• algae;
  • dinoflagellate;
  • Karenia;
  • lipid;
  • sterol


Karenia brevis is a harmful marine dinoflagellate that forms yearly blooms in the Gulf of Mexico. Under normal growth conditions, K. brevis forms two predominant sterols (24R)-4α-methyl-5α-ergosta-8(14),22-dien-3β-ol (gymnodinosterol) and its 27-nor isomer (brevesterol). At the current time, there are no published studies concerning the biosynthesis of these two sterols. We have therefore undertaken experiments in which K. brevis was exposed to the fungicide fenpropidine, an inhibitor of the Δ14-reductase and the Δ8[RIGHTWARDS ARROW]7-isomerase that operate in sterol biosynthesis in both fungal and plant systems. Such exposure to fenpropidine has produced two, tri-unsaturated intermediates. The identifications of these two K. brevis sterol biosynthesis intermediates, via gas chromatography/mass spectrometry and nuclear magnetic resonance spectroscopy techniques, were 4α-methyl-5α-ergosta-8,14,22-trien-3β-ol and 5α-ergosta-8,14,22-trien-3β-ol.