Synthetic Studies of Marine Polyketide Ascospiroketal including 5, 5-Spiroketal Moiety

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Ascospiroketal A is a marine polyketide having specific tricyclic skeleton including tetrahydrofuran and 5,5-spiroketal.Sufone derivative, segment C7-C11, was synthesized from D-(+)-malic acid by 9 steps. Alkyl iodide derivative, segment C1-C6, was synthesized from L-(+)-tartaric acid by 12 steps. 5,5-Spiroketal segment was synthesized by combination of segment C7-C11 and segment C1-C6 and then the removal of 1,3-dithiane and the protecting group of hydroxy groups. Synthesis of tricyclic segment including tetrahydrofuran ring was successfully carried out by construction of quaternary asymmetric carbon and intramolecular etherification. Total synthesis of ascospiroketal A is currently under way by connection of the tricyclic segment and C12-C16 segment.