1. Centre for Pharmacognosy and Phytotherapy, and Department of Pharmaceutical and Biological Chemistry, The School of Pharmacy, University of London, 29/39 Brunswick Square, London WC1N 1AX, U.K., Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1 7HT, U.K, and School of Pharmacy, University of Bradford, West Yorkshire BD7 1DP, U.K.