Chemical defenses of the Caribbean sponges Agelas wiedenmayeri and Agelas conifera

Previous studies have determined that Caribbean reef sponges of the genus Agelas are chemically defended from fish predation by brominated pyrrole alkaloids, and that the compounds responsible for this defense have been elucidated for one species, Agelas clathrodes. In this study, we expand our understanding of chemical defense in this common sponge genus to include the characterization of defensive metabolites in the tissues of Agelas wiedenmayeri and Agelas conifera. Bioassay-directed isolation of defensive metabolites was undertaken using fish feeding assays carried out in laboratory aquaria and in the field. Agelas wiedenmayeri contained the same two major metabolites as Agelas clathrodes, 4,5-dibromopyrrole-2-carboxylic acid (1), and oroidin (2), in addition to a small amount of bromoageliferin (7). The two major metabolites were present at higher concentrations in samples of Agelas wiedenmayeri than in Agelas clathrodes, and their relative concentrations were reversed, with Agelas wiedenmayeri on average containing more 4,5-dibromopyrrole-2-carboxylic acid (1) (2.0 mg/mL) than oroidin (2) (0.8 mg/mL). Agelas conifera contained a mixture of dimeric bromopyrrole alkaloids dominated by sceptrin (3), with <10% each of dibromosceptrin (5), bromoageliferin (7), dibromoageliferin (8), ageliferin (6), and bromosceptrin (4). Mean concentration of sceptrin (3) in sponge tissue was 5.3 mg/mL; this compound deterred feeding of reef fish in aquarium assays at 1.0 mg/mL, the lowest concentration assayed. Sceptrin (3) concentrations were higher in sponges collected in the southern Bahama Islands than those collected in the middle Bahamas, but reasons for this variation remain unclear. The structure-activity relationship of the pyrrole group was investigated by assaying derivatives of the active metabolites. Feeding deterrent activity of the molecule was enhanced by the addition of bromine to the pyrrole group, but not affected by exchange of the heteroatom from N to O or S. Combining an understanding of the structure-activity relationship of Agelas metabolites with an understanding of the variation in these metabolites across the genus may provide insight into the evolution of defensive chemistry in this highly successful taxa of pan-tropical sponges

New bromopyrrole alkaloid from the marine sponge Agelas wiedenmayeri

A detailed analysis of the chemical constituents of a specimen of Agelas wiedenmayeri (Alcolado, 1984) was performed. Four brominated alkaloids (1-4) were isolated and one was identified as a new bromopyrrole metabolite. The structure of the new compound, 1, was assigned using spectroscopic methods. Compounds 2 and 3, which are the major brominated metabolites, have been previously described from other Agelas sponges. The new compound, 1, may be a biosynthetic precursor for oroidin-like derivatives

The marine sponge Agelas citrina as a source of the new pyrrole–imidazole alkaloids citrinamines A–D and N-methylagelongine

The chemical investigation of the Caribbean sponge Agelas citrina revealed four new pyrrole–imidazole alkaloids (PIAs), the citrinamines A–D (1–4) and the bromopyrrole alkaloid N-methylagelongine (5). All citrinamines are dimers of hymenidin (6) which was also isolated from this sponge as the major metabolite. Citrinamines A (1) and B (2) are derivatives of the PIA dimer mauritiamine (7), whereas citrinamine C (3) is derived from the PIA dimer nagelamide B (8). Citrinamine D (4) shows an uncommon linkage between the imidazole rings of both monomeric units as it is only observed in the benzocyclobutane ring moiety of benzosceptrins A–C (9–11). Compound 5 is the N-methyl derivative of agelongine (12) which consist of a pyridinium ring and an ester linkage instead of the aminoimidazole moiety and the common amide bond in PIAs

Multiple defensive roles for bromopyrrole alkaloids from Caribbean Agelas sponges. Proceedings of the 6th International Sponge Conference, Rapallo, Italy, 2002

Previous studies have indicated that Caribbean reef sponges of the common genus Agelas are chemically defended from fish predators by brominated pyrrole alkaloids: Agelas clathrodes and A. wiedenmayeri by 4,5-dibromopyrrole-2-carboxylic acid (1) and oroidin (2), A. conifera by sceptrin (3). In this study, we expand our understanding of chemical defense in this sponge genus to include an extensive HPLC quantification analysis of the defensive metabolites in tissues of A. cerebrum, A. cervicornis, A. dilatata, A. dispar and A. sceptrum. A. cervicornis and A. dispar contained the same two major metabolites as A. clathrodes and A. wiedenmayeri, while A. cerebrum, A. dilatata and A. sceptrum contained a mixture of dimeric bromopyrrole alkaloids dominated by sceptrin, similar to A. conifera. At natural volumetric concentrations, both crude extracts and purified compounds from each species were unpalatable to a common generalist reef fish, Thalassoma bifasciatum, in aquarium assays, and inhibited attachment of the marine bacterium Vibrio harveyi in surface fouling assays. Brominated pyrrole alkaloids may play multiple ecological roles in protecting sponges of the genus Agelas