Biogenesis of alkaloids

The key step of the synthesis, which involved a classical Mannich condensation in the synthesis by Evans and Scott (as well as in the biogenesis of alkaloids in general [10]), is substituted by a 1,3-dipolar cycloaddition of a nitrone to a carbon-carbon double bond [11] which provides an alternative route for the formation of a new C(l)-C(2) bond with the concomitant creation of a 1,3-consonant relationship between an oxygen atom and a dialkylamino group. In order to arrive at a typical Mannich base two more steps are, however, necessary. The similarity between the two processes is shown is Scheme 13.2.7 ... 

Biogenetic pathways leading to naturally occurring pyrrolizidine bases were proposed by Robinson, Schopf, and Lukefi (see, e.g., refs. 119-121) in their publications concerned with the biogenesis of alkaloids. The most probable precursors of the pyrrolizidine system are commonly accepted to be ornithine (176), hydroxyomithine (177), and their biogenetic equivalents. It is noteworthy that ( + )- -hydroxy-jV-methylnorvaline (178) (structurally related to ornithine) was isolated... 

The biogenesis of alkaloids has been studied from the beginning of the past century, first to determine their structures and subsequently to study their biosynthesis in plants (Mothes et al, 1985). Detailed h)q)otheses of alkaloid... 

There is evidence that both these routes can occur. The enzymes converting tryptophan to indoleacetic acid can be obtained in maize embryo juice the tryptophan is thought to arise from the endosperm (964). Indolepyruvic acid is also present in maize endosperm (837, 838), suggesting it to be an intermediate. On the other hand, tryptamine is converted to indoleacetic acid in plants (304, 815) and the amine oxidase responsible has been studied by Kenten and Mann (464). Consideration of the biogenesis of alkaloids, discussed later, suggests that both tryptamine and indoleacetaldehyde are likely to occur in plants. 

This applies especially to substances such as the essential oils or lignin. The comparatively small amount of tvork so far done on the biogenesis of alkaloids from isotopically labeled amino acids suggests that theories of biogenesis of alkaloids from amino acids are probably justified. 

The biogenesis of alkaloids from the aromatic amino acids forms an enormously rich field for work with modern isotopic and chromatographic techniques, which as yet has hardly been touched. 

A possible mode of biogenesis of alkaloids of the cularine type has been simulated by the oxidation of l-(4-hydroxy-3-methoxybenzyl)-8-hydroxy-6,7-dimethoxy-2-methyltetrahydroisoquinoline to the dienone (164), and rearrangement of this... 

The Total Synthesis of Talatisamine.—The atisine-type intermediate (62) has been used in the synthesis of talatisamine (63).A key step in this synthetic route is the rearrangement of an atisine skeleton (structure B) to a lycoctonine skeleton (structure A). This type of rearrangement has been proposed in the biogenesis of alkaloids possessing the lycoctonine skeleton. Johnson and Overton S and Ayer and Deshpande have previously reported studies of this process. 

The parent compound of the secoiridoids is secologa-nin (see secoiridoids), the most important intermediate in the biogenesis of alkaloids that are not derived from an amino acid. This includes most indole alkaloids, the ipecac, the Cinchona, and the pyrroloquinoline alkaloids as well as simple monoterpene alkaloids The best known biological property of the I. is their bitter taste. However, bitter principles are mostly not used as pure substances, instead alcoholic extracts are preferred to stimulate appetite (increased secretion of gastric juice). Furthermore, bitter substances are used to modify the taste of pharmaceutical products. Some I. exert various effects on the central nervous system as a consequence of their volatility and lipophilicity, e.g., nepetalactone, iridodial, teucrium lactones, and valepotriates. 

Mothes, K., Biogenesis of alkaloids and the problem of chemotax-onomy, Lloydia, 29, 156-171 (1966b). 

The experimental testing of the earlier suggestions that iV-norlaud-anosoline (CXXXVIII R = H) and laudanosoline (CXXXVIII R = CH3) were possible precursors in the biogenesis of alkaloids in plants has provided a stimulus for their further study. 

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