1. College of Pharmacy, Seoul National University, San 56-1, Shilim, Kwanak, Seoul 151-742, Korea, Natural Products Research Institute, College of Pharmacy, Seoul National University, 28 Yungun, Jongro, Seoul 110-460 Korea, and College of Pharmacy, Ewha Womans University, 11-1 Daehyun, Seodaemun, Seoul 120-750, Korea