Engineered Imine Reductase for Asymmetric Synthesis of Dextromethorphan Key Intermediate

Area of Science:

• Biocatalysis
• Enzyme Engineering
• Organic Synthesis

Background:

• The synthesis of dextromethorphan, a nonopioid antitussive, relies on the key intermediate (S)-1-(4-methoxybenzyl)-1,2,3,4,5,6,7,8-octahydroisoquinoline ((S)-1-(4-methoxybenzyl)-OHIQ).
• Efficient and enantioselective synthesis of this intermediate is critical for industrial production.

Purpose of the Study:

• To engineer an enzyme with significantly improved catalytic efficiency for the synthesis of (S)-1-(4-methoxybenzyl)-OHIQ.
• To evaluate the potential of the engineered enzyme for industrial-scale production of the dextromethorphan intermediate.

Main Methods:

• Directed evolution and enzyme engineering were employed to enhance the catalytic activity of the wild-type IR61 enzyme.
• The engineered enzyme variant, designated M4 ((S)-IR61-V69Y/P123A/W179G/F182I/L212V), was characterized for its performance.

Main Results:

• Enzyme variant M4 exhibited a 766-fold improvement in catalytic efficiency compared to the wild-type IR61.
• M4 completely converted 200 mM of the precursor substrate into (S)-1-(4-methoxybenzyl)-OHIQ with a 77% isolated yield.
• The reaction achieved >99% enantiomeric excess and a high space-time yield of 542 g L⁻¹ day⁻¹.

Conclusions:

• The engineered enzyme M4 demonstrates exceptional catalytic efficiency and selectivity for the synthesis of (S)-1-(4-methoxybenzyl)-OHIQ.
• The high performance metrics of M4 indicate its significant potential for the industrial-scale synthesis of the dextromethorphan intermediate.