Max-Planck-Institut für Chemische Ökologie, Tatzendpromenade 1a, 07745 Jena, Germany.
The fresh water diatoms Gomphonema parvulum and Asterionella
formosa produce high amounts of linear and monocyclic C9- and C11-hydrocarbons,
previously identified as brown algal pheromones. Highly unsaturated eicosanoic acids like
20:5 (w
-3) and 20:4 (w
-6) have been shown as their biosynthetic precursors. Cleavage of an intermediate 9- or
12-hydroperoxy fatty acid, involves a hydroperoxide-lyase giving 9-oxo-nonadienoic acid
or 12-oxo-dodecatrienoic acid and the corresponding C11- or C9- hydrocarbon
1,2. This pathway was confirmed by incubation experiments under
18O2-atmosphere using (chirally) deuterated fatty acids
yielding the respective fragments with exceptional high degrees of labelling. The labelling
pattern in the resulting metabolites is consistent with the low enantiomeric excess found in
the natural products. Mechanistic and kinetic studies show, that the strong Michael acceptor
9-oxo-nonadienoic acid is produced in 1:1 stoichiometry with the C11-hydrocarbons. This
oxo-acid significantly reduces feeding by the herbivorous amphipod Ampithoe
longimana when added to artificial diets at naturally relevant concentrations (0.1% of
whet weight)3. We thus assume the lipoxygenase / hydroperoxide
lyase products to be important for algal chemical defense.
1Pohnert G., Boland W., Tetrahedron, 52 10073-10082 1996.
2Hombeck M., Pohnert G., Boland W, Chem. Commun. 243-244 1999.
3Schnitzler I., Pohnert, G., Hay, M., Boland, W., in preparation.