TOTAL SYNTHESIS OF BREVETOXIN-A

Brevetoxin A is the most potent neurotoxin secreted by Gymnodinium bre ve Davis, a marine organism often associated with harmful algal blooms known as 'red tides'(1-3). The compound, whose mechanism of action in volves binding to and opening of sodium channels(4-7), is sufficiently toxic to kill fish at concentrations of nanogams per mi (refs 3, 4) a nd, after accumulation in filter-feeding shellfish, to poison human co nsumers. The precise pathway by which nature constructs brevetoxin A i s at present unknown(8,9), but strategies for its total synthesis have been contemplated for some time. The synthetic challenge posed by bre vetoxin A reflects the high complexity of its molecular structure: 10 oxygen atoms and a chain of 44 carbon atoms are woven into a polycycli c macromolecule that includes 10 rings (containing between 5 and 9 ato ms) and 22 stereogenic centres. Particularly challenging are the 7-, 8 - and 9-membered rings which allow the molecule to undergo slow confor mational changes and force a 90 degrees twist at one of its rings(1-6) . Here we describe the successful incorporation of methods that were s pecifically developed for the construction of these rings(10,11) into an overall strategy for the total synthesis of brevetoxin A in its nat urally occurring form. The convergent synthesis reported here renders this scarce neurotoxin synthetically available and, more importantly, allows the design and synthesis of analogues for further biochemical s tudies.