Isolation of Thuridillins D–F, Diterpene Metabolites from the Australian Sacoglossan Mollusk Thuridilla splendens; Relative Configuration of the Epoxylactone Ring

This first chemical study of the sacoglossan mollusk Thuridilla splendens from Mooloolaba, South East Queensland, has resulted in the isolation of three new metabolites, thuridillins D–F (1–3), and one known metabolite, thuridillin A (4). Thuridillin D (1) was isolated by conventional flash chromatography on silica gel, while a mixture of thuridillins E (2) and F (3) was obtained by PTLC on AgNO3-impregnated silica gel. Thuridillins D–F were determined to be structurally related to thuridillin B (5); 1 possessed a hydroxy group at C-11, and 2 and 3 were Δ10,11- and Δ11,12-isomers, respectively. HSQC-HECADE NMR data, together with conformational analysis, NOESY experiments, and 1H–1H coupling studies enabled assignment of the individual relative configurations of the epoxylactone, the 2,5-diacetoxy-2,5-dihydrofuran, and cyclohexyl moieties within thuridillin D (1).