Symbioimine and neosymbioimine, amphoteric iminium metabolites from the symbiotic marine dinoflagellate Symbiodinium sp. Original Research Article

Two amphoteric iminium metabolites, symbioimine (1) and neosymbioimine (2), were isolated from a cultivated symbiotic marine dinoflagellate Symbiodinium sp. Compounds 1 and 2 have a characteristic 6,6,6-tricyclic iminium ring structure and an aryl sulfate moiety. The plausible biogenetic pathway of 1 and 2 can be explained by an intramolecular Diels–Alder reaction followed by imine cyclization. Symbioimine (1) inhibited the differentiation of RAW264 cells into osteoclasts (EC50 = 44 μM), and significantly inhibited cyclooxygenase-2 activity at 10 μM. Thus, symbioimine is a potent anti-resorptive and anti-inflammatory drug.