Editorial Cite This: Chem. Rev. 2018, 118, 1−3
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Introduction: Biocatalysis in Industry
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well as engineered variants which provide the so called antiPrelog or R enantiomers of these important chiral synthons. Beginning in the late 1970s with pioneering work of Michael Smith and later amplified by contributions from Pim Stemmer and Frances Arnold, microbiologists began developing techniques that enabled directed evolution of enzymes.7 This approach has been used to produce engineered or customized enzymes that are tailored to unnatural substrates and reaction conditions far removed from those found in natural systems. In a seminal 1993 paper by Frances Arnold, for example, it was demonstrated that subtilisin E could be engineered through successive rounds of random mutagenesis to be increasingly tolerant of dimethylformamide (DMF) as an organic cosolvent, with one variant being 256 times more active in 65% DMF versus wild-type.8 In addition to addressing cosolvent stability deficiencies commonly seen with wild-type enzymes, an array of genetic engineering techniques have been employed to address acceptance of unnatural substrates, to deliver complimentary stereoselectivity,9 to address substrate, product, or co-factor inhibition issues, and to improve thermal stability or pH stability.10 The widespread adoption of modern protein engineering has led to a number of remarkable applications. Substrates which are dramatically distinct from natural ligands are now able to be transformed with efficiencies suitable for industrial applications. An early example of this was the development of a ketoreductase (CDX-026) capable of reducing the large, hydrophobic ketone substrate 1 to yield alcohol 2, which serves as a precursor to montelukast, widely used to treat asthma and seasonal rhinitis (Scheme 1).11 A Baeyer Villeger Monooxygenase has also been engineered to enantioselectively oxidize sulfide 3 to provide esomeprazole 4, used to treat acid reflux (Scheme 2).12 Transaminases have also become widely recognized as a platform for preparing chiral amines from prochiral ketones. One particularly noteworthy application is in the production of sitagliptin 6, a DPP4 inhibitor used for the treatment of type II diabetes. While no detectable activity could initially be established for the sitagliptin ketone 5, initial rounds of evolution using a truncated analogue enabled measurable conversion of the ketone of interest, ultimately leading to the development of a biocatalyst with activity suitable for commercial manufacturing (Scheme 3). Another interesting example is the engineering of carbonic anhydrase. While the substrate in this instance (CO2) is its native ligand and is very simple, the work is noteworthy for the severity of the conditions which the enzyme was engineered to sustain (107 °C, pH > 10).13 More recently, protein systems have even been engineered to deliver chemical reactions such as enantioselective cyclopropanations,14 silylations,15 and borylation16 reactions which are unprecedented in nature.
or the purposes of this thematic issue of Chemical Reviews, we define biocatalysis as the use of enzymes in their purified form, as part of a cell lysate, or whole cells, to convert a molecular substrate, particularly a substrate not known to be transformed by that enzyme in natural systems, into a product. Louis Pasteur provided the first example of modern biocatalysis in 1858 by demonstrating the resolution of racemic tartaric acid through fermentation with a variety of microorganisms, including the common mold Penicillium glaucum.1 In these experiments, (+)-tartaric acid was consumed much faster than (−)-tartaric acid, allowing for isolation of the latter. Towards the end of the 19th century, Emil Fischer proposed the “lock and key” model for enzyme catalysis,2 and Buchner demonstrated that cell-free extracts were capable of catalyzing fermentation processes.3 These seminal developments would lead to a rapidly expanding number of applications of biocatalysis in the 20th century, including many important industrial examples. This growth has been driven by an array of factors. Enzymes can be thought of as renewable catalysts. Unlike metal based alternatives that rely on mining and harsh, energy intensive processing, biocatalysts are biodegradable and easily replaced through inexpensive and environmentally benign fermentation processes. The minimal environmental and economic burden posed by enzymes is further diminished by the potential to engineer even more active variants than can be found in nature, to optimize expression efficiencies and fermentation yields, and to immobilize and reuse these powerful catalysts. The following are just a few of the many examples of how enzymes are improving industrial chemical processing. Nitrile hydratases have now supplanted an earlier Cu based method for converting acrylonitrile to acrylamide, the monomer used to prepare polyacrylamide.4 This process is now conducted on tens of thousands of metric tons per year. Likewise, conventional bleaching processes in the textile industry, which previously used Cl2 or NaOCl, can now be carried out with the more benign H2O2.5 This switch was initially hampered by the fact that residual peroxide was detrimental to subsequent dying processes. This issue is obviated by the use of peroxidases which quantitatively convert residual H2O2 to molecular oxygen and water, allowing for more economical and environmentally friendly processing. Another nitrile hydratase application involves the regioselective partial hydrolysis of adiponitrile to form 5-cyanovaleramide, which serves as a starting material for the Dupont herbicide azafenidin (Milestone).5 Some of the most powerful examples of biocatalytic applications exploit the chiral nature of these catalysts. In fact, the R and S nomenclature commonly used to define the orientation of substituents of a chiral center as popularized by Prelog and others was first described in the context of the products formed by the reduction of prochiral ketones by alcohol dehydrogenases (ADHs).6 While the majority of natural organisms express ADHs providing the S enantiomer, a number ADHs are now available both from natural sources as © 2018 American Chemical Society
Special Issue: Biocatalysis in Industry Published: January 10, 2018 1
DOI: 10.1021/acs.chemrev.7b00741 Chem. Rev. 2018, 118, 1−3
Chemical Reviews
Editorial
Scheme 1. Biocatalyic Approach to Montelukast
Scheme 2. BVMO Catalyzed Sulfide Oxidation to Produce Esomeprazole
Scheme 3. Preparation of Sitagliptin Using an Engineered Transaminase
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The reviews in this thematic issue cover a number of emerging developments in the field including expanding classes of reactions (transaminases, imine reductases, enereductases, halogenases, ammonia lyases, and amino mutases). There are also reviews covering strategies in biocatalysis including the development of artificial metalloenzymes, non-natural reactions catalyzed by enzymes, biocatalytic cascades, enzyme catalyzed protein conjugations, metabolic pathways for chemical biosynthesis, and computations and library design strategies for enzyme engineering. Together, these reviews offer a glimpse of the types of biocatalysts that are currently used in industry and others that, with further development, might be suitable for practical applications in the near future.
