Amphidinol C, a major polyketide from an Irish strain of the dinoflagellate Amphidinium carterae

An Irish strain of the dinoflagellate Amphidinium carterae was previously shown to produce antibacterial amphidinol derivatives of unknown masses. Inspection of the major metabolites present in a bulk culture of this strain led to the isolation and structure elucidation of a new amphidinol derivative named amphidinol C featuring an unprecedented tetrahydropyran ring between the positions C-7 and C-11. The structure was determined using extensive analyses of NMR and MS data and comparison with data of analogues. The new ring was proposed to stem from a nucleophilic substitution of the sulphate present on the side chain of Amphidinol B. The major metabolites isolated were tested for their antibacterial and antifungal activities and Amphidinol C showed moderate fungicidal activity against yeast and filamentous fungi at 8–16 µg mL⁻¹.