Structure of Halogenated Alkaloids

Modem Alkaloids Structure, Isolation, Synthesis and Biology. Edited by E. Fattorusso and O. Taglialatela-Scafati Copyright 2008 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31521-5 

The marine bryozoan Plustrafoliacea is a prolific source ofbrominated indoles [18], including several prenylated examples, such as 12 [19], 13 [20,21], 14 [21], and hexahydropyrrolo[2,3-b]indol-7-ol (15) [21]. An excellent review of marine alkaloids including those from bryozoa is available [18]. 

Another large group of brominated tryptophan-derived marine alkaloids are the aplysinopsins and several new examples have been reported. The sponge Hyrtios erecta has furnished 20 and 21[26], while a New Zealand asddian is the source of kottamides A-E, for example A (22) [27] and E (23) [28], The stony coral Tubastraea sp. contains the structurally complex and unprecedented bisindole tubastrindole A (24) [29]. 

The Philippine ascidian Perophora namei has yielded the polycydic alkaloid perophoramidine (30), which is the first reported metabolite from the genus Perophora [35]. A Far Eastern Eudistoma ascidian was found to contain two bromi-nated ergoline alkaloids pibocins A (31) [36] and B (32) [37]. 

Unlike carbazoles, haiogenated (3-carbolines are abundant in nature [1[. For example, the simple eudistomin O (7-bromo-(3-carboline) (40) is a ubiquitous marine ascidian metabolite [44[. Indeed, the tunicate genus Eudistoma has furnished most of the extant haiogenated (3-carbolines, some of which have significant antiviral (polio, herpes) and microbial activity. The Caribbean Eudistoma olivaceum produces at least 15 brominated carbolines [1[. A study of Eudistoma gilboverde uncovered the new eudistomins 41-43[45[, and the Australian ascidian Pseudodistoma aureum has 

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Figure 31. Selected Structures of halogenated indole alkaloids alkaloids isolated from Laurencia species.

Of the more than 4500 known naturally occurring organohalogen compounds, a large fraction are alkaloids [1,3]. Most of these halogenated pyrroles, indoles, carbazoles, carbolines, tyrosines, and others have a marine origin. The present chapter surveys the occurrence, structure, and biosynthesis of these fascinating natural products. However, given their sheer number, this review focuses mainly on recent examples. 

The most important group of structural isomerides of the cinchona alkaloids are the quinicines or quinatoxines (formula F, CH3. CHOH. —>CHa CH. ) of which only one, quinicine (p. 425) occurs naturally. Other transformation products have been obtained mainly by three methods (a) heating the alkaloids with 50 to 70 per cent, sulphuric acid, (b) heating them under pressure with hydrochloric acid (sp. gr, 1-125), or (c) the action of water, alkalis or silver nitrate on the halogen acid addition products (D) of the four cinchona alkaloids containing a vinyl side-chain. The nature of the products of these reactions was first worked out for cinchonine mainly by Skraup and his collaborators and by Jungfleish and L ger. ... 

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