Asteraceae , pyrrolizidine

Defensive Compounds. The aposematically coloured Chauliognathusfallax which feed on Senecio brasiliensis (Asteraceae) sequester the four pyrrolizidine alkaloids senecionine (100 main compound), integerrimine (101 main compound), retrorsine 102, and usaramine 103 [203] (Scheme 11). Other Chauliognathus-species may contain either precoccinelline 104 and related alkaloids (C. pul-chelus) or Z-dihydromatricaria acid 105 (C. pennsylvanicus). 

Pelser, P. B., Vos de, H., Theuring, C Beuerle, T., Vrieling, K. and Hartmann, T. 2005. Erequent gain and loss of pyrrolizidine alkaloids in the evolution of Senecio section Jacobaea (Asteraceae). Phytochemistry, 66 1285-1295. 

Pyrrolizidine alkaloids have a wide distribution, but are characteristic of certain genera of the Boraginaceae (e.g. Heliotropium, Cynoglossum, and Symphytum), the Compositae/Asteraceae (e.g. Senecio) and the Leguminosae/Fabaceae (e.g. Crotalaria). The pyrrolizidine bases rarely occur in the free form, but are generally found as esters with rare mono- or di-basic acids, the necic acids. Thus, senecionine (Figure 6.18) from Senecio species is a diester of retronecine with senecic acid. Inspection of the ten-carbon skeleton... 

PAs are found widely in the families Asteraceae, Boraginaceae, Fabaceae, and Apocynaceae. About 360 diverse structures have been characterized,23 and these widespread alkaloids are produced by at least 3% of all flowering plants. It is remarkable that one group of animals-the insects-have broken through the formidable alkaloidal defenses represented by the highly toxic pyrrolizidine alkaloids. This evolutionary adaptation has provided a large resource for these insects that is not available to PA-intolerant species, which constitute most of the herbivores. 

The best-studied group of acquired alkaloids are the pyrrolizidines, which are produced by plants, especially in the families Asteraceae and Boraginaceae (502). Some arctiid larvae of Tyria Jacobaea, Cycnia men-dica, Amphicallia bellafrix, Arginia cribaria, and Arctia caja were shown... 

There are no drugs based on the pyrrolizidine alkaloids of the Asteraceae (e.g., Senecio and Symphytum) and Boraginaceae (Crotolaria). However, these alkaloids pose a great threat to human and animal health because of their potential for inadvertent consumption. In the case of 1,2-dehydro derivatives, such as senecio-nine, ingestion leads to non-reversible hepatotoxicity. Pyrrolizidine nucleus formation from two units of ornithine is shown (Fig. 24). 

C,gH27NO Mr 337.42, mp. 129°C, [aJo -59° (C2H5OH). P. is a pyrrolizidine alkaloid from various genera of the Asteraceae, tribe Senecioneae (Adeno-styles, Senecio, Petasites). It exists in the plants as the (V-oxide. P. does not exhibit hepatotoxicity, isrelatively non-toxic, and has atropine-like activities. It was used in the former USSR for the treatment of stomach diseases. 

CigHjjNOs, Mr 351.40, mp. 217°C (207-208°C), [alg -62.4° (CHCI3), [a]o -17.6° (CjHjOH). R. is a pyrrolizidine alkaloid from Asteraceae (Senecio, Erechtites) and some Crotalaria species (Fabaceae). It exists in the plants as the A(-oxide and is highly toxic, causing liver and kidney cancer (see pyrrolizidine alkaloids). 

Pyrrolizidine alkaloids are the leading plant toxins that have deleterious effects on the health of humans and animals. Over 360 different pyrrolizidine alkaloids are found in approximately 3% of the world s flowering plants. These noxious natural products are primarily restricted to the Boraginaceae (many genera), Asteraceae (tribes Senecionae and Eupatoriae), Fabaceae (mainly the genus Crotalaria), and... 

HSS, the first committed pathway enzyme, was localized to the root endo-dermis and cortex adjacent to the phloem in S. vernalis (Fig. 2C), which might reflect a functional accommodation for systemic transport of pyrrolizidine alkaloids to the stem (259). However, HSS was found throughout the root cortex in E. cannabinum (Fig. 2D), which is a member of the Asteraceae family along with S. vernalis (170). In contrast to the general monophyletic origin of BA biosynthesis (16),... 

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. 

Plants containing 1,2-dehydro-pyrrolizidine alkaloids may cause liver necrosis to domestic animals and humans. Therefore, care must be taken not to consume plants that are known to contain pyrrolizidine alkaloids, such as the flower stalks of Petasites japonicus (Asteraceae),comfrey Symphytum officinale (Boraginaceae), and Borago officinalis (Boraginaceae). Lycopsamine was isolated as a main alkaloid of Russian comffey (a hybrid of S. officinale and Symphytum asperum) [5]. 

Larvae of the chrysomelid beetle Oreina cacaliae produce seniciphylline A -oxide (12) as a part of their defensive secretions. This pyrrolizidine alkaloid probably is derived from the alkaloids of the host plant Adenostyles leucophylla (Asteraceae Senecioneae) (Pasteels et al., 1988). 

A variety of pyrrolizidine alkaloids and their N-oxides have antitumor activity (Wink, 1993b). Herbal material of Senecio vulgaris (Asteraceae) has been used for hundreds of years as a treatment for cancer. The active compounds have been shown to be senecionine (5) and senecionine N-oxide. Indicine N-oxide (16) from Heliotropium indicum (Boraginaceae) has pronounced antitumor activity. Mono-crotaline (8), from several Crotalaria species (Fabaceae), has similar activity (Blasko and Cordell, 1988 Suffness and Cordell, 1985). Alkylation seems to be involved in the antitumor activity. As the A -oxides cannot serve as enamines and hence cannot be directly involved in alkylation, these compounds should only be active to the extent they are converted to the free bases. At least in the case of indicine iV-oxide (16), this does not appear to be the case (Suffness and Cordell, 1985). 

The pyrrolizidine alkaloids form a toxicologically important group today they occur in some genera of the Fabaceae, Boraginaceae and Asteraceae families. TLC can also be used for identification of these substances. Some hi /-values of the alkaloids occurring most often in these plants are given in Table 76 [200]. 

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