Biosynthetic origins of the cyclic imine toxin 13-desmethyl spirolide C were determined by supplementingcultures of the toxigenic dinoflagellate
Alexandrium ostenfeldii with stable isotope-labeled precursors[1,2-
13C
2]acetate, [1-
13C]acetate, [2-
13CD
3]acetate, and [1,2-
13C
2,
15N]glycine and measuring the incorporation patterns by
13C NMR spectroscopy. Despite partial scrambling of the acetate labels, the results showthat most carbons of the macrocycle are polyketide-derived and that glycine is incorporated as an intactunit into the cyclic imine moiety. This work represents the first conclusive evidence that such cyclicimine toxins are polyketides and provides support for biosynthetic pathways previously defined for otherpolyether dinoflagellate toxins.
