Cascading Old Yellow Enzyme, Alcohol Dehydrogenase and Glucose Dehydrogenase for Selective Reduction of (E/Z)-Citral to (S)-Citronellol

Yunpeng Jia,Qizhou Wang,Yingting Feng,Xueting Zhou,Xiangxian Ying,Lijun Jin,Duxia Yang,Chenze Lu,Binbin Feng,Jingjing Qiao

doi:10.3390/catal11080931

Yunpeng Jia, Qizhou Wang + Show 8 more

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https://doi.org/10.3390/catal11080931

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Abstract

Citronellol is a kind of unsaturated alcohol with rose-like smell and its (S)-enantiomer serves as an important intermediate for organic synthesis of (-)-cis-rose oxide. Chemical methods are commonly used for the synthesis of citronellol and its (S)-enantiomer, which suffers from severe reaction conditions and poor selectivity. Here, the first one-pot double reduction of (E/Z)-citral to (S)-citronellol was achieved in a multi-enzymatic cascade system: N-ethylmaleimide reductase from Providencia stuartii (NemR-PS) was selected to catalyze the selective reduction of (E/Z)-citral to (S)-citronellal, alcohol dehydrogenase from Yokenella sp. WZY002 (YsADH) performed the further reduction of (S)-citronellal to (S)-citronellol, meanwhile a variant of glucose dehydrogenase from Bacillus megaterium (BmGDHM6), together with glucose, drove efficient NADPH regeneration. The Escherichia coli strain co-expressing NemR-PS, YsADH, and BmGDHM6 was successfully constructed and used as the whole-cell catalyst. Various factors were investigated for achieving high conversion and reducing the accumulation of the intermediate (S)-citronellal and by-products. 0.4 mM NADP+ was essential for maintaining high catalytic activity, while the feeding of the cells expressing BmGDHM6 effectively eliminated the intermediate and by-products and shortened the reaction time. Under optimized conditions, the bio-transformation of 400 mM citral caused nearly complete conversion (>99.5%) to enantio-pure (S)-citronellol within 36 h, demonstrating promise for industrial application.

Highlights

Citronellol is one of essential components in various kinds of perfumes and a promising molecule with pharmacological activities [1,2]
Old yellow enzymes are known to reduce the conjugated C=C bond of α,β-unsaturated aldehydes and ketones [13,14], alcohol dehydrogenases catalyze the reversible reduction of the C=O bond [15,16,17]
The reduction of (E/Z)-citral to (S)-citronellal is the key step in the cascade reaction, which requires old yellow enzyme with high activity and strict (S)-enantioselectivity

Summary

Introduction

Citronellol is one of essential components in various kinds of perfumes and a promising molecule with pharmacological activities [1,2]. The synthesis of citronellol commonly relies on chemical methods starting from citral, geraniol, or citronellal [7,8,9], but rarely on biotransformation [10,11]. Old yellow enzymes are known to reduce the conjugated C=C bond of α,β-unsaturated aldehydes and ketones [13,14], alcohol dehydrogenases catalyze the reversible reduction of the C=O bond [15,16,17]. The FMN-containing old yellow enzymes catalyze the asymmetric hydrogenation of citral at the expense of a nicotinamide cofactor, producing citronellal with one stereocenter. Old yellow enzymes require the substrate bearing electron-withdrawing group and do not function on geraniol

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