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.

We determined the ensemble of conformations and therelative configuration of dibromopalau'amine by using NMR parameters such as 3J couplings, ROEs and residual dipolar couplings. Based on the ensemble electronic circular dichroism (ECD) and optical rotatory dispersion (ORD) spectra were calculated using DFT and compared to experiment. By this method the absolute configuration of natural (–)‐dibromopalau'amine was determined as 6S,10R,11S,12S,16R,17S,18S,20S.

In addition to the four known stylissamides, A (1), B (2), C, and D, two new cyclic heptapeptides, stylissamides E (3) and F (4), were isolated from the Caribbean sponge Stylissa caribica. The structures of 3 and 4 were elucidated from a combination of mass spectrometric and NMR spectroscopic data as cyclo-(cis-Pro(1)-Tyr(2)-trans-Pro(3)-Ala(4)-Ile(5)-Gln(6)-Ile(7)) for stylissamide E (3) and cyclo-(trans-Pro(1)-cis-Pro(2)-Phe(3)-Asp(4)-trans-Pro(5)-Arg(6)-Phe(7)) for stylissamide F (4).

No abstract

Two new haliclamines were identified directly from the crude extract of the Arctic sponge Haliclona viscosa using improved chromatographic conditions and a detailed knowledge about the fragmentation pattern of haliclamines. These are haliclamine G (1) with two alkyl chains of equal length (10 methylene groups) and haliclamine H (2) with alkyl chains of 10 and 12 methylene groups. Due to the limited amount of sponge material available, the haliclamines were not isolated, and the structure elucidation relied on the chromatographic and mass spectrometric comparison with synthetic compounds.

No abstract

Two new haliclamines (I) are identified directly from the crude extract of an arctic sponge using improved chromatographic conditions and detailed knowledge about the fragmentation pattern of haliclamines. -(CYCHON, C.; SCHMIDT, G.; MORDHORST, T.; KOECK*, M.; Z. Naturforsch., B: Chem. Sci. 67 (2012) 9, 944-950, http://dx.doi.org/10.5560/znb.2012-0039 ; Alfred-Wegener-Inst. Polar Meeresforsch., D-27570 Bremerhaven, Germany; Eng.) -M. Paetzel 05-159