Biological activities from medicinal plants

CHEMISTRY AND BIOLOGICAL ACTIVITIES OF ISOPRENYLATED FLAVONOIDS FROM MEDICINAL PLANTS (MORACEOUS PLANTS AND GLYCYRRHIZA SPECIES)... 

Structure and Biological Activity of Triterpenoids and Aromatic Compounds from Medicinal Plants... 

In this chapter part of our recent work on the chemistry and biological activity of metabolites from medicinal plants will be summarized. 

S Nishibe. Structural elucidation and biological activities of phenylpropanoids, cou-marins and lignans from medicinal plants. In AU Rahman, ed. Studies in Natural Products Chemistry, vol. 5. Structure Elucidation (Part B). Amsterdam Elsevier, 1989, pp. 505-548. 

Lignans, which are main area of our concern in this article, are distributed widely in the plant kingdom. Many biologically active lignans are isolated from medicinal plants. A number of reviews about total syntheses and biological activities have been reported (ref. 2). 

Isolation, Characterization, and Biological Activities of Polysaccharides from Medicinal Plants and Mushrooms... 

It would not be too far fetched to state that life on this planet is totally dependent on two compounds based on the purine nucleus. Two of the bases crucial to the function of DNA and flNA—guanine and adenine—are in fact substituted purines. It is thus paradoxical that the lead for the development of medicinal agents based on this nucleus actually came from observations of the biologic activity of plant alkaloids containing that heterocyclic system, rather than from basic biochemistry. 

Many new drugs are discovered by studying the properties of compounds found in plants or other materials that have been used as medicines for centuries (Fig. F. 1). Once chemists have extracted a biologically active compound from a natural product, they identify its molecular structure so that it can be manufactured. This section focuses on the first step in identifying the molecular structure, the determination of the empirical and molecular formulas of the compound. 

According to Julsing et al. [2], alkaloids can be classified in terms of their biological activities, their chemical structures, or their biosynthetic pathways [2]. Over 12 000 alkaloids are known so far from plants, and several of these are being used medicinally in the global pharmaceutical market worth 4 billion US dollars [2]. 

Chlorinated taxodione 8 was also found along with taxodione 1 from the stem of Rosemarinus officinalis, although its biological activity is yet to be studied (Scheme 8.2).21 Maytenoquinone 9, a structural isomer of taxodione 1, has been isolated from the roots of several medicinal plants such as Maytenus dispermus,22 Salvia melissodora,23 and Harpagophytum procumbems (devil s claw)24 used in folklore medicine. 

Page JE, Balza F, Nishida T, Towers GH. (1992). Biologically active diterpenes from Aspilia mossambicensis, a chimpanzee medicinal plant. Phytochemistry. 31(10) 3437-39. 

Finally, researchers may use an ethnohotamcal approach, that is, one that focuses on medicinal plants that have traditionally heen used in various cultures. The assumption underlying this approach is that plants on which people have relied for medicines in the past may very well contain biologically active chemicals that can be either isolated, purihed, and used as drugs or used as models from which biologically active analogs can he produced. 

The base-catalysed racemization of the alkaloid (-)-hy oscy amine to ( )-hyoscyamine (atropine) is an example of enolate anion participation. Alkaloids are normally extracted from plants by using base, thus liberating the free alkaloid bases from salt combinations. (—)-Hyoscyamine is found in belladonna Atropa belladonna) and stramonium Datura stramonium) and is used medicinally as an anticholinergic. It competes with acetylcholine for the muscarinic site of the parasympathetic nervous system, thus preventing the passage of nerve impulses. However, with careless extraction using too much base the product isolated is atropine, which has only half the biological activity of (—)-hyoscyamine, since the enantiomer (+)-hyoscyamine is essentially inactive. 

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