Characterization of tamulamides A and B, polyethers isolated from the marine dinoflagellate Karenia brevis

Abstract

Florida red tides occur as the result of blooms of the marine dinoflagellate Karenia brevis. K. brevis is known to produce several families of fused polyether ladder compounds. The most notable compounds are the brevetoxins, potent neurotoxins that activate mammalian sodium channels. Additional fused polyether ladder compounds produced by K. brevis include brevenal, brevisin, and hemibrevetoxin B, all with varying affinities for the same binding site on voltage-sensitive sodium channels. The structure elucidation and biological activity of two additional fused polyether ladder compounds containing seven fused ether rings will be described in this paper. Tamulamide A (MW = 638.30) and tamulamide B (MW = 624.29) were isolated from K. brevis cultures, and their structures elucidated using a combination of NMR spectroscopy and high-resolution mass spectrometry. Tamulamides A and B were both found to compete with tritiated brevetoxin-3 ([(3)H]-PbTx-3) for its binding site on rat brain synaptosomes. However, unlike the brevetoxins, tamulamides A and B showed no toxicity to fish at doses up to 200 nM and did not cause significant bronchoconstriction in sheep pulmonary assays.

Figure 1

TOCSY and HMBC correlations for A. TamA and B. TamB. Bold lines indicate spin systems as determined by ¹H-¹H correlations for TOCSY experiments. Arrows indicate ¹H-¹³C correlations for HMBC experiments.

Figure 2

¹H-¹H ROESY correlations for TamA and TamB. Double headed arrows indicate important ROESY correlations for TamA and TamB as determined by NMR. Single headed arrow indicates an additional ROESY correlation for TamB.

Figure 3

Inhibition of [³H]-PbTx-3 binding to rat brain synaptosomes by TamA and TamB. Each data point represents the mean ± S.E.M. of at least 3 experiments. * indicates two experiments at the indicated concentration due to lack of material.