Preface

Natural product chemistry covers various aspects of research into compounds from different plant, animal and microbial sources: their analysis, isolation, biological and pharmacological activities. In the 2003 Natural Product Chemistry issue of Current Organic Chemistry, there are five contributions which illustrate this diversity. The first refers to a survey of phytohormones. As their name implies, these hormones are of plant origin and they can take the form of different classes of chemical compound: isoflavones, lignans, coumestans and stilbenes. They are found in numerous foodstuffs (one source being soy products) and can reduce the incidence of gynecological cancers, cardiovascular diseases and osteoporosis in postmenopausal women Certain human estrogens and androgens are also found in small amounts in plants. Another article on bioactive compounds, by Cos, Vanden Berghe, De Bruyne and Vlietinck, reviews the latest developments in natural products used as antiviral agents. In the treatment of viral infections, there are problems of tolerance and drug resistance associated with the existing drugs. For this reason, the demand for new antiviral agents is high. The emphasis is given to plant-derived substances with anti-human immunodeficiency virus (anti-HIV) activity, with special reference to their mechanisms of action. Compounds with anti-herpes simplex virus (anti-HSV) are similarly listed: these include alkaloids, carbohydrates, flavonoids, lignans, tannins, terpenes and proteins. The third contribution is a more specialized review on the occurrence of brominated diterpenes from marine organisms, by Kornprobst and Al-Easa. These have only been found in red algae and gastropods but they give rise to a great diversity of different structures. Some of these have biological activities, including cytotoxicity and antimicrobial properties. Their spectroscopic data and biogenetic relationships are also presented. Finally, two articles describe the synthesis of bioactive natural products and their derivatives. Morzycki and co-workers report efforts directed towards the synthesis of cytostatic natural products. The first two classes, the cephalostatins and the ritterazines, are found in marine organisms and belong to the family of trisdecacyclic pyrazines, consisting of two steroid units. Cephalostatin 1 notably shows considerably higher antitumour activity than currently used chemotherapeutics. The other group of active compounds is found in the bulbs of Ornithogalum saundersiae (Liliaceae) and consists of cholestane glycosides. Barua and co-workers summarize synthetic work on 1,2,4-trioxane-type artemisinin analogues. Artemisinin, a sesquiterpene lactone from the Chinese plant Artemisia annua (Asteraceae), is a very effective antimalarial compound which is important for the treatment of patients affected by resistant strains of the parasite. The 1,2,4-trioxane ring system is essential for the activity of artemisinin and hence much synthetic work involves the production of analogues with this structural feature. I would like to express my sincere thanks to all contributors in this volume for the excellent reviews of natural product research that they have produced.