Biosynthetic classification

Or they may be grouped according to the genus of their plant source (morphine and codeine, Section 23-2, are examples of opium alkaloids), or by their physiological effects (antimicrobials, antibiotics, analgesics), or by similarities in the route by which they are synthesized by the organism (biosynthesis). The structural and biosynthetic classifications make the most sense to the chemist and is the organization chosen here. 

Today, despite recent developments in combinatorial and other chemosynthetic strategies, flmgi and streptomycetes remain the most prolific sources of new candidate drugs and agrochemicals. Both phyla elaborate bicyclic, tricyclic and tetracyclic fused ring polyketides, however, a preliminary survey of isotopically labelled precursor incorporation studies has revealed a consistent difference in the modes of cyclisation by which their characteristic polybenzenoid metabolites are formed. These and subsequent observations (yide infra) provide the basis for a novel biosynthetic classification of microbial fused ring polyketides. 

A GENERAL RULE FOR THE BIOSYNTHETIC CLASSIFICATION OF FUNGAL AND STREPTOMYCETE FUSED RING AROMATIC POLYKETIDES... 

Two chapters in section five describe different aspects of the biosynthesis of polyketides, which are numerically the most abimdant and structurally diverse class of natural products. The first chapter reports in vivo and in vitro studies aimed at enhancing our understanding of the basic pathways of polyketide assembly with a view to producing novel compounds. In the second chapter, a consistent difference in the modes of cyclisation of the fused ring polyketides of fungi and streptomycetes is described, which provides the basis for a new biosynthetic classification of these metabolites. 

This chapter describes typical sponge metabolites according to the biosynthetic classification, with references to their important roles in drug discovery as well as in marine ecosystems. To avoid duplication, those compounds described in Comprehensive Natural Products Chemistry are not described in detail here. We do not deal with freshwater sponges, from which only lipids and steroids were reported, except for okadaic acid from the Baikalian sponge Lubomirskia baicalensis ... 

Even though, the classification based on chemical structures is important, the biosynthetic classification seem to be more convenient. Thus, a lot of these compounds, related from a chemical point of view, in many reviews are included in the same group, though they come from very different taxonomic sources. Those products must have been originated through quite different biosynthetic routes. 

Termination step (radical), 141 Terpenoid. 202-204, 1070-1078 biosynthesis of, 1071-1078 classification of, 1071 DXP biosynthetic pathway of, 1071... 

Fig. 6 Classification of Plusiinae pheromones based on their biosynthetic pathways. Species of each group inhabiting Japanare as follows, A Trichoplusia ni [2] and Autographa gamma...

An alternative classification scheme was introduced in 2002 and this divides lantibiotics into two subgroups, class I and class II. This scheme primarily classifies lantibiotics according to their biosynthetic enzymes and sequence homology of their leader peptides. Similar to most biosynthetic pathways in bacteria, the genes for lantibiotic biosynthesis are clustered. They have been designated the generic locus symbol Ian, with a more... 

Proanthocyanidins and Procyanidins - In a classical study Bate-Smith ( ) used the patterns of distribution of the three principal classes of phenolic metabolites, which are found in the leaves of plants, as a basis for classification. The biosynthesis of these phenols - (i) proanthocyanidins (ii) glycosylated flavonols and (iii) hydroxycinnamoyl esters - is believed to be associated with the development in plants of the capacity to synthesise the structural polymer lignin by the diversion from protein synthesis of the amino-acids L-phenylalanine and L-tyro-sine. Vascular plants thus employ one or more of the p-hydroxy-cinnarayl alcohols (2,3, and 4), which are derived by enzymic reduction (NADH) of the coenzyme A esters of the corresponding hydroxycinnamic acids, as precursors to lignin. The same coenzyme A esters also form the points of biosynthetic departure for the three groups of phenolic metabolites (i, ii, iii), Figure 1. 

The C-Homoerythrina alkaloids are a relatively recently identified group, the first examples being isolated and identified from Schelhammera pedunculata F. Muell. in 1968 (81). Homoerythrina alkaloids have been isolated from all three species of Schelhammera (Liliaceae), in which they constitute a further addition to the various biosynthetically related alkaloids within the family Liliacea (82-85)-, from the leaves of species of Phelline (Ilicacea), where their presence raises some doubts about the taxonomic classification of the genus (86-88)-, and from the roots and stems of species... 

Since Hirata et al. began research into daphniphyllum alkaloids in 1966, a number of new alkaloids have been discovered. As a result, the number of known daphniphyllum alkaloids has grown markedly in recent years to a present count of 118 (compounds 1-118). These alkaloids, isolated chiefly by Yamamura and Hirata et al. are classified into six different types of backbone skeletons [1-3]. These unusual ring systems have attracted great interest as challenging targets for total synthesis or biosynthetic studies. This chapter covers the reports on daphniphyllum alkaloids that have been published between 1966 and 2006. Since the structures and stereochemistry of these alkaloids are quite complex and the representation of the structure formula has not been unified, all the natural daphniphyllum alkaloids (1-118) are listed. Classification of the alkaloids basically follows that of the previous reviews [1,2], but sections on the newly found skeletons have been added. 

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