1. Natural Products Research Institute, College of Pharmacy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea, Department of Agricultural Environment, National Academy of Agricultural Science, Suwon 441-707, Republic of Korea, and Department of Agricultural Biotechnology, College of Agriculture and Life Science, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-921, Republic of Korea