March, 2002: Thailand
Insects are our greatest competition for food. In the United States alone, billions of dollars of crop plants are lost annually to insect damage. Additionally, livestock are affected by insects, which often cause animals' health to deteriorate and can sometimes render them unsafe for consumption. Therefore, the production of effective insecticidal compounds is of great economic importance. Furthermore, since companion animals such as dogs and cats are also affected by ectoparasites (parasites found on the animal as opposed to within the body), concern is paramount that insecticides be environmentally friendly and have low toxicity.
Recently, researchers at Merck Research Laboratories in Rahway, New Jersey, isolated a chemical compound from a plant that has been especially effective against fleas, ticks, and mosquito larvae. The compound, which comes from the root of Trigonostemon reidioides, was collected in Thailand by botanists from The New York Botanical Garden. This finding is an example of the expedient and promising information that can result from collaboration between a pharmaceutical company and a botanical garden. Extracts produced from T. reidioides are currently undergoing further research for agricultural and livestock applications.
 Euphorbia, a succulent plant in Euphorbiaceae, demonstrates the diversity of plants in this family. |
The plant samples were collected in the Rat Buri Province of Thailand, a country in Southeast Asia. Although the stems, leaves, and wood of T. reidioides were tested, the active ingredient was found to be most concentrated within the roots of the plant. T. reidioides is in the Euphorbiaceae family, commonly known as the spurge family. Euphorbiaceae is a highly diverse family represented by about 313 genera and 8,100 species, including trees, shrubs, herbs, vines, and succulent, cactuslike members. This family of dicots tends to house a white, often irritant latex in specialized cells throughout the plant body. Included among the many economically valuable genera within Euphorbiaceae are Euphorbia sp., the poinsettias; Hevea sp., the rubber tree; and Manihot sp., which yields cassava, tapioca, and arrowroot starch.
 Chemical structure of rediocide A. |
After isolating the active ingredient from the roots, scientists faced the task of structural elucidation-finding out what the chemical looked like. Using several analytical tools, such as HPLC (high-pressure liquid chromatography), GC (gas chromatography), and NMR (nuclear magnetic resonance), the scientists worked like detectives to put together the pieces of a chemical puzzle. Not only was the active ingredient mapped out, but a novel compound was elucidated. This was good news because it meant that, to date, no one had published research identifying the chemical they now had in front of them; therefore, no one else had discovered its insecticidal properties either! Eventually, the chemical was named rediocide A, after the species epitaph. It was determined to have a molecular formula of C44H588O13 and a molecular weight of 795.3955.
Rediocide A was tested at the Merck facilities and showed potent activity against mosquito larvae in biological assays. It was also shown to be highly effective against fleas, specifically Ctenocephalides felis, the pest of domesticated animals. But even more exciting than the insecticidal properties was the finding that these effects can be achieved at extremely low doses-for example, 0.25 ppm, compared to other products, which require 10+ ppm to invoke similar insecticidal results. Merck claims that rediocide A is one of the most powerful anti-flea compounds discovered to date within their research programs.
References, Websites, and Further Reading
Jayasuriya, H., et al. 2000. Structure and stereochemistry of rediocide A, a highly modified daphnane from Trigonostemon reidioides exhibiting potent insecticidal activity. Journal of American Chemical Society 122(20), pp. 4998-99.
Kokpol, U., et al. 1990. Structure of trigonostemone, a new phenanthrenone from the Thai plant Trigonostemon reidioides. Journal of Natural Products 53, p. 1148.
Powerful flea killer isolated from plant. May 29, 2000. Chemical & Engineering News 78(22).
http://encarta.msn.com
"Thailand," Microsoft Encarta Online Encyclopedia 2001
www.nybg.org
The New York Botanical Garden website
Related Reading in Stern, Kingsley R. 2000. Introductory Plant Biology,
8th ed. New York: McGraw-Hill Companies.
Chapter 5: Roots and Soils, pp. 63-80
Chapter 6: Stems, pp. 83-102
Wood and Its Uses, pp. 99-102
Chapter 8: Flowers, Fruits, and Seeds
Differences between monocots and dicots, pp. 129-30; table 8.1
Chapter 24: Flowering Plants and Civilization
Euphorbiaceae, pp. 444-47
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