Download MendeleyAsymmetric Synthesis of a Key Dextromethorphan Intermediate and Its Analogues Enabled by a New Cyclohexylamine Oxidase: Enzyme Discovery, Reaction Development, and Mechanistic Insight.
Wu, X., Huang, Z., Wang, Z., Li, Z., Wang, J., Lin, J., Chen, F.(2020) J Org Chem 85: 5598-5614
- PubMed: 32203655
- DOI: https://doi.org/10.1021/acs.joc.0c00469
- Primary Citation of Related Structures:
6LQC, 6LQL - PubMed Abstract:
( S )-1-(4-Methoxybenzyl)-1,2,3,4,5,6,7,8-octahydroisoquinoline [( S )-1-(4-methoxybenzyl)-OHIQ, ( S )- 1a ] is a key synthetic intermediate in the industrial production of dextromethorphan, one of the most widely used over-the-counter antitussives. We report here that a new cyclohexylamine oxidase discovered by genome mining, named CHAO CCH12-C2 , was able to completely deracemize 100 mM 1a under Turner's deracemization conditions to afford ( S )- 1a in 80% isolated yield and 99% ee at a semipreparative scale (0.4 mmol). When this biocatalytic reaction was scaled up to a gram scale (5.8 mmol), without reaction optimization ( S )- 1a was still isolated in 67% yield and 96% ee. The relatively higher k cat determined for CHAO CCH12-C2 was rationalized as one major factor rendering this enzyme capable of oxidizing 1a effectively at elevated substrate concentrations. Protein sequence alignment, analysis of our 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 ], and the structure-guided mutagenesis study together indicated L295 is one of the critical residues for this efficient enzymatic oxidation process and supported the presence of two cavities as well as a catalytically important "aromatic cage" formed by F342, Y433, and FAD. The synthetic applicability of CHAO CCH12-C2 was further underscored by the stereoselective synthesis of various enantioenriched 1-benzyl-OHIQ derivatives of potential pharmaceutical importance at a semipreparative scale.
Organizational Affiliation:
College of Chemical Engineering, Fuzhou University, Fuzhou 350116, P. R. China.
