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The chemistry of the burrowing sponge Aka coralliphagum was investigated to identify chemically labile secondary metabolites. The HPLC-MS analysis of the two growth forms typica and incrustans revealed different metabolites. The previously unknown sulfated compounds siphonodictyals B1 to B3 (6-8), corallidictyals C (9) and D (10), and siphonodictyal G (11) were isolated, and their structures were elucidated by NMR and MS experiments. The compounds were tested in a DPPH assay, in antimicrobial assays against bacteria, yeasts, and fungi, and in antiproliferation assays using cultures of mouse fibroblasts. The biological activity was linked to the presence of the ortho-hydroquinone moiety.The burrowing sponge Aka coralliphagum ()Siphonodictyon coralliphagum) is a bright yellow colored sponge that burrows into corals. Four distinct morphological growth forms have been described for Aka coralliphagum from the Caribbean: forma typica, f. tubulosa, f. obruta, and f. incrustans. 1 Several bioactive sesquiterpene hydroquinones, such as the siphonodictyals (B, 1) and siphonodictyols, 2 were obtained from the forms tubulosa and typica. Although the isolation of labile compounds such as siphonodictyols G (2) and H (3) suggested the existence of additional sulfated phenolic compounds in A. coralliphagum, compounds such as the siphonodictyals were isolated without respect to the occurrence of sulfated metabolites. Past isolation and purification methods did not account for the problem of compound hydrolysis. 2a,b This paper describes the isolation, structure elucidation, and biological testing of the new, labile metabolites siphonodictyals B1 to B3 (6-8), corallidictyals C (9) and D (10), and siphonodictyal G (11) from the Aka growth form incrustans. In order to compare the secondary metabolites of the two growth forms incrustans and typica, an HPLC analysis of their crude extracts was performed. These two forms of Aka occur in different habitats, with typica predominating on shallow water reefs (10-15 m) while incrustans occurs on deep water vertical slopes (20-25 m). It was deemed important to isolate the labile natural products of these two growth forms in their naturally occurring forms in order to understand more about their biological and ecological function. Results and DiscussionExtracts of sponge samples were investigated by an HPLC-MS screening. The two growth forms of Aka coralliphagum (typica and incrustans) showed differences in HPLC fingerprints and their major metabolites (Figure 1). While forma typica contained more polar compounds (shorter retention times), forma incrustans contained three main compounds with a less polar character. Further characterization by HPLC-API-CID-MS/MS showed a single or double sulfation of compounds with shorter retention times. This was deduced by loss of m/z 80 under MS/MS conditions and detection of a [SO 3 ] -ion at m/z 80 (see Supporting Information) 3 as well as a sulfur-specific isotopic pattern. These results indicate that the two growth forms have considerable differences...

SummaryThe 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.

Two new bromopyrrole alkaloids were isolated from the Caribbean sponge Stylissa caribica. The new natural products, 4-bromopyrrole-2-carboxyarginine (1) and 4-bromopyrrole-2-carboxy-N(epsilon)-lysine (2), are derivatives of amino acids linked with a 4-bromopyrrole-2-carboxylic acid. The structures were elucidated on the basis of NMR and MS/MS data and their absolute configurations assigned via synthesis.

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