Biocatalytic Formal Anti-Markovnikov Hydroamination and Hydration of Aryl Alkenes

Abstract

Biocatalytic anti-Markovnikov alkene hydroamination and hydration were achieved based on two concepts involving enzyme cascades: epoxidation–isomerization–amination for hydroamination and epoxidation–isomerization–reduction for hydration. An Escherichia coli strain coexpressing styrene monooxygenase (SMO), styrene oxide isomerase (SOI), ω-transaminase (CvTA), and alanine dehydrogenase (AlaDH) catalyzed the hydroamination of 12 aryl alkenes to give the corresponding valuable terminal amines in high conversion (many ≥86%) and exclusive anti-Markovnikov selectivity (>99:1). Another E. coli strain coexpressing SMO, SOI, and phenylacetaldehyde reductase (PAR) catalyzed the hydration of 12 aryl alkenes to the corresponding useful terminal alcohols in high conversion (many ≥80%) and very high anti-Markovnikov selectivity (>99:1). Importantly, SOI was discovered for stereoselective isomerization of a chiral epoxide to a chiral aldehyde, providing some insights on enzymatic epoxide rearrangement. Harnessing this stereoselective rearrangement, highly enantioselective anti-Markovnikov hydroamination and hydration were demonstrated to convert α-methylstyrene to the corresponding (S)-amine and (S)-alcohol in 84–81% conversion with 97–92% ee, respectively. The biocatalytic anti-Markovnikov hydroamination and hydration of alkenes, utilizing cheap and nontoxic chemicals (O2, NH3, and glucose) and cells, provide an environmentally friendly, highly selective, and high-yielding synthesis of terminal amines and alcohols.

Accessing Enantiopure Epoxides and Sulfoxides: Related Flavin‐Dependent Monooxygenases Provide Reversed Enantioselectivity

“…[9,[11][12][13][14] There is already a huge set of substrates that are known to be converted by these enzymes in a regio-and enantioselective fashion, which illustrates their biotechnological potential (Scheme 1). [15][16][17][18]19,[20][21][22][23][24][25][26][27][28][29][30][31] Upscaling of biotransformations and liquid-two-phase systems [26,28,29,[32][33][34][35]36,[37][38][39][40] as well as enzyme cascade applications [20,41] and co-substrate regeneration experiments [18,23,26,32,42,43] were performed to fathom their applicability in an industrial process. As a consequence, they are currently considered as candidates for biotechnological processes.…”

Whole‐Cell Cascade Biotransformations for One‐Pot Multistep Organic Synthesis

“…2) Aldehydes are often reduced to alcohols with endogenous ADHs or reductases. An E. coli RARE strain with deletion of six genes of ADHs and reductases could be a useful host, and we have proved this in a recent cascade . Alternatively, expressing a heterogenous ADH (AlkJ) has been shown to counteract with the undesired aldehyde reduction .…”

“…Very recently, we designed two 3‐step cascades for formal anti ‐Markovnikov hydroamination and hydration of styrenes (Scheme a, b) . The unique regioselectivity originates from SOI‐(styrene oxide isomerase)‐catalyzed highly regioselective Meinwald rearrangement of ( S )‐styrene oxide to phenylacetaldehyde.…”

Extending Designed Linear Biocatalytic Cascades for Organic Synthesis

“…An E. coli strain co‐expressing styrene monooxygenase (SMO), styrene oxide isomerase (SOI), transaminase ( Cv TA), and alanine dehydrogenase (AlaDH) was applied for the hydroamination of styrene derivatives, leading to the corresponding terminal amines with high conversion (from 45 to >99 %) and exclusive anti‐Markovnikov selectivity (>99 : 1). Another E. coli strain co‐expressing SMO, SOI, and phenylacetaldehyde reductase (PAR) catalyzed the hydration of the same styrene derivatives to their corresponding terminal alcohols with high conversion (from 60 to >99 %) and excellent anti‐Markovnikov selectivity (>99 : 1) …”