Other Bromopyrrole Alkaloids

The first examples of tetrameric pyrrole imidazole alkaloids, stylissadine A (100) and B, were isolated from the Caribbean sponge Stylissa carihica in 2006 [128]. They possess a symmetric dimeric stmcture derived from condensation of two massadine units, and differ in the configuration at the center C-2. Stylissadines represent the largest pyrrole-imidazole alkaloids isolated so far, and, with their 16 stereogenic centers, they are the most complex stmctures known within the oroidin alkaloid family. 

Several simple bromopyrroles (101-109) have been isolated from Agelas oroides (101, lOS) [129,1], Agelas flahelliformis (101, 102) [130], AoantheUa carteri (103, 104) [131], Agelas nakamurai (106, 107) [132], Homoaxinella sp. (108) [133], and AxineUa 

A spermidine derivative with two 4,5-dibromopyrrole-2-carbamyl units, pseudo-ceratidine (120), has been isolated from the sponge Pseudoceratina purpurea as an antifouling compound [145]. 

Two syntheses of pseudoceratidine (120), which was reported to inhibit metamorphosis of the barnacle Balanus amphitrite, have been described [146,147]. To delineate the structural requirements for this bioactivity, the corresponding N-1 and N-8 mono-(4,5-dibromo-2-pyrrolyl) amides of spermidine were also synthesized, as well as the closely related mono- and bis-(4,5-dibromo-2-pyrrolecarboxamido) residues to test the importance of the pyrrole substituents and the positively charged secondary amine group in 120 [148]. 

Clathramides A-D (123-126) are imidazole-containing bromopyrrole alkaloids but, since in this case the imidazole ring is part of a histidine-like moiety, their 

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A novel Pd-catalyzed asymmetric annulation was reported between 5-bromopyrrole-2-carboxylate esters and vinyl aziridines <07OL2357>. The resulting pyrrolopiperazinones such as 58 served as key intermediates in the enantioselective synthesis of longamide B and a number of other pyrrole alkaloids. 

Benzosceptrins A-C are other dimeric bromopyrrole alkaloids with a unique benzo-cyclobutane moiety. Benzo-sceptrin A was isolated from a Halichondrid sponge of the genus Phakellia collected around Solomon Islands, and benzosceptrins B and C were isolated from a New Caledonian and a Japanese (Okinawa) Agelas sp. (Appenzeller et al, 2009 Kubota et al, 2009). 

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