1. Department of Molecular Science and Technology, Graduate School of Engineering Sciences, Kyushu University, 6‐1 Kasuga‐kohen, Kasuga‐shi, Fukuoka 816, Japan
2. Institute of Advanced Material Study, Kyushu University, 6‐1 Kasuga‐kohen, Kasuga‐shi, Fukuoka 816, Japan
3. Laboratory of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Coimbrac, 3000 Coimbra, Portugal