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Environment

ACS Award For Team Innovation

Sponsored by ACS Corporation Associates

by Kenneth Moore
February 15, 2010 | A version of this story appeared in Volume 88, Issue 7

Stevenson
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Credit: Sheldon Sumpter (All)
Credit: Sheldon Sumpter (All)

Bringing any product to market is a daunting challenge that takes dedication from all involved, but bringing to market an entirely new class of insecticides with high potency and target selectivity is even more challenging. DuPont Crop Protection’s Thomas M. Stevenson, Thomas P. Selby, John H. Freudenberger, and Daniel Cordova—the scientists whose discovery led to the development and commercialization of Rynaxypyr (chlorantraniliprole), a broad-spectrum anthranilic diamide insecticide with a novel mode of action and low nontarget toxicity—felt the exhilaration of meeting that challenge.

Selby
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Credit: Sheldon Sumpter (All)
Credit: Sheldon Sumpter (All)
Freudenberger
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Credit: Sheldon Sumpter (All)
Credit: Sheldon Sumpter (All)
Cordova
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Credit: Sheldon Sumpter (All)
Credit: Sheldon Sumpter (All)

“In the field of crop protection, discovery of a new chemical class that provides commercial control and has a novel mode of action happens only once or twice in the time-span of one’s career,” Cordova says. “I feel extremely fortunate.”

The scientists collaborated and worked diligently, leading Rynaxypyr to market in 2007, less than a decade after project leader George P. Lahm discovered anthranilic diamides, a novel class of insecticidal chemistry, in 1999. In the first two years, more than 2,000 compounds were synthesized and evaluated and structure-activity relationships were refined. This led to a 1,000-fold improvement in potency over the original lead compounds, says William E. Barnette, research manager of Discovery Chemistry at DuPont Crop Protection.

Selby’s work contributed the first heterocyclic analogs, including the first pyrazoles, and the critical 1,3,5-substitution pattern. Freudenberger developed a synthetic route to the compound, forming the basis for the commercial manufacturing process. He also added the 2-chlorophenyl substitution and the 3-bromopyrazole substituent. Efforts up to this point increased the compound’s insecticidal activity 200-fold. Stevenson contributed the N-pyridinyl group and the chloro substituent para to the aniline nitrogen—which increased the insecticidal activity another fivefold—and shortly afterward prepared Rynaxypyr.

During those optimization efforts, Cordova characterized Rynaxypyr’s mode of action, determining its novel insect-specific activation of calcium ion channels called ryanodine receptors. Rynaxypyr activates these channels, leading to uncontrolled release of calcium ions and rapid feeding cessation, lethargy, paralysis, and death in pest insects.

“It was truly a remarkable team to be a part of,” Lahm says, “and I think all of us count that time as one of the most exciting of our careers.”

Stevenson, 53, obtained a B.S. in chemistry from Saint Louis University in 1979 and a Ph.D. in organic chemistry from the University of Illinois in 1983, under Nelson J. Leonard. After postdoctoral research at the University of Geneva from 1983 to 1985, Stevenson joined DuPont Crop Protection as a research chemist, rising in ranks to his current position of senior research fellow. Stevenson has just been honored with the DuPont 2010 Pedersen Medal. He has also received the DuPont Bolton-Carothers Innovative Science Award, the DuPont Sustainable Growth Excellence Award, and the R&D 100 Award from R&D Magazine, all in 2008.

Selby, 56, traces his interest in chemistry to influential teachers in both high school and university. “My undergraduate professor Robert Patsiga was instrumental in steering me toward a career in organic chemistry,” he says. Selby received a B.S. in chemistry from Indiana University of Pennsylvania in 1975 and a Ph.D. in organic chemistry from Indiana University, Bloomington, in 1979, under E. Campaigne. He joined DuPont Crop Protection in 1979 as a research chemist, rising to his current position of senior research fellow.

“Time does fly when you’re having fun,” Selby says of his 30 years at DuPont Crop Protection. Outside of work, he has a passion for fly-fishing. But the lab is never far from his mind; “Fly-fishing and discovery chemistry are very similar in some ways,” he says. “You never know if that next hole will bring success or bust. Either way, there’s always more stream to be explored.”

Selby has just been honored with the DuPont 2010 Pedersen Medal. He has also received the DuPont Bolton-Carothers Innovative Science Award, the DuPont Sustainable Growth Excellence Award, and the R&D 100 Award, all in 2008.

Freudenberger, 49, was interested in medical school when he enrolled in the chemistry program at the University of Cincinnati, where he received a B.S. in 1982. But within one semester, he realized that he “liked science too much.” After two years of undergraduate research under Milton Orchin, he decided to pursue a Ph.D. in inorganic chemistry instead, which he received from Massachusetts Institute of Technology in 1986, working under Richard R. Schrock. After postdoctoral research at the University of California, Berkeley, from 1986 to 1988, he joined DuPont Specialty Chemicals. In 1995, he transferred to Crop Protection, where he is now a research fellow. Freudenberger has also been honored with the DuPont Bolton-Carothers Innovative Science Award, the DuPont Sustainable Growth Excellence Award, and the R&D 100 Award, all in 2008.

Cordova, 46, obtained a B.A. in biology from the University of Delaware in 1985 and an M.S. in biomedical engineering from Drexel University in 1996. From 1985 to 1987, Cordova characterized chemical warfare agent inhibitors at the U.S. Army Medical Research Institute of Chemical Defense. He joined DuPont Crop Protection in 1987 as an associate scientist and is now a section research biologist, elucidating modes of action of insecticides and nematocides, as well as developing target-site assays. Cordova received the DuPont Sustainable Growth Excellence Award and the R&D 100 Award in 2008.

The award address will be presented before the Division of Agricultural Chemistry.

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