1. Department of Neuroscience and Medical Research Institute, College of Medicine, Ewha Womans University, Ewha Global Challenge BK21, Seoul 158-710, South Korea
2. Union Chemical Corporation, Cheongju 361-290, Chungbuk, South Korea
3. Department of Chemistry, Institute for Basic Sciences, College of Natural Sciences, Chungbuk National University, Cheongju 361-763, Chungbuk, South Korea