Ethnobotany: The Chemist's Source for the Identification of Useful Natural Products Denise M. Hosler and Michael A. Mikii' University of Colorado at Denver, Denver, CO 80202 Isolation of secondary plant metaholites constitutes a chemical research proiect with significant potential for future benefits to mankind. ~ h o s e n c a r e f u l l ~ ;plant a is likely to possess novel structures potentially beneficial in areas of pharmacology ( I ) , agriculture (2), or chemotaxonomy (3). The selection of a plant for investigation by a natural product chemist is the most critical. vet often least understood. step in this process. This paper details the various approach: es a novice can utilize in the selection of notentiah useful plants for study, as well as the correct steps to he taken for the plant's procurement, and a brief review of analysis. While the focus of this paper concentrates on the pharmacological aspects of such studies, the procedures outlined are appropriate for phytochemical analyses regardless of the plant's ultimate area of chemical value. Background The olant kinedom is a virtual eoldmine of new chemical compohds waiiing to be discov;?red. The U.S. Office of Technology Assessment (OTA) recently estimated that, while there are 500,000 to 750,000 species of higher plants on earth, no more than 10%have been examined for their chemical constituents (2).Their survey of current pharmaceutical use, however, revealed that of the total prescription drugs dispensed, 25% are plant-derived. In the US. during 1980, the retail value of prescriptions containing active compounds from higher plants was estimated to be at least $8 billion, and of over-the-counter drugs containing such compounds, $1 billion. Additionally, chemical syntheses of most of the pure plant compounds used in prescriptions are either technically or economically infeasible; therefore, most are still extracted from plants. Ultimately, plant constituents may be isolated and nsed directly as therapeuticagents, or as starting materials for drug synthesis, or they may serve as models for pharmacologically active compounds in drug synthesis. Well-known examples include digitoxin, morphine, atropine, penicillin, coumarins, and colchicioe (3). During the '60's, Eli Lilly isolated, purified, and marketed alkaloids from Catharanthus roseus (L.) G. Don. (Madagascar periwinkle), which yielded two successful anticancer drugs, vincristine and vinblastine (2). The structures of these two metaholites, as well as all other specific plant products discussed in this paper, are illustrated in Figure 1. Plant compounds are also heing used as natural insecticides and show promise in agriculture and industrial feedstocks. with the added benefit that plant-derived hiocides are biodegnidahle (2'). The imporrant ecological rule of secondary plant tneraholiteli 1s that of defense against ohvtovhagons&ects and pathogens (4). In 1979, steelink and ~ a r shall isolated chromene and benzofuran compounds, such as encecalol and encecalin from Encelia farnoin Gray (brittle bush). They had originally investigated this plant due to its reported use as an analgesic chewing gum and incense by the
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Author to whom correspondence should be addressed. Presented before the Chemical Education Division at the 192nd National Meeting 10, 1986, Anaheim, of the American Chemical Society, . SeDtember . CA. 328
Journal of Chemical Education
Arizona Indians (5). Later experiments by Rodriguez with Encelia chromenes and benzofurans revealed that these chemicals are insect antifeedents and exhibit antiiuvenile activity when applied topically. Phytochemists heGeve the desert allelochemicals may he of considerable importance in controlling insect pests of crop plants (4). Phytolacca dodecandra L'Herit (endod), which has been nsed by African natives as a detergent, &found to kill snails downstream. In a pilot study conducted in Ethiopia, the use of endod as a mol
