Fig. 1.

Chemical structures of the spirolides (Left) and gymnodimines (Right). The seven- and six-membered cyclic imines common to the phycotoxins are highlighted with a gray background, and the chemical groups specific to each are boxed. Locations of group substitutions that differ among the various spirolides and gymnodimines are indicated. SPX (13-desmethyl spirolide C): R₁ = CH₃, R₂ = H, R₃ = CH₃. GYM (gymnodimine A): R₁ = CH₃. Substitutions found in SPX and GYM congeners are described in the SI Appendix.