Ergot alkaloids classification

A. Classification and Prototypes Ketanserin is a S-HT and alpha-adrenoceptor blocker. Phe-noxybenzamine (an alpha-adrenoceptor blocker) and cyproheptadine (an Hj blocker) are also good 5-HTj blockers. Ondansetron, granisetron, dolasetron, and alosetron are 5-HTj blockers. The ergot alkaloids are partial agonists at 5-HT and other receptors (see below). 

A. Classification and Prototypes The ergot alkaloids may be divided into three major subgroups on the basis of the organ or tissue in which they have their primary effects (Figure 16-3). This division is not absolute, since most of the alkaloids have some effects on several tissues. 

The classification of the ergot alkaloids are based on the type of substituent at C-8 and are divided into four groups ... 

Classification based on botanical origin of the alkaloids are also used, e.g., Papaver (opium) alkaloids. Cinchona alkaloids, Rauvolfia alkaloids, Catharan-thus alkaloids, Strychnos alkaloids. Ergot alkaloids, cactus alkaloids, and Solanum alkaloids. The structures of some alkaloids are shown in Figure 1. 

From a historical point of view ergot alkaloids are closely linked to the classification of adrenoceptors into two major subtypes (a and / ). The discrimination between a- and -adrenoceptors was based on the insensitivity of the latter to ergot alkaloids or -haloalkylamines (Nickerson, 1949). On the basis of structural, transductional, and operational criteria it became apparent that the existence of two subtypes of a-adrenoceptors, the ai-adrenoceptor, sensitive to blockade by prazosin, and the a2-adrenoceptor, sensitive to blockade by yohimbine or rauwolscine, makes it more appropriate to classify adrenoceptors into three major subtypes the aj-adrenoceptors, az-adrenoceptors, and -adrenoceptors (Bylund, 1988). 

Komarova, E.L. and Tolkachev, O.N., The chemistry of peptide ergot alkaloids. Part I. Classification and chemistry of ergot peptides, Pharm. Chem. J., 35, 504, 2001. 

There is no uniform classification for the A. In the literature divisions according to origin (examples Aconitum, Amaryllidaceae, Aspidosperma, cactus, Catharanthus, Cephalotaxus, Cinchona, coca, Corydalis, curare, Dendrobates, ergot, Erythrina, Iboga, Lycopodium, Maytenus, opium, Rauvol-fia, Senecio, Strychnos, tobacco, Vinca alkaloids, salamander, Solanum, Veratrum steroid alkaloids) in addition to divisions according to chemical structure (examples aporphine, benzylisoquinoline, bis-benzylisoquinoline, berberine, carboline, diterpene, inudazole, indole, indolizidine, isoquinoline, lupinane, macrocyclic, morphine, peptide, / -phenyl-ethylamine, piperidine, purine, pyridine, pyrrolidine, pyrrolizidine, quinoline, quinolizidine, quinucli-dine, spermine, spermidine, steroid, terpene, tro-pane, tropolone alkaloids) are used. 

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