1. Institute for Chemical Research, Kyoto University, Uji, Kyoto 611, Japan
2. Faculty of Fisheries, Kagoshima University, 4–50‐20 Shimoarata, Kagoshima 890, Japan
3. Faculty of Liberal Arts and Education, Shiga University, Otsu, Shiga 520, Japan
4. Department of Chemistry, Faculty of Science, Kochi University, Akebono‐cho, Kochi 780, Japan