Isolation and Determination of Structure and Biological Activity of a Toxin Produced by the Dinoflagellate, Alexandrium monilatum

Michelle H. Hsia^1,3, Steve Morton^1,2, and Peter  D.R. Moeller^1,3

¹ Marine Biomedicine and Environmental Sciences Center, Medical University of South Carolina, Charleston, SC

² Marine Biotoxins, National Ocean Service, Charleston, SC

³ Toxin Chemistry, National Ocean Service, Charleston, SC

The chain-forming dinoflagellate Alexandrium monilatum has been reported to be associated with widespread discolored water and increased fish mortality in the Mississippi Sound and off the eastern and western coasts of Florida.  Previous studies over the last 70 years have determined that A. monilatum produces a harmful substance(s) that is predominantly contained in the cell mass as exhibited by apparent increased toxicity when the organism cytolyses.  The current research in our lab corroborated earlier research demonstrating that A. monilatum produces a lipophilic toxin, unlike its Alexandrium relatives noted for their production of saxitoxin-like toxins.  Using sophisticated chemical, chromatographic, and analytical techniques, we have successfully purified and identified the molecular structure of the toxin produced by A. monilatum.  We utilized a 500MHz NMR to carry out a number of experiments (i.e. ¹H, ¹³C, COSY, HSQC, HMBC) to unambiguously determine the molecular structure of the toxin.  In addition, we performed mass analysis of the toxin using ESI-MS, MALDI-TOF MS, and Q-TOF mass spectral techniques.  The toxin is representative of a polyether macrolide with an empirical formula of C₄₃H₆₀O₁₂.  This toxic compound is shown to be identical to a toxin identified as goniodomin A, which is produced by a Japanese tide-pool Alexandrium species.