Okadaic Acid, a Cytotoxic Polyether from Two Marine Sponges of the

Donna Van Engen and Jon Clardy*. Department of Chemistry-Baker ..... SOC. 1966, 88, 5044-5045. Green, M. L. H.; Ishaq, M.; Whiteley, R. N. J. Chem. SO...
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J. Am. Chem. SOC.1981, 103, 2469-2471 it has two spirofused six-membered ketal ring systems in place of the more commonly encountered spiroketal involving six- and fixe-membered rings. The presence of two fused tetrahydropyran rings (D, E) is also unique. Acanthifolicin exhibits ED5