Alkaloids, biosynthesis definition

The terpenoid indole alkaloids are a group of plant bases derived by multiple variation on the strictosidine [(79) p. 20] skeleton. Arguably the most important work in the past five years has been done on these alkaloids with enzyme preparations from plant tissue cultures, and the research is of great potential significance for other studies in alkaloid biosynthesis. The results have allowed close definition of the early stages of biosynthesis (this Report, p. 19). Use of crude enzyme preparations in this way has been extended to the study of benzylisoquinoline biosynthesis, with enzyme-catalysed formation of norlaudanosoline-1-carboxylic acid [(57) p. 16] this compound had earlier been identified as the first of the benzylisoquinolines (this Report, p. 15). It seems that amino-acids of this general formula (6) are key intermediates in the biosynthesis of all isoquinoline alkaloids. Lophocereine (7) is exceptional in that two routes (from leucine and mevalonate) may lead to it, only one of which potentially involves an acid like (6). ... 

A definite picture of the biosynthesis of norpluviine (10), the key intermediate to the pyrrolophenanthridine, and the lycorenine-type alkaloids was derived from two sets of feeding experiments. 

Securinine.—Further details of one group s study of the biosynthesis of securinine (13) have been published.21 The origins of this alkaloid are well defined,22 and information which adds to this definition is that tyrosine is incorporated without loss of tritium from the carbon atoms flanking the phenolic hydroxy-group.21... 

The biosynthesis of betalains provides a rare example of the cleavage of an aromatic ring in higher plants. The conversion of alkaloids of the type (103) into (106) provides another these results do not allow definition of the manner in which ring cleavage occurs since both intra-diol (C-15—C-16) and extra-diol (C-16—C-17) cleavage may lead to loss of C-16 and retention of tritium at C-17 as observed. 

Furoquinoline Alkaloids.—Definitive studies on the biosynthesis of furoquinoline alkaloids which had been reported in preliminary form have now appeared as... 

Interest in enzyme stereospecificity and the stereochemistry of prochiral centres, such as the methylene groups of mevalonic acid, has necessitated more precise definitions of the stereochemistry of the various molecules involved and of the enzymological consequences. The use of multiply labelled mevalonic acid in terpenoid and steroid biosynthesis has been reviewed by Hanson. The Proceedings of the 1970 Phytochemical Society symposium have been published. They include a general discussion of terpenoid pathways of biosynthesis by Clayton and specific chapters on monoterpenoids, diterpenoids, eedysones, carotenoids, isoprenoid quinones, and chromanols. Other reviews concerning biosynthesis have appeared on furanocoumarins, indole alkaloids, monoterpenoids, and diterpenoids. ... 

The present review will focus on progress made in the elucidation of the biosynthesis of tropane and related alkaloids from a more chemical perspective and will attempt to outline what in our current understanding is deficient and to identify the remaining problems. For this purpose, the discussion will be divided into two parts, dealing with the assembly of the amino acid derived C4N portion, C-l,C-5,C-6,C-7,N-8, of the five-membered ring and then with the assembly of the acetate derived C3 fragment, C-2,C-3,C-4, and the formation of the azabicy-clooctane system. A liberal definition of the term tropane wiU be used, so that the biosynthesis of cocaine and some biogenetically related pelletierine-type alkaloids may be included in the discussion. In the view of this author, results... 

Little secure information exists on the detail of biosynthesis between cadaverine and the various alkaloids although the incorporation, in appropriate fashion, of three molecules of radioactive A -piperideine 6.18) into lupanine 6.54) has been recorded label from C-6 appeared at C-2, C-15, and, by inference, C-10, whereas C-2 label appeared at C-17, C-11, and, by inference, C-6 [38]. (Much less definitive results were obtained for matrine [36].) This was taken, together with a careful consideration of the chirality at the asymmetric centres of all the quinolizidine alkaloids, as evidence for rearrangement within the A -piperideine trimer 6.59) [38], formed from 6.18), leading to the quinolizidine alkaloids [38]. 

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). 

Figure 1.18a. Proposed metabolic grid for the biosynthesis and interconversions of quinolizi-dine alkaloids and related products in Fabaceae (Papilionaceae). For definition of symbols, see Table 1.2. Construction of the metabolic grid of lupine alkaloids The data on the various conversions of the lupine alkaloids were used to construct short metabolic pathways. Data concerning the distribution of lupine alkaloids in Leguminosae were drawn from Boit (1961) Cranmer and Turner (1967) Mears and Mabry (1971) Aslanov et al. (1972) Wicky and Steinegger (1965) Faugeras and Paris (1968) Bratek and Wiewiorowski (1959) Balcar-...

At the present time about 3,000 alkaloids are known which are distributed among almost 4,000 plant species. In view of their profusion, it is not surprising that not all of the compounds that are usually considered as alkaloids meet fully the definition given above. Alkaloids are also not limited to plants a few have been demonstrated in animal organisms. Furthermore, not all compounds so classified are basic. Exceptions to this rule are, for example, nicotinic acid, colchicine and the betacyanins. Finally, the N is not always contained in a heterocycle, as can be seen from the structural formula of colchicine. However, these exceptions are usually included in the alkaloids because their biosynthesis leaves no doubt as to their close relationship to true alkaloids. 

Cocaine Biosynthesis.- The first definitive work on the biosynthesis of the tropane moiety of this alkaloid has appeared " . ... 

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