Jared C. Lewis: 0000-0003-2800-8330 Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS. Biographies
Greg Hughes,* Principle Scientist Department of Process Research and DevelopmentMerck Sharp & Dohme Corporation, Rahway, New Jersey 07065, United States
Jared C. Lewis,* Assistant Professor Searle Chemistry Lab, Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
AUTHOR INFORMATION
Photo by Carolyn Ann Ryan Photography
Corresponding Authors
Gregory J. Hughes completed his B.Sc. at the University of New Brunswick in 1994. After a brief internship at Merck Frosst in Kirkland, Québec, Greg began doctoral studies at the University of
*G.H.: E-mail,
[email protected]. *J.C.L.: E-mail,
[email protected]. 2
DOI: 10.1021/acs.chemrev.7b00741 Chem. Rev. 2018, 118, 1−3
Chemical Reviews
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Toronto in 1996 with Prof. Mark Lautens. Upon completion of his Ph.D., he began an NSERC postdoctoral fellowship at MIT in the labs of Prof. Buchwald before joining the Merck Process Research and Development Department in 2002, where he is currently a Principle Scientist.
Jared C. Lewis received his B.Sc. in chemistry in 2002 from the University of Illinois, working with Eric Oldfield, and his Ph.D. in 2007 from the University of California, Berkeley, under the direction of Jonathan Ellman and Robert Bergman. He carried out postdoctoral research in Frances Arnold’s laboratory at the California Institute of Technology. He began his independent career in 2011 at the University of Chicago, where he is an Assistant Professor. His research involves engineering and evolving natural and artificial enzymes for selective catalysis.
REFERENCES (1) Pasteur, L. C.R. Seances Acad. Sci 1958, 46, 615. (2) Fischer, E. Ber. Dtsch. Chem. Ges. 1894, 27, 2985. (3) Buchner, E. Ber. Dtsch. Chem. Ges. 1897, 36, 117. (4) Hann, E. C.; Eisenberg, A.; Fager, S. K.; Perkins, N. E.; Gallagher, F. G.; Cooper, S. M.; Gavagan, J. E.; Stieglitz, B.; Hennessey, S. M.; DiCosimo, R. Biorg. Med. Chem. 1999, 7, 2239. (5) Biocatalysis; Bommarius, A. S., Riebel, B. R., Eds.; Wiley-VCH: Weinheim, Germany, 2004. (6) Prelog, V. Pure Appl. Chem. 1964, 9, 119. (7) Recent reviews of directed evolutions: (a) Packer, M. S.; Liu, D. R. Nature Rev. Genet. 2015, 16, 379. (b) Reetz, M. T. Angew. Chem., Int. Ed. 2011, 50, 138. (c) Romero, P. A.; Arnold, F. H. Nature Rev. Mol. Cell. Biol. 2010, 10, 866. (8) Chen, K.; Arnold, F. H. Proc. Natl. Acad. Sci. U. S. A. 1993, 90, 5618. (9) (a) May, O.; Nguyen, P. T.; Arnold, F. H. Nat. Biotechnol. 2000, 18, 317. (b) Tang, W. L.; Li, Z.; Zhao, H. Chem. Commun. 2010, 46, 5461. (10) Reetz, M. T.; Carballeira, J. D.; Vogel, A. Angew. Chem., Int. Ed. 2006, 46, 7745. (11) Liang, J.; Lalonde, J.; Borup, B.; Mitchell, V.; Mundorff, E.; Trinh, N.; Kochrekar, D. A.; Ramachandran, N. C.; Pai, G G. Org. Process Res. Dev. 2010, 14, 193. (12) Wilson, R. Chim. Oggi-Chem. Today 2015, 33, 50. (13) Alvizo, O.; Nguyen, L. J.; Savile, C. K.; Bresson, J. A.; Lakhapatri, S. L.; Solis, E. O. P.; Fox, R. J.; Broering, J. M.; Benoit, M. R.; Zimmerman, S. A.; Novick, S. J.; Liang, J.; Lalonde, J. J. Proc. Natl. Acad. Sci. U. S. A. 2014, 111, 16436. (14) Coelho, P. S.; Brustad, E. M.; Kannan, A.; Arnold, F. H. Science 2013, 339, 307. (15) Kan, S. B.; Lewis, R. D.; Chen, K.; Arnold, F. H. Science 2016, 354, 1048. (16) Kan, S. B.; Huang, X.; Gumulya, Y.; Chen, K.; Arnold, F. H. Nature 2017, 552, 132.
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DOI: 10.1021/acs.chemrev.7b00741 Chem. Rev. 2018, 118, 1−3
