One synthetic strategy to manufacture the world's best-selling drug Lipitor relies on an enzyme that was evolved in a lab to produce an enantiomerically pure chiral building block. The "evolved" nitrilase enzyme is but one example of how Manfred T. Reetz's pioneering development of directed evolution to do asymmetric synthesis has yielded benefits to scientists and patients worldwide. It also has earned Reetz—currently a director at the Max Planck Institute for Coal Research, in Mülheim, Germany—the 2009 Arthur C. Cope Award, for his "development of a new approach to catalysis, namely the directed evolution of enantioselective and thermostable enzyme."
"Reetz has made a number of truly outstanding contributions to chemical science in many areas, particularly organic synthesis, organometallic chemistry, and homogeneous catalysis," notes Nobel Laureate Ryoji Noyori, who is also the president of Wako, Japan-based RIKEN. "However, his most impressive achievement since the 1990s has been a novel approach to asymmetric catalysis, namely the directed evolution of enantioselective enzymes for use as biocatalysts in synthetic organic chemistry. This is truly fundamental and conceptually innovative."
"I'm thrilled to receive the Cope Award," Reetz says. "It is really a great honor to be among the list of recipients."
Born in 1943 in Hirschberg, Germany, Reetz spent part of his youth in Germany before moving with his family to St. Louis, Mo., at the age of nine. After completing high school in the U.S., Reetz began studying chemistry at Washington University in St. Louis in 1965. "I wanted since my teenage days to become a chemist, perhaps because my father was an industrial chemist at Monsanto," Reetz says. He also worked at the company as a part-time student technician in the 1960s, only a few doors away from William S. Knowles, who later received the Nobel Prize—together with Noyori and Barry Sharpless of Scripps Research Institute—in 2001 for asymmetric transition-metal catalysis.
Soon after receiving a master's degree from the University of Michigan, Ann Arbor, Reetz headed back to Germany to complete a Ph.D. in organic chemistry in 1969 at the University of Göttingen, in Germany, under the guidance of the late Ulrich Schöllkopf. This was followed by a postdoctoral stay with Reinhard W. Hoffmann at the University of Marburg, in Germany.
After professorship positions at the University of Marburg and the University of Bonn, Reetz was recruited in 1991 to serve as director of the Max Planck Institute for Coal Research, where Karl Ziegler famously developed the catalysts for polymerizing ethylene in the 1950s, ushering in the era of plastics.
Reetz says moving to the Max Planck Institute was integral to both the feasibility and success of this award-winning enzyme evolution. Germany's Max Planck Institutes are called a paradise by some scientists because directors are provided generous operating budgets, excellent facilities, and relatively few grant-writing responsibilities. "We can focus on risky projects," without the pressure of having to constantly publish and write grants, Reetz explains.
The directed-evolution work was one such risky project because it married two very different fields—molecular biology and organic synthesis. The technique also required the development of costly high-throughput-screening analytical apparatus. "Robotic equipment was expensive to buy in the 1990s, and that would have been difficult to do at a university," notes Reetz.
The project had its inception in 1994, when Reetz read about DNA shuffling, a technique for creating new DNA sequences quickly, by Willem P. C. Stemmer of the Affymax Research Institute (Nature 1994, 370, 389). "It inspired me to read more about the emerging field of directed evolution, and I began to speculate that it might be possible to apply Darwinian principles in the laboratory to evolve enantioselective enzymes for use in synthetic organic chemistry," Reetz recalls. "This required a completely different way of thinking than in the traditional field of asymmetric catalysis based on transition metals."
It took several years of work before the first proof of principle was published in 1997 in Angewantde Chemie International Edition. The paper reported a one-order-of-magnitude improvement compared with the wild-type enzyme in the selectivity factor for making a chiral carboxylic acid ester using an evolved lipase enzyme.
"One of the prime challenges in that early study was the necessity to develop a high-throughput-screening system for evaluating thousands of potentially enantioselective mutants, because such analytical techniques were unknown at the time," Reetz notes. To do so, Reetz's team built high-throughput enantiomeric-excess screens based on mass spectrometry, circular dichroism, and even infrared cameras measuring heat evolution.
Reetz and his colleagues then went on to direct the evolution of mono-oxygenases, so that they produce chiral ketones and lactones with enantiomeric excesses unrivaled by synthetic catalysts.
"This pioneering work by Reetz had an enormous technological impact. Many other academic and industrial groups worldwide were inspired to apply these strategies in the directed evolution of other enantioselective enzymes," Noyori says.
These days, Reetz is concentrating on developing methodology to make directed evolution faster and more efficient. In particular he has developed Iterative Saturation Mutagenesis to quickly produce high-quality DNA mutation libraries that are the essential gear for directed-evolution laboratories. The technique is also economical because it "drastically reduces the size of the libraries and thus the necessary molecular biological work, as well as the screening effort, while providing much better mutants," Noyori notes.
Reetz also recently has been making inroads into applying directed evolution to the production of "hybrid catalysts," which are enzymes with anchored synthetic transition metals or ligands. His lab recently evolved enzymes that can perform Rh-catalyzed asymmetric olefin hydrogenation.
"The depth and breadth of Reetz's knowledge, together with his creative instincts, have enabled him to make key contributions across nearly the entire range of our field," Sharpless says. These include, "for example, new synthetic methods, asymmetric reagents and catalysts, creation of an ingenious method for rapid screening of homo- or heterogeneous catalysts via heat evolution with an infrared camera, and mechanistic insights into crucial reactivity issues involving both experiment and theory."
To get the inspiration for the experiments reported in his more than 450 publications, Reetz likes to either sit alone in a silent room or "go to the lab to kick around ideas with my creative coworkers," an activity he finds very rewarding, he says.
Reetz is a father to four children and enjoys listening to classical music with his wife. He is also a big fan of tennis, a game he used to play avidly. In fact, while working as a court attendant at Washington University in St. Louis in his early college days, Reetz recalls, he regularly beat eight-time Grand Slam champion Jimmy Connors. "Of course, I was 19 that year and he was 11," Reetz adds with a laugh. "The next summer I didn't have a chance against him."