Alkaloids biogenetic classification

Table 7.1 Biogenetic classification and principal centres of production of major alkaloid groups...

Plants within the Euphorbiaceae family elaborate a diverse number of alkaloids most of which defy distinct biogenetic classification (1, 2). Two groups which can he distinguished are the benzylisoquinoline... 

Table I is a compilation of plant species which contain the simple indole alkaloid types of Fig. 1. As mentioned earlier, the main requirement for the inclusion of a certain simple indole alkaloid into Table I is that it contain a tryptamine unit as a readily distinguishable feature in its structure. That tryptamine is a precursor in the biosynthesis of many of the b, c, d, and e type simple indole bases is yet to be shown although it is felt that future work will prove the correctness of such a view. Gramine, the simplest indole alkaloid, has been included in the tryptamine classification a because it is biosynthetically related to tryptophan cryptole-pine has been likewise included therein although its structural relationship to tryptophan appears more obscure (Volume VIII, Chapter 1, pp. 4, 19). The calycanthine type does not possess a tryptamine structure but it is included in the simple indole alkaloid b classification since most of its congeners are tryptamine derivatives and since it exhibits a close biogenetic relationship to this latter (chimonanthine) type (Volume VIII, Chapter 16). Type d is represented by the small number of the so-called canthin-6-one alkaloids (Volume VIII, pp. 260-252, 497-498). The most recent variation of the simple indole alkaloids is found in the Anacardiaceae family. Its indoloquinolizidine nucleus suggests inclusion with type d on the basis of structural and biogenetic similarity. Finally, simple indole alkaloid type e is composed of the well-defined evodiamine (rutaecarpine) structural form (Volume VIII, Chapter 4).

Fig. 34.3. Biogenetic classification of indole alkaloids (Cordell, 1981 used with permission of the author Kompis et al., 1971).

Anthranilic acid may also be produced by metabolism of tryptophan Figure 1 Biogenetic classification of the quinolin/one alkaloids. 

Following the biogenetic classification, we first address macrolactones, divided into the main family groups that have received synthetic attention via RCM (re-sorcinylic, salycilates, other antibiotic macrolides, macrocyclic musks, epothilones, amphidinolides, other polyketides, and natural cyclophanes), then the terpenoids, followed by the macrocycles obtained from the amino acid metabolism (lactams, depsipeptides, alkaloids), and finally the glycolipids. 

It is usual to classify alkaloids (basic nitrogenous metabolites) according to the amino acids (or their derivatives) from which they arise. Thus, the most important classes are derived from the amino acids ornithine, lysine, phenylalanine, tyrosine and tryptophan, and the skeletons of these amino acids are retained largely intact in the alkaloids derived from them. However, this type of classification is often criticized because it fails to include those alkaloids that are derived from a mixed biogenetic pathway (e.g. polyketide or terpenoid) with incorporation of a nitrogen atom, ultimately from ammonia. The alkaloids that are the subject of this review are excellent examples of such compounds and they are often known as pseudoalkaloids. 

The first chapter, by Kobayashi and Morita, is a superb extension of the chapter that was published in Volume 45 of the series. It is a comprehensive review of the Lycopodium alkaloids in terms of their structural classification, distribution, and occurrence, followed by detailed discussions of their spectroscopic aspects, the determination of stereochemistry, and their biological activities. The substantial efforts made in the past few years to effect the synthesis of the diverse skeleta of this group of alkaloids from the club mosses are also presented, together with a detailed overview of their complex biogenetic interrelationships. 

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