2006 Greener Reaction Conditions Award
Directed Evolution of Three Biocatalysts to Produce the Key Chiral
for Atorvastatin, the Active Ingredient in Lipitor®
Innovation and Benefits: Codexis developed cutting-edge genetic methods to create “designer enzymes”. Codexis applied its methods to produce enzymes that greatly improve the manufacture of the key building block for Lipitor®, one of the world's best-selling drugs. The new enzymatic process reduces waste, uses less solvent, and requires less processing equipment – marked improvements over processes used in the past. The process also increases yield and improves worker safety.
Atorvastatin calcium is the active ingredient of Lipitor®, a drug that lowers cholesterol by blocking its synthesis in the liver. Lipitor® is the first drug in the world with annual sales exceeding $10 billion. The key chiral building block in the synthesis of atorvastatin is ethyl (R)-4-cyano-3-hydroxybutyrate, known as hydroxynitrile (HN). Annual demand for HN is estimated to be about 440,000 pounds. Traditional commercial processes for HN require a resolution step with 50 percent maximum yield or syntheses from chiral pool precursors; they also require hydrogen bromide to generate a bromohydrin for cyanation. All previous commercial HN processes ultimately substitute cyanide for halide under heated alkaline conditions, forming extensive byproducts. They require a difficult high-vacuum fractional distillation to purify the final product, which decreases the yield even further.
Codexis designed a green HN process around the exquisite selectivity of enzymes and their ability to catalyze reactions under mild, neutral conditions to yield high-quality products. Codexis developed three specific enzymes using state-of-the-art, recombinant-based, directed evolution technologies to provide the activity, selectivity, and stability required for a practical and economic process. The bioengineered enzymes are so active and stable that Codexis can recover high-quality product by extracting the reaction mixture. In the first step, two of the enzymes catalyze the enantioselective reduction of a prochiral chloroketone (ethyl 4-chloroacetoacetate) by glucose to form an enantiopure chlorohydrin. In the second step, a third enzyme catalyzes the novel biocatalytic cyanation of the chlorohydrin to the cyanohydrin under neutral conditions (aqueous, pH ~7, 77–104 °F, atmospheric pressure). On a biocatalyst basis, the three enzymes have improved the volumetric productivity of the reduction reaction by approximately 100-fold and that of the cyanation reaction by approximately 4,000-fold.
The process involves fewer unit operations than earlier processes, most notably obviating the fractional distillation of the product. The process provides environmental and human health benefits by increasing yield, reducing the formation of byproducts, reducing the generation of waste, avoiding hydrogen gas, reducing the need for solvents, reducing the use of purification equipment, and increasing worker safety. The Codexis process is operated by Lonza to manufacture HN for Pfizer’s production of atorvastatin calcium.
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