Cinchonine, biosynthesis

Protein biosynthesis is essential for all cells and thus provides another important target. Indeed, a number of alkaloids have been detected (although not too many have been studied in this context) which inhibit protein biosynthesis in vitro. Emetine from Cephaelis ipecacuanha (Rubiaceae) is the most potent plant constituent other alkaloids with the same ability include harringtonine, homoharringtonine, cryptopleurine, tubulosine, hemanthamine, lycorine, narciclasine, pretazettine, pseudolycorine, tylocrepine, and tylopherine [5] and furthermore, ajmaline, berberine, boldine, cinchonine, cinchonidine, harmalin, harmin, lobeline, norharman, papaverine, quinidine, quinine, salsoline, sanguinarine,... 

Biosynthesis In vivo experiments with the labeled ketone of C. (=cinchonidinone) revealed its incorporation into the Cinchona alkaloids, especially in non-methoxylated members such as C. and cinchonine. For enzymatic studies, see. Lit., for synthetic investigations, see Lit.. The uses of C. are similar to those of quinine. 

Despite the fact that quinine (66) and related alkaloids have quinoline skeleta biogenetically, they are indole alkaloids. Radioactivity from labeled loganin (11) and strictosid-ine (3) is incorporated into quinine. The indole nitrogen becomes the quinoline nitrogen (Fig. 34.19). Loganin (11), corynantheal (69), and probably cinchonamine (70) have been shown to be key intermediates in the biosynthesis of quinine (66), cinchonine (67), and cinchonidine (68) (Kapil and Brown, 1979). 

Actually there are no good definitions of alkaloids (Bate-Smith and Swain, 1966) since each one is either too narrow or too broad. Even in the restricted Winterstein and Trier definition, at least five alkaloid families exist that can be derived from different amino acids consequently, there is a need to establish the proper biosynthetic pathways to permit the application of the alkaloid character to chemotaxonomy, It has been mentioned above that canadine (berberidine) may be found in plants of six partially unrelated botanical families. This fact is not surprising when considered in relation to the biochemical investigations of canadine biosynthesis. Many reactions are necessary to convert tyrosine into canadine consequently, one might even wonder why the distribution of this alkaloid is so limited. In contrast, other plants (and even some that produce canadine) can produce many alkaloids that are derived from tyrosine but have a marked difference in structure. Tyrosine serves as the key precursor of alkaloids of the isoquinoline type, but other types of alkaloids, such as colchicine and the Amaryllidaceae and the Erythrina alkaloids, may be synthesized from this amino acid. The nucleus of an alkaloid molecule can arise from different precursors thus the indole nucleus in Erythrina alkaloids arises from tyrosine, while in brucine it comes from tryptophan (Figure 1.5). The alkaloids cinchonamine and cinchonine differ in that cinchonamine has an indole nucleus, while cinchonine (like quinine) has a quinoline nucleus however, they exist in a precursor-product relationship (that is, the quinoline type is derived from the indole type in a one-step reaction). 

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