1. The authors thank Dr. T. Hoshino (Mukaishima Marine Biological Station, Hiroshima University) for his kind identification of the marine sponge, Prof. T. Miyazawa, Mr K. Wakamatsu and Dr T. Higashijima for the NMR measurement, Mr Z. Nagahama for his assistance in collecting the marine sponge, and Miss M. Hamashima of this institute for her technical assistance.
2. Kobayashi, J., Ohizumi, Y., Nakamura, H., Yamakado, T., Matsuzaki, T., and Hirata, Y., Experientia39 (1983) 67.
3. Kobayashi, J., Nakamura, H., Ohizumi, Y., and Hirata, Y., Tetrahedron lett.27 (1986) 1191.
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