Chiral Alcohols from Alkenes and Water: Directed Evolution of a Styrene Hydratase

Abstract

Enantioselective synthesis of chiral alcohols through asymmetric addition of water across an unactivated alkene is a highly sought-after transformation and a big challenge in catalysis. Herein we report the identification and directed evolution of a fatty acid hydratase from Marinitoga hydrogenitolerans for the highly enantioselective hydration of styrenes to yield chiral 1-arylethanols. While directed evolution for styrene hydration was performed in the presence of heptanoic acid to mimic fatty acid binding, the engineered enzyme displayed remarkable asymmetric styrene hydration activity in the absence of the small molecule activator. The evolved styrene hydratase provided access to chiral alcohols from simple alkenes and water with high enantioselectivity (> 99 : 1 e.r.) and could be applied on a preparative scale.

Efficient Transferase Engineering for SAM Analog Synthesis from Iodoalkanes

“…Please note that such huge increases in activity in one round of directed evolution are rare. Established approaches such as iterative site‐saturation mutagenesis [28] typically increase activity by a factor of 2–4 per round of evolution [29–35] . Although increase in activity depends on the starting activity, the improvements reported here highlight the strengths of the applied enzyme engineering strategy.…”

“…Established approaches such as iterative site-saturation mutagenesis [28] typically increase activity by a factor of 2-4 per round of evolution. [29][30][31][32][33][34][35] Although increase in activity depends on the starting activity, the improvements reported here highlight the strengths of the applied enzyme engineering strategy. We determined catalytic efficiencies (k cat /K M ) of the generated biocatalysts to compare them with SAH methylation of wild-type enzymes (k cat /K M = 580-4200 M À 1 s À 1 ) [11,22] as well as with the most efficient engineered anion MTs for SAH ethyl-ation (k cat /K M = 3.6 and 51 M À 1 s À 1 ) [22,24] generated by iterative rounds of site saturation mutagenesis.…”

A New Age of Biocatalysis Enabled by Generic Activation Modes

“…Recently, fatty acid hydratases (FAHs) attracted attention, as they use Brønsted acid catalysis to activate aliphatic olefins for hydration of unsaturated fatty acids. , While the exact Brønsted acidic site is under debate, these enzymes have recently been engineered for asymmetric hydration of aliphatic and aryl alkenes. , What stands out is that these engineered enzymes enable highly enantioselective synthesis of chiral alcohols (>99% e.e.) from simple alkenes and water in an atom economic process (Figure g).…”

“…This includes the stereoselective Prins/carbonyl-ene reaction (c), 23 interrupted, stereoselective cyclization of polyenes (d), 36,37 selective carbocation rearrangement reactions (e), 38 desymmetrization of oxetanes (f), 42 and enantioselective water addition to olefins (g). 46 Please note that many of these transformations do not have other catalytic solutions. the selective monocyclization of various polyenes with high yield, enantioselectivity (>99% e.e.)…”

Hot off the Press

“…Directed evolution of a fatty acid hydratase (FAH) from Marinitoga hydrogenitolerans has produced a biocatalyst that can perform highly enantioselective hydration of styrenes. 29 For optimal performance of the FAH biocatalysts, heptanoic acid was used to mimic fatty acid binding, resulting in the efficient, preparative scale synthesis of chiral alcohols (Scheme 2). The total synthesis of (+)-xyloketal B ( 28 ), a pentacyclic fungal marine natural product, has been reported using an enzymatic benzylic hydroxylation as the key step.…”