1. Laboratory of Medicinal Chemistry, College of Pharmacy, Ewha Womans University, Seoul 120-750, Korea, College of Pharmacy, Seoul National University, Seoul 151-742, Korea, Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes, and Digestive and Kidney Disease, National Institute of Health, Bethesda, Maryland 20892, and College of Pharmacy, Pusan National University, Pusan 609-753, Korea