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Over the past few years, increasing attention has been paid to the search for bioactive compounds from natural sources. The success of plant-derived products such as paclitaxel (Taxol) in tumor therapy or artemisinin in the treatment of malaria has provided the impetus for the introduction of numerous research programmes, especially in Industry. A great deal of effort is being expended in the generation of novel lead molecules of vegetable, marine and microbial origin by the use of high throughput screening protocols. When interesting hits are found, it is essen­ tial to have methods available for the rapid isolation of target compounds. For this reason, both industry and academia need efficient preparative chromatographic separation techniques and experience in their application. Purified natural products are required for complete spectro­ scopic identification and full characterization of new compo­ unds, for biological testing and for the supply of pharmaceuti­ cals, standards, and starting materials for synthetic work. Obtaining pure products from an extract can be a very long, te­ dious and expensive undertaking, involving many steps. Sometimes only minute amounts of the desired compounds are at hand and these entities may be labile. Thus it is an advantage to have access to as many different methods as possible in order to aid the isolation process. Although a certain amount of trial and error may be involved, nowadays there is the possibility of devising suitable rapid separation schemes by a judicious choice of the different techniques available.

Over the last few years several new instrumental techniques have been introduced for chromatographie separations. In addition, rapid developments in existing methods, such as preparative HPLC, have taken place. Despite these advances, how­ ever, a handbook covering the various preparative aspects ofthe new separation tech­ niques does not exist. This book is an attempt to fill the gap and to present a compila­ tion of modern separation techniques that will be useful for researchers faced with day-to-day preparative problems. Numerous examples of separations have been selected in order to show the possibilities (and also the limits) of each technique treated. These are often either applications from our own laboratory or else they reflect the approach we have been following for the isolation of natural products from plant sourees. Owing to the large number of published papers and the diversity of secondary plant constituents. an exhaustive survey of the literature has not been undertaken. We hope, however, that the examples selected will suggest to the reader which technique(s) and which conditions to choose for a particular isolation problem in the field of natural products. For invaluable help in the preparation of the manuscript for this book, we would like to thank Corinne Appolonia and Christine Marston. Lausanne, November 1985 K. Hostettmann M. Hostettmann A.. Marston Foreword Although not many people realize this, isolation and purification of biologically active materials is becoming increasingly crucial.