Ricinus alkaloids

These alkaloids include the substituted pyridone ricinine [524-40-3] (53), CgHgN202, which is easily isolated in high yield as the only alkaloid from the castor bean (Ricinus communis L.). The castor bean is also the source of castor oil (qv), which is obtained by pressing the castor bean and, rich in fatty acids, has served as a gentie cathartic. 

Pyridine Group. Piperine, Piperovatine, Leucenol, Mimosine, Alkaloids of Ricinus communis, Foenugrec, vy eca Nut, Hemlock, Lobelia, Tobacco (Nicotiana spp.). Anabasis aphylla, Pomegranate Root Bark. ... 

Two pyridone alkaloids ricinine (238) and nudiflorine (239) have been isolated from Ricinus and TYewia (Euphorbiaceae), respectively (61JBC1186 64CI(L)1524). It has been shown that at least seven species in this family contain enzyme systems that can oxidize 3-cyano-l-methylpyridinium salts in... 

Nicotinic acid undoubtedly provides the basic skeleton for some other alkaloids. Ricinine (Figure 6.35) is a 2-pyridone structure and contains a nitrile grouping, probably formed by dehydration of a nicotinamide derivative. This alkaloid is a toxic constituent of castor oil seeds (Ricinus communis Euphorbiaceae), though the toxicity of the seeds results mainly from the polypeptide ricin (see page 434). Arecoline (Figure 6.36) is found in Betel nuts (Areca catechu Palmae/Arecaceae) and is a tetrahydronicotinic acid derivative. Betel nuts are chewed in India and Asia for the stimulant effect of arecoline. 

The most toxic plant product, ricin, is also the most toxic chemical known to man. Unlike the pyrrolizidine alkaloids, ricin is a protein which most cleverly targets the interior workings of cells. The way in which this most potent poison works is quite elegant (see box, p. 151). It is made and found in the seeds of the castor bean (Ricinus communis). 

Castor oH (ricinus oil). The oil obtained from seeds of the castor-oil plant or castor beans (Ricinus communis, Euphorbiaceae), mp. -10 C. It contains about 80-85% ricinoleic acid as glycerol ester together with oleic (7%), linolic (3%), palmitic (2%), and stearic (1%) acids. The Ricinus seeds contain the highly poisonous constituents ricin, a mixture of proteins, and ricinine, a pyridone alkaloid. The presence of these substances leaves the oilcake remaining after pressing of C. unsuitable for use as animal fodder. 

CgH8N202, Mr 164.16, mp. 201 °C. A pyridine alkaloid from Ricinus communis (Euphorbiaceae). Its content in this plant is 1 % and together with the extremely toxic protein ricin R. is responsible for the toxicity of Ricinus seeds. The biosynthesis of R. proceeds through nicotinamide as an intermediate. 

Plants produce various pyridine alkaloids derived from nicotinic acid. Trigonelline, the major component in coffee seeds, and ricinine, the toxic alkaloid produced by Ricinus communis, are formed from nicotinic acid originating from the NAD catabolism [20, 25, 26], Quinolinic acid was found to be an efficient precursor in the biosynthesis of nicotine [27]. 

A series of compounds that appear to be derived from nicotinic acid is found in a number of euphorbiaceous plants. Ricinine (49), an alkaloid from Ricinus communis, is derived from nicotinic acid via nicotinamide (50). This alkaloid may occur in quantities as great as 1% of the plant dry weight. A crude enzyme preparation has been isolated that will convert a series of pyridinium salts into ricinine and related compounds (Fig. 28.20) (Fodor and Colasanti, 1985). This alkaloid disappears completely from senescent leaves. Ricinine (49) has an LD50 p.o. of 42 mg/kg in Agelaius (Wink, 1993). 

Ricinin a poisonous pyridine alkaloid from seeds of Ricinus communis. M, 164.17, m.p. 201 °C, b.p.20 170-180°C.R. is an exceptional alkaloid, in that it occurs in only one type of plant and is not accompanied by other alkaloids. It is biosynthesized from nicotinic add biosynthetic precursors of nicotinic acid are as-... 

There is another application of chemotaxonomy, actually chemotaxon-omy a rebours (in reverse). A chemist, pharmacologist, or biochemist can be guided by the botanist in searching for plants which produce compounds of special interest. The castor bean plant, Ricinus communis, produces a peculiar alkaloid, ricinine. Studies by Waller et al. (1966), Essery et al. (1962), and Jackanicz and Byerrum (1966), showed some of the pathway of its biosynthesis. The genus Ricinus is monotypic, represented by the single species R. communis. No other plant among the Euphorbiaceae is known to accumulate ricinine. In 1964, a new alkaloid, nudiflorine, was isolated by... 

Plant cells are less specialized than animal cells in their metabolic abilities. An animal cell can develop or lose some metabolic properties depending on the tissue however, this process is mostly irreversible, e.g., there is no way known at present to reverse the development of a nerve cell or a liver cell into an embryonic one. This is true to some extent for plant cells also usually a leaf cell performs leaf metabolism, while a root cell performs only root metabolism. Under certain conditions, it is possible to change the metabolic properties. It was shown by Steward (1964) that carrot root cells, when released from the limitations of their normal tissue environment, can undergo differentiation to form all possible types of cells, leading ultimately to an entire plantlet. Some leaves or pieces of stem can readily form roots. Therefore, owing to this metabolic versatility, one might expect that alkaloids can be formed in all cells of a plant. This may be the case in some plants, such as Ricinus communis (castor bean), but it is not universal. 

Figure 4.6. Ricinus communis (castor bean) leaf fed a foreign alkaloid (sparteine). Alkaloid accumulated in intercostal field and close to the edges of the leaf will not be transported away from the leaf. Some of the poorer precursors, such as nicotinonitrile, behave similarly. Shown is a drawing for original see Nowacki and Waller (1972).

Floss et al. (1974) have recently published a review entitled Regulatory Control Mechanisms in Alkaloid Biosynthesis. While the article is not all-inclusive on the subject of alkaloid biology and metabolism, we will use some of its arguments and examples, since it represents the first extensive treatment of the subject of regulation. The pyridine alkaloids, e.g., nicotine, anabasine, and ricinine, have a special relationship to primary metabolic reactions that occur in Nicotiana spp. and Ricinus communis, The control mechanism appears to involve the regulation of the pyri-... 

Ricinine in Ricinus communis and Quinolizidtne Alkaloids in Leguminosae... 

Biotransfonnations of Alkaloids.—For a long time it was considered that alkaloids were end-products of metabolism. However, it is now being realized that many of them are rapidly metabolized, either to other alkaloids, or to non-alkaloidal compounds. Waller and co-workers have carried out extensive work in the past few years on ricinine metabolism. In senescent leaves of Ricinus communis, ricinine (18) is demethylated to N-demethylricinine (19). In... 

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