Plants have been used as medicines for centuries, according to folklore, often without any perceptible efficacy. Plant materials were processed for medicinal use by chopping and grinding into powders or through aqueous extraction to make teas, smoking, or chewing. Often mixtures of plant products were combined ostensibly to create the most beneficial medicines. While the majority of these products were not effective, it was an accepted practice, and other than faith healing there was no real alternative.
Despite the difficulties encountered by administering mixtures of plant products in these crude preparations, several have yielded medicinally useful products upon purification. Opium, a dried concentrate of the milky latex derived from the poppy, P. somniferum, has been used for thousands of years as an analgesic. Recreational smoking of opium for its euphoric effect became popular in Europe in the early nineteenth century. Morphine (see Figure 6.1), which is the major active alkaloid in opium, is a powerful pain medicine, but owing to its addictive properties, it is mainly prescribed for the management of pain in terminal illnesses.
Malaria is an infectious disease caused by protozoan parasites of the genus Plasmodium. Symptoms of malaria have been treated with a number of plant preparations. Cinchona bark was originally discovered to have antimalarial properties in South America in the early 1600s and was soon imported to Europe where it was widely prescribed. Chemical investigations in the early 1800s by Pelletier and others led to the isolation of purified alkaloids possessing the antimalarial properties of the plant materials. Quinine (Figure 6.1), the major active principle obtained in this work, soon became the preferred treatment for symptoms of malaria and was manufactured through large-scale isolation from the bark. The advent of substituting purified chemicals for crude
plant preparations marked a turning point for pharmaceutical discovery. Quinine continues to have practical use in the treatment of certain resistant forms of P. falciperum.
In Chinese traditional medicine Artemisia annua or qinghao, has been employed as an antimalarial agent for many centuries. In this case, the sesquiterpene lactone artemisinin (Figure 6.1), containing a rare peroxide bridge, was isolated from the plant material and shown to possess effective antimalarial activity. Owing to the development of resistance to synthetic antimalarial drugs, artemisinin has become an effective alternative therapy. The yield of artemisinin in A. annua is relatively low making its commercial production an expensive process. Considering that the majority of people suffering from malaria live in underdeveloped regions of the world, a practical and cost-effective method for the production of artemisinin is highly desirable. This situation is a prime example of what has become known as the "supply issue" for the practical production of natural products. The issue is focused on the difficulty of producing commercial quantities of complex natural products.
Herbal remedies continue to play a significant role in human medicine. Chemical investigations have identified many of the active principles in many commonly used products. These products are often sold as dietary supplements rather than ethical pharmaceutical products. Because these products are complex mixtures of many natural products there is a need to establish criteria for their standardization. This situation is complicated by the natural variation in secondary metabolites produced by closely related species of medicinal plants. Owing to the possibility that variations in the composition of the products will result in unpredictable potency, the herbal products industry has been developing quality control standards. Black cohosh, for example, which is taken for the relief of menopausal symptoms, has a number of signature triterpenoid constituents including, actein, 23-epi-26-deoxyactein, and cimigenol-3-O-arabinoside (Figure 6.2). These compounds can be identified by coupled high-performance liquid chromatography-mass spectrometry (HPLC/MS), in comparison with authentic reference compounds. Our ability to quantify the amount of the key constituents in these herbal products will facilitate a better understanding of their efficacy and permit greater confidence in their use in medicine.
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