Lissodendrins A and B: 2-Amino­imidazole Alkaloids from the Marine Sponge Lissodendoryx (Acanthodoryx) fibrosa

Chemical investigatio n of the Indonesian sponge Lissodendoryx (Acanthodoryx) fibrosa yielded the new 2‐aminoimidazole alkaloids lissodendrins A (1) and B (2). Their structures were unambiguously determined by extensive NMR spectroscopic (1H, 13C, ROESY and long‐range HMBC) studies and mass spectrometric (HRESIMS/MS) data. Lissodendrins A (1) and B (2) possess unprecedented skeletons with the latter compound bearing a (p‐hydroxyphenyl)glyoxal moiety, which is rarely encountered in natural products. A plausible biosynthetic pathway for these new metabolites is proposed. Two new 2‐aminoimidazole alkaloids, lisodendrins A and B, were isolated from the EtOAc extract of the sponge Lissodendoryx (Acanthodoryx) fibrosa collected in Indonesia. Lissodendrins A and B possess unprecedented skeletons, and the long‐range HMBC NMR experiment proved to be a valuable tool for establishing the structures of these compounds. A rationale for the biosynthesis of the new metabolites is likewise discussed.