Indoles halogenated alkaloids

This section and the section on alkaloids in the first survey (7) are artificially small since many halogenated alkaloids are presented in the sections on pyrroles, indoles, carbolines, tyrosines, and other nitrogen heterocycles. It might be noted that the very large number of brominated alkaloids that are obviously tyrosine-derived are now included in Sect. 3.22.3 (Tyrosines). 

Rahbaek L, Anthoni U, Christophersen C, Nielsen PH, Petersen BO (1996) Marine Alkaloids. 18. Securamines and Securines, Halogenated Indole-Imidazole Alkaloids from the Marine Bryozoan Securiflustra securifrons. J Org Chem 61 887... 

Perophoramidine (15), halogenated alkaloid, was isolated from the Philippine ascidian Perophora namei Hartmeyer and Michaelson (Perophoridae) [36a]. This compound contains fused hexahydropyrrolopyridine, indole and dUiydroquinoline rings. Amidine parts exist at the fusing part of the indole and quinoline rings. The stereochemistry was determined by... 

Anthoni U, Bock K, Chevolot L, Larsen C, Nielsen PH, Christophersen C (1987) Marine alkaloids. 13. Chartellamide A and B, halogenated [l-lactam indole-imidazole alkaloids from the marine Bryozoan Securiflustra securifrons. J Org Chem 52 5638-5639... 

The bryozoan Securiflustra securifrons (Flustridae) produces the halogenated indole-imidazole alkaloids... 

In thematic volumes of The Alkaloids seminal developments in areas of exceptional interest are summarized and highlighted. The previous thematic volume of this series. Volume 71, focused on halogenated alkaloids. In Volume 76, aU four chapters are devoted to indole alkaloids, one of the supreme fields in alkaloid chemistry. 

Anthoni, U., Block, K., Chevolot, L., Larsen, C., Nielsen, P. H., Christophersen, C. Chartellamide A and B, halogenated y0-lactam indole-imidazole alkaloids from the marine bryozoan Chartella papyracea. J. Org. Chem. 1987, 52, 5638-5639. 

A new halogen-containing member of the penitrem family of indole-diterpe-noids, which have insecticidal activity (1397), is thomitrem A (1466) from Penicil-lium crustosum (1398). The novel dichlorinated calmodulin inhibitor, malbrancheamide (1467), was characterized from the fungus Malbranchea auran-tiaca (1399). The microbe Streptomyces rugosporus produces pyrroindomycin B (1468), which is active against both methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci (1400). The Chinese shrub Acacia confusa has yielded the unusual chlorotryptamine alkaloid 1469, which does not appear to be an artifactual dichloromethane adduct (1401). 

Another interesting application of microwave irradiation is found in the selective dehalogenation of the iodinated indole alkaloid Plakohypaphorine F, described by E. Fattorusso et al. [117,118] (Scheme 32). The bis-halogenated compound was treated with potassium formate and palladium acetate under controlled microwave irradiation, resulting in selective deiodination. The choice of the solvent, in this case DMSO, was found to be crucial. 

As the azocinoindole 40 constitutes the tricyclic substructure of the indole alkaloid apparicine , we attempted to improve the cyclization yield. Satisfactorily, the regioselectivity was completely switched to the 8-endo mode when the alkene acceptor was substituted at the internal position by a bromine atom. Thus, cyclization of selenoester 43 led to the desired target 40 as the only reaction product in 75% yield. Clearly, the bromine atom not only sterically prevented the competitive 1-exo attack, but also benefited the cyclization by activation of the double bond. It should be noted that similar halogen-controlled 8-endo cyclizations are known in the literature, but involving amidyl-type radicals <06OL2647>. 

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. 

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