Of sesquiterpene alkaloids

Several classes of sesquiterpene alkaloids have been reported these do not appear to be closely related biosyntheti-cally. Important among these alkaloids are those of Nuphar and Dendrobium (Orchidaceae), and the Celastraceae and Hippocrateaceae. About 130 sesquiterpene alkaloids are known (Verpoorte et al., 1991). 

Fig. 36.6. Some miscellaneous types of sesquiterpene alkaloids and pulchellin.

The dopaminergic potential of the Dendrobium species is, to date, open for exploration. An interesting feature of the Dendrobium species is their ability to elaborate sesquiterpene alkaloids, the chemical structure of which resembles the one of strychnine. One such alkaloid is dendrobine, which is widespread in the genus. Kudo et al. noted that dendrobine, isolated from Dendrobium nobile, exhibits a strychnine-like presynaptic inhibition in frog spinal cord (64). 

Farnesylamine (123) (Fig. 20), a sesquiterpene alkaloid, was recently detected in whole extracts of Monomorium fieldi [129]. This compound had already be prepared by synthesis and found to display a whole range of biological activities. Among others, it inhibits arthropod molting, squalene synthesis, and the growth of malignant tumor cells, modulates human T cells and has anti-osteo-porosis activity [129]. 

Figure 62. Structural development of sesquiterpene pyridine alkaloids.

Sesquiterpene lac.lones are also found throughout the family and some of these may be responsible for reports of positive alkaloid tests, inasmuch as their structural features can give positive reactions with the DragendorIT reagent. 

The first Mexican substance searched for, found, and isolated based on old traditions, was the sesquiterpene hemandulcin from Lippia dulcis Trev. It was determined by a human taste panel to be more than 1000 times sweeter than sucrose. The structure of this sesquiterpene was determined and confirmed by chemical synthesis. It was nontoxic when administered orally to mice, and did not induce bacterial mutation.5 Further work has been carried out with some of the plants more frequently used (Table 12.3). The sesquiterpene alkaloids hippocrateine I, hippocrateine II, and emarginatine were identified in Hippocratea excelsa used in Mexican traditional medicine, and antimicrobial abietane type diterpenes were isolated from Salvia albocaerulea.6 7... 

Due to their more simple structures, the syntheses of the sesquiterpene alkaloids, the dendrobines, were mastered first. 

Scheme 5. Esterifying acids of the sesquiterpene cores of khat alkaloids. (The numbering indicated is as transferred from the intact alkaloids).

Although a variety of monoterpene alkaloids and some sesquiterpene alkaloids are known, they are of little... 

The root extracts of Maytenus senegalensis have been shown to inhibit protein kinase C, as well as having lethality against brine shrimp. The dihydroagarofuran sesquiterpene alkaloids mayteine, putterine A and putterine B have been isolated from the root extracts. Quinonemethide triterpenoids, which have revealed potential anti-tumour and antimicrobial activities, are another diverse group of secondary metabolites from the related species Maytenus ilicifolia. ... 

Nupharolidine (25), a new sesquiterpene alkaloid, has been isolated from Nuphar luteum and characterised mainly by spectral means. The Dendrobium species (Orchidaceae) is known to be rich in sesquiterpene alkaloids. A taxonomic survey of Australian Orchidaceae which includes a discussion of Dendrobium has appeared. ... 

In the course of these research programmes, cytotoxic quinones, polyester sesquiterpenes and pyridine-sesquiterpene alkaloids with antifeedant and/or insecticidal properties have been isolated from Latin American species, in particular those of the Maytenus genus which is extensively used by rural communities and tribes in the Andes and the Amazon basin. Recently some sesquiterpene alkaloids with immunosuppressive activity and sesquiterpenes with antitumoral activity have also been described [3]. 

Sesquiterpene alkaloids have similar structures to polyester sesquiterpenes except that the hydroxy groups of the eudesmane basic skeleton are esterified by nicotinic acid and/or its derivatives. Little has been published about sesquiterpene alkaloids from American species which tend to be found in the roots of the plants (Table II). 

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