Recent progress in directed evolution of stereoselective monoamine oxidases

Abstract

Monoamine oxidases (MAOs) use molecular dioxygen as oxidant to catalyze the oxidation of amines to imines. This type of enzyme can be employed for the synthesis of primary, secondary, and tertiary amines by an appropriate deracemization protocol. Consequently, MAOs are an attractive class of enzymes in biocatalysis. However, they also have limitations in enzyme-catalyzed processes due to the often-observed narrow substrate scope, low activity, or poor/wrong stereoselectivity. Therefore, directed evolution was introduced to eliminate these obstacles, which is the subject of this review. The main focus is on recent efforts concerning the directed evolution of four MAOs: monoamine oxidase (MAO-N), cyclohexylamine oxidase (CHAO), D-amino acid oxidase (pkDAO), and 6-hydroxy-D-nicotine oxidase (6-HDNO).

Asymmetric Synthesis of a Key Dextromethorphan Intermediate and Its Analogues Enabled by a New Cyclohexylamine Oxidase: Enzyme Discovery, Reaction Development, and Mechanistic Insight

“…However, the low substrate concentration reported (10 mM) limits their practical synthesis potential. In this context, herein we report that a new CHAO from Erythrobacteraceae bacterium CCH12-C2 discovered by genome mining, named CHAO CCH12‑C2 , was able to deracemize 100 mM 1a under Turner’s deracemization conditions − to afford ( S )- 1a in 67% isolated yield and 96% ee at a gram scale (Scheme B). The determined co-crystal structure of CHAO CCH12‑C2 complexed with the product 1-(4-methoxybenzyl)- 3,4,5,6,7,8-hexahydroisoquinoline [1-(4-methoxybenzyl)-HHIQ, 2a ] combined with the structure-guided mutagenesis study provided important mechanistic insights.…”

Recent trends in biocatalysis

“…267 Another approach for accessing chiral THIQs is via enantioselective oxidation with MAO. 268,269 Although the natural substrates for MAO are usually small primary amines, the Turner group had pioneered in engineering MAO-N from Aspergillus niger (A. niger) for bulky secondary and tertiary bulky amines, such as 1-phenyltetrahydroisoquinoline (1-phenyl-THIQ, Scheme 2F). 270 By enantioselective oxidation with MAO-N D11 and simultaneous reduction with BH 3 -NH 3 , racemic 1-phenyl-THIQ was deracemised to (S)-1-phenyl-THIQ (a precursor for Solifenacin) in excellent optical purity and yield.…”

Engineered Monoamine Oxidase-Catalyzed Deracemization of Sterically Hindered Acylaminomethyl-tetrahydroisoquinoline: Asymmetric Synthesis of (R)-(−)-Praziquantel and Its Analogues

“…Flavin-dependent monoamine oxidases (MAOs) are a class of enzymes naturally performing molecular oxygen-mediated oxidation of amines to produce imines . Over the past two decades, several MAOs identified from fungi and bacteria have been substantially engineered to result in enzyme variants displaying a remarkably extended substrate scope. − In particular, the Turner group has developed and applied a series of evolved MAO variants derived from MAO-N, a monoamine oxidase originating from Aspergillus niger, to the stereoselective synthesis of a wide range of chiral amines through a one-pot deracemization process, comprising a MAO-catalyzed enantioselective oxidation and a nonselective chemical reduction. ,,,− Notably, to the best of our knowledge, the application of monoamine oxidase to the synthesis of ( R )-PZQ or its synthetic intermediates has not yet been reported. Prompted by the success of MAO-catalyzed synthesis of chiral 1-alkyl-, 1-benzyl-, and 1-phenyl-tetrahydroisoquinolines (THIQs), ,,,,− we envisioned that stereoselective synthesis of ( R )-1-cyclohexanecarboxylaminomethyl-THIQ (( R )- 1a , Scheme B), a demonstrated key intermediate en route to ( R )-PZQ, , through MAO-catalyzed deracemization (Scheme B), could be a viable way leading to the stereoselective, chemoenzymatic synthesis of ( R )-PZQ.…”