Richard Synge (1970) - Proteins and Poisons in Plants

Richard Synge (1970)

Proteins and Poisons in Plants

Richard Synge (1970)

Proteins and Poisons in Plants

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The 1952 Nobel Prize in Chemistry was awarded to two British chemists: Archer Martin and Richard Synge. They had jointly discovered partition chromatography, a technique for separating compounds based on the partition between a liquid stationary phase, which is immobilized by attachment to a solid carrier, and a liquid or gaseous mobile phase. This was a ground-breaking contribution, which led to the development of important modern analytical techniques like gas chromatography.Synge’s efforts with respect to partition chromatography stemmed from his interest in amino acids and proteins. Consequently, he begins the present lecture with a few general remarks on these compound classes, but then takes a rather sharp turn towards the fields of plant toxins. He mentions that, since plants cannot attack, run away or hide, there has been evolutionary pressure to develop chemical means of keeping the number of predators down. This pressure, Synge says, has led to a fantastic variety of plant toxins, a “galaxy of organic compounds”. Some of its more prominent representatives are the alkaloids caffeine, morphine, cocaine and nicotine, for example. Synge then embarks on an interesting journey through some particular examples of plant toxins, beginning with those which belong to the group of proteins. A very well-known representative of this group is ricin, which is found in the castor oil plant. Ricin, one of the most potent toxins known, inhibits protein synthesis and causes death by paralysis of vital organs. While, like all proteins, ricin has to be made from valuable nutrients, other plants have found a more economical way of becoming toxic: the accumulation of toxic elements like selenium and fluorine from soil. Synge mentions the African plant Dichapetalum, which builds up fluoroacetic acid. The latter disrupts the citric acid cycle, halting cellular energy metabolism, leading to altered blood pressure, heart failure and death. Today (2013), the compound is used for mammalian pest control in several countries, particularly in Oceania.Synge eventually also discusses the polyphenols, a class of compounds known for its antioxidant properties. Today, certain polyphenols are marketed as nutritional supplements in the context of anti-ageing. However, polyphenols also play an important role in soil formation and maintenance, as Synge points out. Polyphenols originating from decaying plants are the precursors to humic acids, which represent the main organic constituents of soil. There, they form important reservoirs of nitrogen and sulfur and retain water as well as certain metals, Synge explains. In closing his talk, he gives some insight into the discovery processes of natural products like plant toxins, mentioning that until a few years before his talk, the isolation and characterization of a single natural product required the work equivalent of an entire PhD thesis (usually between 3 to 5 years). With respect to emerging analytical techniques like organic mass spectrometry and x-ray crystallography, Synge expected a significant reduction of this timeframe. And he was not mistaken. Since his talk a range of new developments have been made and a significant boost in the rate of natural product discovery could be achieved. Some of these developments, i.e. nuclear magnetic resonance spectroscopy and the electrospray ionization technique, led to the 2002 Nobel Prizes in Chemistry, which was awarded “for the development of methods for identification and structure analyses of biological macromolecules". That such developments were badly needed is illustrated by the extreme case of bombykol, the sex pheromone of the female silk moth. It took its discoverer, 1939 Chemistry Laureate Adolf Butenandt, more than 20 years to isolate and characterize the compound. The complete story can be heard in his 1960 Lindau lecture (LINK).David Siegel

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