1. Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand, Plant Extracts Research Unit, New Zealand Institute for Crop & Food Research Limited, Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand, and Department of Herbal Resources, Professional Graduate School of Oriental Medicine, Wongkwang University, Iksan 570-749, Korea