YEAR IN CHEMISTRY RESEARCH BIOCATALYSIS
ENZYMES SPARKED INNOVATIVE CHEMISTRY Advances this year included improved oxidations, decarboxylations, and alkylations
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nzymes play a key role in chemistry research and in the chemical and food processing industries. Evidence comes from the pages of C&EN: A search shows that enzymes were covered in about 200 articles this year, roughly four articles per issue. Among those were many tales of cutting-edge discoveries. For example, researchers hunted down new enzymes capable of catalyzing syntheses useful to the biotech industry, and they artificially evolved known enzymes to orchestrate tough organic reactions. “I believe we are entering a new era of enzyme discovery,” says Emily P. Balskus of Harvard University. “Expanding the types of molecules we can access using biocatalysis and synthetic biology requires that we identify enzymes that perform new chemical transformations, either through discovery or engineering.” Here are three of C&EN’s favorite enzyme feats of 2017.—STU BORMAN
Friedel-Crafty bacteria Balskus’s group at Harvard pinpointed the enzymes that cyanobacteria use to synthesize aromatic natural products called cylindrocyclophanes. In 1877, Charles Friedel and James Crafts discovered that a Lewis acid could add an alkyl halide’s alkyl group to an aromatic ring. Balskus and coworkers showed that cyanobacteria developed the same type of reaction first (Nat. Chem. Biol. 2017, DOI: 10.1038/nchembio.2421). One enzyme they found, CylK, decorates aromatic rings with alkyl groups from alkyl halides. Another, CylC, generates the alkyl chlorides that the cyanobacteria need to run the CylK reaction (shown in scheme). The researchers are currently trying to solve CylK’s crystal structure and hope to engineer the enzyme to accept a wider variety of building blocks as substrates. CylC halogenase
O ACP
Cl –
S
O ACP
S Cl
ACP = Acyl carrier protein
HO HO
OH
OH
CylK alkylating enzyme
2x HO
Cylindrocyclophane F
Cl OH
Evolved oxidizer To oxidize the end carbon of a terminal alkene to form an aldehyde—an anti-Markovnikov alkene oxidation— chemists typically have had to use nonenantioselective and fairly unproductive methods. Frances H. Arnold of Caltech and coworkers employed a technique called directed evolution to develop an anti-Markovnikov enzyme that works better. Directed evolution is an iterative protein-mutation and screening process that endows enzymes with abilities they weren’t born with. Arnold’s team identified 12 amino acid substitutions (red circles) that convert a conventional alkene oxidation enzyme called P450LA1 into a predominantly stereoselective anti-Markovnikov catalyst called aMOx (Science 2017, DOI: 10.1126/science.aao1482). The productivity of aMOx (heme group is black, blue, and red stick structure) is nearly 400 times that of some existing commercial alkene oxidation catalysts.
A team led by Fred Beisson of the French Alternative Energies & Atomic Energy Commission found that microalgae possess an unusual enzyme that harnesses light to decarboxylate fatty acids to alkanes or alkenes (Science 2017, DOI: 10.1126/science.aan6349). The researchers investigated microalgae that synthesize hydrocarbons but don’t have genes for the enzymes that typically perform that task. By purifying enzymes from the microalgae, they identified fatty acid photodecarboxylase (shown with the cofactor flavin adenine dinucleotide and a palmitic acid substrate as stick structures), a photoenzyme with unprecedented activity: converting fatty acids into 14- to 18-carbon alkanes or alkenes. The new photoenzyme could be useful for producing biobased hydrocarbons.
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C&EN | CEN.ACS.ORG | DECEMBER 11/18, 2017
C R E D I T: S CI E NC E ( BOTH )
Enlightening discovery
PROCESS CHEMISTRY
Flow chemistry advanced in industry Lilly chemists capitalized on continuous chemical manufacturing to make a chemotherapy drug candidate
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by regulatory agencies for drug produclow chemistry has been steadily tion (Science 2017, DOI: 10.1126/science. gaining ground in academia in reaan0745). cent years, and in 2017 the continuKevin P. Cole, the report’s lead ous chemical synthesis method—in N author, explained in June that which tubes HN CN the group decided to go for H3C and T-junction mixers N O replace the flasks and O a flow approach because N Lilly needed only 24 kg stir bars used for batch reN H O– of the drug candidate. actions—managed to make H2O O OH Making prexasertib inroads in the pharmaceuin batch equipment tical industry. One mileNH3+ stone: Chemists at Eli Prexasertib monolactate monohydrate would have required an extensive cleanup Lilly & Co. used continafterward because the compound is pouous-flow chemistry as a safer, faster, and A walk-in fume hood contains newly tent and cytotoxic, so any residue could cheaper way to make the chemotherapy designed continuous-flow equipment at Eli potentially contaminate future reactions. drug candidate prexasertib monolactate Lilly’s facility in Kinsale, Ireland. The small flow setup the team used could monohydrate. Flow chemistry was popular elsebe dedicated to making this single comThe Lilly team set up eight continuous where this year. Flow chemistry company process steps to make the compound. One pound and then discarded, if necessary, Snapdragon partnered step used hydrazine, a O with Pfizer to prepare component of rocket H O N O Li H H the highly reactive fuel, which would have H n-Hexyllithium O reagent allenyllithium been too dangerous to O N Chiral zinc complex H en route to making an use in a batch process. H H OH important drug interBut perhaps the most Allene Allenyllithium Chiral homopropargyl 𝛍-amino alcohol mediate. Snapdragon notable part of this synat no great cost, Cole said. The success of also formed a pact with Johnson Matthey, thesis is that the Lilly chemists linked the a leading supplier of bulk pharmaceutical using flow to make prexasertib prompted final stages in the continuous manufacchemicals, to collaborate on flow chemLilly to build a continuous-flow facilituring process to quality-control systems istry for drug manufacturing.—BETHANY ty in Kinsale, Ireland, which opened in to achieve current Good Manufacturing October. Practices (cGMPs) standards required HALFORD
CR E DI T: E L I L I L LY & CO.
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DECEMBER 11/18, 2017 | CEN.ACS.ORG | C&EN
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