Assignment of the relative stereochemistry of the spirolides, macrocyclic toxins isolated from shellfish and from the cultured dinoflagellate Alexandrium ostenfeldii

The relative stereochemistry of 13-desmethyl spirolide C, except for one chiral center, has been determined from NMR data by means of ConGen, a molecular modeling method which applies high-temperature molecular dynamics under distance constraints generated from NOESY and ROESY data. The method shows this spirolide to have the same relative stereochemistry as pinnatoxins A and D in the region of their common structure. Applicability of the ConGen method to molecules of this type is further justified by demonstrating that it yields the correct relative stereochemistry of the pinnatoxins when used with constraints generated from published data. The relative stereochemistries of spirolides B and D are also determined by comparisons of their NMR data with 13-desmethyl spirolide C and further application of ConGen.