Compositae pyrrolizidine alkaloids

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... 

Pyrrolizidine alkaloids are included in a list of alkaloids that have been isolated from the Compositae.23 All reports this year are concerned with the tribe Sene-cioneae. Definite identification of pyrrolizidine alkaloids from two new genera,... 

Pyrrolizidine alkaloids are a large family of similar chemicals found in over 6,000 different species of plants in the Leguminosae, Compositae, and Boraginacae families. For example, plants of the Senecio, Heliotropium, and Crotolaria species, many of which occur as weeds throughout the world, produce these alkaloids. About half of the pyrrolizidine alkaloids have... 

Zhao, X., Chan, M., and Ogle, C. 1989. The identification of pyrrolizidine alkaloid-containing plants—a study on 20 herbs of the Compositae family. Am. J. Chin. Med. 17, 71-78. 

Rosmarinine (54) was isolated from S. rosmarinifolius Linn (Compositae family) and upon hydrolysis afforded the necine base (-)-rosmarinecine (20) biosynthesis of 20 is well understood. The X-ray crystal structure of rosmarinine has been reported. The necine portion of 54 has been found in other pyrrolizidine alkaloids such as neorosmarinine (55), petitianine (56), angularine (58) and 12-<9-acetylrosmarinine (59)." In... 

Pyrrolizidine alkaloids from Compositae and Boraginaceae species... 

There are numerous plants containing pyrrolizidine alkaloids (PAs) and they mainly belong to the Boraginaceae, Compositae and Leguminosae families [31,47, 48],... 

Pyrrolizidine alkaloids are synthesized in plants, e.g. in Compositae, Papiliona-ceae, Boraginaceae and Leguminosae. 

As part of their extensive chemotaxonomic studies on the Compositae, Bohlmann etal (39—45) have recently discovered several new types of pyrrolizidine alkaloids with a dihydropyrrolizine nucleus in Senecio species. These are all neutral compounds. The senampelines, which occur as isomeric mixtures that have not yet been separated, contain the triol (19) of unidentified stereochemistry (Table 3T). Another series of compounds contains the related oxidised dihydropyrrolizinone (20) which occurs naturally with either 7 a or 713 stereochemistry as part of the macrocyclic diester system (Table 3U). 

In their study of neutral, terpenoid metabolites from the Compositae, Bohlmann and his co-workers have discovered a series of dihydro-pyrrolizinone derivatives in Senecio species (Table 3 U). These are all macrocyclic diesters containing 12-membered rings, although it is interesting that macrocyclic diesters with both a and p stereochemistry at C-7 of the necine have been isolated. A related series of open chain esters, the senampelines (Table 3 T), have also been discovered. This work does indicate the need to carry out careful examination of both basic and neutral fractions from plant extracts when searching for pyrrolizidine derivatives. The extent of these new derivatives should also be ascertained by reinvestigating species of other families known to contain pyrrolizidine alkaloids. 

Pyrrolizidine (1) and its derivatives have attracted the attention of chemists during the last two or three decades because this bicyclic system occurs in a number of alkaloids from various families of Compositae, Boraginaceae, Leguminosae, etc. Structural analysis of these substances, study of their reactions, and attempted syntheses have afforded considerable information concerning the chemistry of this class of compounds. Although the field has been covered by a... 

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