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■ Oscillatoxin E and Its C7 Epimer Show Distinct Growth Inhibition Profiles against Several Cancer Cell Lines

Yusuke Hanaki,* Yusuke Araki, Toshio Nishikawa, and Ryo C. Yanagita

*Faculty of Agriculture, Kagawa University, Kagawa 761-0795, Japan

Abstract

Oscillatoxins (OTXs) are naturally occurring polyketides produced by some marine cyanobacteria. We have recently reported the total synthesis and in vitro biological activities of OTX-D, E, and F. Their spiro-ether structure was synthesized with an intramolecular Mukaiyama aldol reaction as a key step. Although the desired isomer was stereoselectively obtained, some amount of its C7 epimer was also produced as a byproduct. Using the C7 epimer, we investigated the effect of stereochemistry at the spiro-center of OTX-E (1) on its antiproliferative activity against several cancer cell lines. Growth inhibitory activity of 1 and its C7 epimer 2 was not strong, but they showed different efficacy profiles from each other. This result suggests that our synthetic method for OTXs would contribute to not only total synthesis of natural products but also to construction of chemical libraries containing unique biologically active compounds.