FIGURE 8 Gas chromatographic separation of the volatiles of D. diemensis egg extracts (47). Conditions: fused silica column OV 1 (10 m x 0.32 mm); 50°C isotherm for 2 min, then at 10°C/min to 250°C; injection port: 250°C; detector: Finnigan ion trap, ITD 800; transfer line at 270°C; electron impact (70 eV); scan range, 35-250 Da/sec. For identity of numbered compounds refer to Figure 9.

(Figure 1), ¹H NMR studies show that at ambient temperature, the monocyclic 7-methylcyclooctatriene is present as the only isomer (no evidence for an equilibrium with a bicyclic cyclohexadiene).

The degree and extent of the abiotic degradation of the pheromones becomes immediately obvious when samples from algae releasing cyclohepta-1,4-dienes (such as dictyotene or ectocarpene) are collected. For example, volatiles collected from cultures of fertile gynogametophytes of Dictyota diemensis exhibit, besides dictyotene, a complex pattern of oxygenated compounds, as shown in Figure 8 (47). Since the concentrations of the oxygenated products are even lower than that of the genuine pheromone, the enrichments from natural sources can not be used for an exhaustive structure elucidation.

However, the pattern of Figure 8 can be perfectly mimicked by a chemical model system with dictyotene as the substrate and iodosylben-