Pyrrolizidine plant sources

Extraction of the pyrrolizidine alkaloids and their N-oxides from plant sources is a critical first step in LG-MS analysis. Some methods of extraction already described (Section 13.2) consist simply of treatment with aqueous methanol and, following microfiltration (0.45 p.m), immediate LC-MS analysis with no further treatment. However, the aqueous methanol treatment will extract more than just the alkaloids. 

Smith, L.W., and C.C.J. Culvenor. 1981. Plant sources of hepato-toxic pyrrolizidine alkaloids. /. Nat. Prod. 44 129-152. 

Pyrrolizidine alkaloids are toxic for animals and possess importance as feeding deterrents (E 5.5.3). Certain insects, however, are able to store pyrrolizidine alkaloids, e.g., senecionine, ingested with the diet for the repellence of potential predators (E 5.1). Some kinds of butterflies hydrolyze pyrrolizidine alkaloids taken up from plant sources and transform the necine bases to pyrrolizidine aldehydes and ketones (Fig. 224) used as sex pheromones (E 4). 

Most pheromones are synthesized de novo in the animal body. Some, however, are taken up from plant sources and are used directly or in a modified form (cf. the pyrrolizidines secreted as sex pheromones from male Danaid butterflies and myrcene used as sex pheromone of Dehdroctonus brevicomis Table 66). In Creatonotos moths, pyrrolizidine alkaloids ingested by the larvae with the diet, in addition to their action as pheromone precursors, show hormone-like activity and control the morphogenesis of the scent organs. 

This compound exhibits the same relationship to (3-D-fructofuranose as 1-deoxy-nojirimcin does to D-glucopyranose. In 1979, a polyhydroxyindolizidine alkaloid was isolated from the poisonous fruit of Castanospermum australe, a handsome Australian indigenous tree, and coined castanospermine (8) after its source.28 A compound subsequently isolated from the seeds of this plant was the pyrrolizidine australine (9),29 also found in Alexa leiopetala,30 along with other compounds. These discoveries increasingly supported the hypothesis that imino sugars and their structural relatives might be a fairly common family of natural products, and their widespread... 

Plant species known to contain pyrrolizidine alkaloids have been listed by Smith and Culvenor.1 These sources are classified according to the toxicity of the alkaloids that are present. It is estimated that the potential number of these alkaloid-containing species is as high as 6000, or 3% of the world s flowering plants.2... 

Insects have evolved mechanisms to tolerate plant toxins. Such mechanisms enable them to use a plant as a food source that is avoided by other herbivores, and provides the herbivore with its own ecological niche.9 For example, insects may prevent accumulation of detrimental alkaloids in the hemolymph by efficient excretion. Larvae of Spodoptera littoralis (Lepidoptera, Noctuidae) feed freely on plants containing pyrrolizidine alkaloids that are rapidly excreted and only transiently detectable in the hemolymph. Even pyrrolizidine alkaloids directly injected into the hemolymph are efficiently excreted.48 The same has been observed... 

Males of the flea beetle Gabonia gabriela feed on withered Heliotropium plants. This may provide a source of pyrrolizidine alkaloids but the significance of this observation is not yet clear. ... 

Senecio vulgaris (Asteraceae) is a perennial plant that came to Japan in the Meiji Era (1868—1912) and spread as a naturalized plant aU over the country. In contrast, Senecio pierotii (Asteraceae) is a perennial plant that grows in the swamps of the mountains in Japan. Pyrrolizidine alkaloids, which possess a pyrrolizidine nucleus, were isolated from a number of Senecio plants, inclu-deing S. vulgaris and S. pierotti. These alkaloids are distributed in Senecio plants, and several other genera of plants in the Asteraceae, Boraginaceae, and Fabaceae. Because their principal source is Senecio plants, these pyrrolizidine alkaloids are also known as Senecio alkaloids. 

Pyrrolizidine alkaloids are a large and important group of about 250 alkaloids produced by approximately 6000 plant species belonging to 13 families. The most important plants belong to the famflies Boraginaceae, Asteraceae, Heliotropiaceae, Fabaceae and Rham-naceae. Pyrrolizidine alkaloids occur in relatively small amounts (0.1-1% of dry matter) as a complex mixture of more than ten different compounds. Important sources of alkaloids are some herbs and certain fodder plants. 

Outbreaks of pyrrolizidine poisonings in humans have occurred and have generally been associated with contaminated grain used for meal or bread. The pyrrolizidines have also been detected in comfrey teas (Roitman, 1981) commonly available at herbal medicine and health food stores. The possibility of the occurrence of pyrrolizidine residues in meat or milk of livestock consuming toxic plants exists, but no toxic responses in humans from this source has been reported (Peterson and Culvenor, 1983). 

---