(R)-Citronellal is a key chiral precursor of high-value chemicals, such as the best-selling flavor compound (−)-menthol; however, the conventional synthesis suffers from low yield and unsatisfactory enantioselectivity. In this study, we developed a highly atom-efficient hydrogen-borrowing cascade for the synthesis of (R)-citronellal from geraniol using alcohol dehydrogenase from Escherichia coli K12 (AdhP) and ene-reductase from Saccharomyces cerevisiae YJM1341 (OYE2p). The key rate-limiting enzyme, AdhP, was subjected to structure-guided semirational engineering, and the triple mutant AdhP^{260T/284A/268P} (M3) was obtained that demonstrated a 1.28-fold improvement in catalytic efficiency (k_cat/K_m) toward geraniol. After optimization of the reaction conditions, the hydrogen-borrowing cascade system achieved the conversion of 23.14 g/L geraniol into (R)-citronellal at a conversion rate of 98.23% with 96.7% ee. This work represents an alternative approach for the biosynthesis of (R)-citronellal without sacrificing a cosubstrate or additional enzymes.

中文翻译：

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设计用于从香叶醇生产 （R）-香茅醛的自给自足全细胞级联反应


（R）-香茅醛是高价值化学品的关键手性前体，例如最畅销的风味化合物 （−）-薄荷醇;然而，常规合成的产量低，对映选择性不令人满意。在这项研究中，我们开发了一种高原子效率的借氢级联反应，用于使用大肠杆菌 K12 的醇脱氢酶 （AdhP） 和酿酒酵母 YJM1341 （OYE2p） 的烯还原酶从香叶醇合成 （R）-香茅醛。关键限速酶 AdhP 进行结构引导的半合理工程，获得三重突变体 AdhP^{260T/284A/268P} （M3），其对香叶醇的催化效率 （k_cat/K_m） 提高了 1.28 倍。优化反应条件后，借氢复叠系统实现了 23.14 g/L 香叶醇向 （R）-香茅醛的转化，转化率为 98.23%，ee为 96.7%。这项工作代表了一种在不牺牲共底物或其他酶的情况下生物合成 （R） -香茅醛的替代方法。