Alkaloids classification

Figure 7.1 Stemona alkaloid classification based on biosynthetic origins.

The alkaloids nomenclature has not been systematized. The commonly used systems for alkaloid classification are designed according to the plant genera or to the basis of molecular structure similarities. 

Botanical Classification of Plants Containing Tropane Alkaloids"... 

Thus, cholinergic receptor classification can be considered in terms of three stages of development. Initially, Dale [2] distinguished nicotinic and muscarinic receptor subtypes with crude alkaloids. Then, chemical synthesis and structure-activity relationships clearly revealed that nicotinic and muscarinic receptors were heterogeneous, but chemical selectivity could not come close to uncovering the true diversity of receptor subtypes. Lastly, analysis of subtypes came from molecular cloning, making possible the classification of receptors on the basis of primary structure (Fig. 11-2). 

Other reviews related to this contribution should also be mentioned, in addition to the chapters of this series, which we shall recall later. Some of these deal in general with the problem of classification of indole alkaloids and with chemo-taxonomic investigation (7-5). The chemistry of indole alkaloids is included in the Royal Society of Chemistry s Specialist Periodical Reports and has been extensively reviewed in a one-volume survey edited by J. E. Saxton (6), presenting a reasonably complete, although not exhaustive, picture of the state of the art. Other books on indole alkaloid chemistry treating this area cursorily should also be mentioned (7, 8). Recently, the genus Tabernaemontana was excellently reviewed, particularly with respect to taxonomy, phytochemistry, ethnobotany, and pharmacology (9). 

Fig. 1. Classification of indole alkaloids isolated from Tabernaemontana plants.

In addition to monomeric compounds, Tabemaemontana plants contain many bisindole alkaloids that are classified on the basis of constituent monomeric units, as in the extensive review by Cordell and Saxton in Volume XX of this series (14). This classification is more rational and comprehensive than others (I, 13, 15) and will be used as a guide for the representation of structural formulas and for the discussion of the chemistry of single alkaloids. 

Some alkaloids do not fall into the simple classification that we have used, nor do they fall into the categories that we have decided to exclude. In this chapter,... 

Enzymes involved in alkaloid transformations have been arbitrarily divided into two major classes or types of biotransformations. The classification used here is that which has evolved from early descriptions of mammalian detoxica-... 

Occurrence, Classification, and Biological Activity of Carbazole Alkaloids. 116... 

Classification based on physiological activity The interest in natural products is frequently initiated by attempts to isolate and clarify a physiologically active principle of plant or animal origin. Actually, many medicines currently in use are natural products, e.g. alkaloids, such as morphine and penicillin G. 

Muscarine is a natural alkaloid that is found in a number of wild mushrooms. Despite the fact that muscarine does not have any therapeutic value, it is of interest because of its expressed toxic properties, which made it one of the first systematically studied cholinomimetic substances. This compound was an underlying classification of cholinergic muscarinic receptors. The action of muscarine is similar to that of acetylcholine on peripheral autonomic effector organs, and atropine is an antagonist to it. Unlike acetylcholine, muscarine does not act on nicotinic receptors. 

In this series, three earlier reviews on carbazole alkaloids were published by Kapil (1), Husson (2), and Chakraborty (3) in the Volumes 13,26, and 44, respectively. The present chapter introduces a new classification of carbazole alkaloids and summarizes the recent synthetic efforts. The nomenclature of carbazole alkaloids used in this review is that of Chemical Abstracts. As shown in Scheme 1.1, the conventional tricyclic ring system of carbazole 1 is denoted by A, B, and C, and the numbering starts from ring A. The term carbazole generally refers to a 9H-carbazole. 

The presence of pavines and isopavines has been used to provide assistance for taxonomic classifications, and to determine intergeneric and phylogenic relationships in the genera Papaver and Argemone. The results of extensive chemical research on Papaver species demonstrated that morphologically distinct sections are also chemically distinguishable by virtue of their alkaloidal profile (170). Out of nine well-defined sections of Papaver, the Section Scapiflora, which displays... 

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