Senecio isatideus

Interestingly, the first biosynthetic experiments with [3H]linolenic add and the terrestrial plant Senecio isatideus (Asteraceae) as a model system for the biosynthesis of algal pheromones were unsuccessful. If, however, labeled dodeca-3,6,9-trienoic add is administered, a rapid transformation into ectocarpene takes place (36). Nevertheless, the C12 add ultimately derives from linolenic acid via three /3-oxidations, since labeled tetradeca-5,8,11-trienoic acid, which requires only one /3-oxidation, is converted into labeled ectocarpene albeit with very low effidency (37). 

Pyrrolizidine Alkaloids.—Retronecine (23), the most common base portion found in the pyrrolizidine alkaloids, has been shown to derive from two molecules of ornithine (1) via putrescine (3) by the use of 14C-labelled precursors19 (cf. Vol. 10, p. 13). Unequivocal evidence on the manner of incorporation of putrescine comes from experiments in Senecio isatideus with 13C-labelled samples of putrescine.20... 

Isatinecine, CsHwNOs, isolated as one of the hydrolysis products of isatidine (from Senecio isatideus) by Blackie (1), apparently differs from the necines of C8H13NO2 constitution because there is evidence that it is not a pyrrolizidine type base (22). Isatinecine has two carbon-carbon double bonds since de Waal (6, 20) found that hydrogenation over platinum... 

Isatidine was obtained from Senecio isatideus in 1.3% yield, along with retrorsine from Senecio retrorsus in 0.3% yield from Senecio sceleratiis in 0.05% yield. Compared with the other Senecio alkaloids, isatidine is unusual in its possession of a peroxygen atom which is easily removed by cat-... 

Retrorsine was extracted from the sources indicated in the following yields Senecio reirorsus, 1.3% Senecio isatideus, 0.15% Senecio glaberri-mus, 0.027% Senecio venoms, 0.01%. 

Another triquinane hydrocarbon of natural origin referred to as (-)-isocomene merits special attention it is a constituent of Isocoma wrigthii (Asteraceae) growing in the soufli east of die USA, better known there as rayless golden rod, and is highly toxic for cattle and sheep. It also occurs with the synonym berkheyaradulene in south African Asteraceae, such as in the roots of Berkheya and parts of Senecio isatideus. 

Figure 14.7 Biosynthesis of ectocarpene and homo-ectocarpene in Senecio isatideus (S. /).

The biosynthesis of ectocarpene in higher plants and brown algae therefore follows different pathways. In Senecio isatideus, the degradation of icosanoids by P-oxidation occurs prior to the formation of ectocarpene, but does not occur at all in Ectocarpus siliculosus. 

Boland, W. and Mertes, K. (1985) Biosynthesis of algal pheromones. A model study with the composite Senecio isatideus. Fur. J. Biochem., 147, 83-91. 

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