Alkaloids from Lower Plants

Eight alkaloids of the carbazomycin group have been reported. The structures of these alkaloids were deduced on the basis of the detailed structural studies of carbazomycin B discussed previously 11). 

NMR spectrum was similar to that of carbazomycin C except for the presence of additional methoxy signal which replaced the signal of the hydroxyl group in carbazomycin C. Carbazomycin C on methylation with dimethyl sulphate and alkali gave carbazomycin D. Evidently, carbazomycin D is 1 2-dimethyl-3-4,6-trimethoxycarbazole which is also supported by the C-NMR spectrum 86). 

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The Chelsea group also examined the distribution of alkaloids in young plants of M. parvifolia grown from seeds obtained from Sri Lanka (97). During this study these authors were able to resolve one of the major problems, namely, the role of mitraphylline (149) in the biosynthesis of Mitragyna alkaloids. Mitraphylline was found only in the lower part of the... 

Subsequent attempts to repeat the isolation of these alkaloids from plants collected from the same area in Queensland have so far met with failure markedly lower yields of alkaloids were obtained, and these appear not to be tropane alkaloids. Since the leaves originally shown to contain the three tropane alkaloids were carefully identified it appears that P. mearsii must be very variable in alkaloid content, or possibly that the tropane alkaloids, if present, are normally lost during the drying of the leaves. 

In a previous paper [1], we reviewed the isolation of quassinoids, alkaloids, and fatty acids from Simaroubaceous plants during the period 1972-1988 and discussed their biological activities, such as antitumor, antimalarial, and anti-inflammatory agents as well as insect antifeedants, amoebicides, and herbicides. This review will add new quassinoids isolated from Simaroubaceous plants from 1988 onwards and their biological activities, for example, antitumor, anti-tumor-promotor (= inhibitor against TPA-induced EBV-EA activation), anti-HIV, anti-tuberculosis, and insect antifeedant activities. Furthermore, the stability of quassinoids, lower activities of degradation products, and the synthesis of fluorinated quassinoids are also described. 

The molecular skeleton of infractopicrin resembles that of vincamine, a representative alkaloid which lowers blood pressure, isolated from plants of the genus Catharanthus (Vinca). There is, however, no evidence of a biogenetic relationship of these alkaloids, and the absence of an angular ethyl group in infractopicrin and in the accompanying metabolites suggests rather different biosynthetic pathways in both cases (177). Studies on the canthin-6-one alkaloids of various natural origins were recently reviewed by Ohmoto and Koike in Volume 36 of this treatise (179). 

Alkaloids are found most commonly in dicotyledonous angiosperms and are uncommon in algae, bryophytes, ferns, and monocotyledonous angiosperms. However, alkaloids are known from the lower plant Lycopodium, and from the monocotyledonous families Amaryllidaceae, Dioscoreaceae, Liliaceae, Orchidaceae, and Poaceae. Alkaloids are not common in gymnosperms, although they are encountered in several conifers and occasionally in other gymnospermous groups. 

While the higher plants are the major sonrce of alkaloids, they are also known to occnr in lower plants snch as horsetails, in algae, fnngi, microorganisms, insects and even the organs of mammals (Kapoor 1995). Over 10 000 different alkaloids have been isolated from over 300 plant families (Raffanf 1996). They may be fonnd in roots, rhizomes, leaves, bark, frnit or seeds. Over 40 alkaloids may occnr in a single plant, for example Vinca major. 

Antihypertensive agents, substances that lower high blood pressure, are an important subclass of cardiovascular agents. Reserpine, an indole alkaloid obtained from the Rauwolfia plant, was the first successful drug to... 

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