous minor yessotoxins were detected by LC-MS in other fractions. From one of these, an early eluting minor analogue with the same molecular weight as yessotoxin and a similar mass spectrometric fragmentation pattern was isolated. This analogue was identified by NMR and mass spectrometry as a novel yessotoxin analogue containing a furan ring in the side chain. This finding reveals biosynthetic flexibility of the yessotoxin pathway in P. reticulatum and confirms earlier findings of production of many minor yessotoxin analogues by this alga. Production of these analogues appeared to be a constitutive trait of P. reticulatum CAWD129.

Pectenotoxins (PTXs) accumulate in shellfish feeding on dinoflagellates of the genus Dinophysis, so that humans can be exposed to these toxins through shellfish consumption. Some PTXs are toxic to experimental animals, whereas others are of much lower toxicity. Pectenotoxin-2, the most abundant PTX from most Dinophysis spp., is rapidly metabolized by most shellfish to a mixture of pectenotoxin-2 seco acid (2) and 7-epi-pectenotoxin-2 seco acid (1). A mixture of 1 and 2 was produced during purification of an extract from in vitro enzymatic hydrolysis of pectenotoxin-2. These were separated by preparative HPLC, and the structure of 1 was confirmed by one- and two-dimensional 1H and 13C NMR spectroscopy and LC-MS3 analyses. No toxic changes were recorded in mice injected intraperitoneally with 1 or 2 at a dose of 5000 microg/kg. PTX seco acids are therefore unlikely to be of consequence to human consumers at the concentrations found in contaminated shellfish.

A new pectenotoxin, which has been named pectenotoxin-11 (PTX11), was isolated from the dinoflagellate Dinophysis acuta collected from the west coast of New Zealand. The structure of PTX11 was determined as 34S-hydroxypectenotoxin-2 by tandem mass spectrometry and UV and NMR spectroscopy. PTX11 appears to be only the third pectenotoxin identified as a natural biosynthetic product from algae after pectenotoxin-2 and pectenotoxin-12. The LD50 of PTX11 determined by mouse intraperitoneal injection was 244 microg/kg. The LD(min) of PTX11 in these experiments was 250 microg/kg. No signs of toxicity were recorded in mice following an oral dose of PTX11 at 5000 microg/kg. No diarrhea was observed in any of the animals administered with the test substance by either route of administration. Unlike pectenotoxin-2 (PTX2), PTX11 was not readily hydrolyzed to its corresponding seco acid by enzymes from homogenized green-lipped mussel (Perna canaliculus) hepatopancreas.