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<p>Biocatalysis contributes significantly to the development of more sustainable synthetic pathways by using mild reaction conditions and water as a solvent. However, many relevant classes of compounds, including privileged groups in drug design, are not yet accessible via enzymatic pathways. In this context, the development of an enzymatic route to indazoles remains an unmet challenge. Here, we present a nitroreductase-triggered indazole formation, in which 2-nitrobenzylamine derivatives are converted to reactive nitrosobenzylamine intermediates that spontaneously cyclize and aromatize to indazoles. Two nitroreductases accept a series of 2-nitrobenzylamine derivatives with excellent conversions (up to &gt;99&#xa0;%). In the case of <i>N</i>-substituted nitrosobenzylamines, 2<i>H</i>-indazoles are formed, whereas other derivatives led to 1<i>H</i>-indazoles. The synthetic value of the nitroreductase-triggered indazole formation is further demonstrated by successful coupling with an imine reductase in a sequential cascade reaction on a 50 mg scale. With this cascade, 2<i>H</i>-indazoles are accessible from cheap 2-nitrobenzaldehyde and primary amines, resulting in up to 85&#xa0;% conversion and 68&#xa0;% isolated yield.</p>

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Nitroreductase-triggered indazole formation

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2026年2月2日

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  • Henrik Terholsen,
  • Lisa Medema,
  • Elizaveta Chernyshova,
  • Alejandro Prats Luján,
  • Gerrit J. Poelarends,
  • Sandy Schmidt

摘要

Biocatalysis contributes significantly to the development of more sustainable synthetic pathways by using mild reaction conditions and water as a solvent. However, many relevant classes of compounds, including privileged groups in drug design, are not yet accessible via enzymatic pathways. In this context, the development of an enzymatic route to indazoles remains an unmet challenge. Here, we present a nitroreductase-triggered indazole formation, in which 2-nitrobenzylamine derivatives are converted to reactive nitrosobenzylamine intermediates that spontaneously cyclize and aromatize to indazoles. Two nitroreductases accept a series of 2-nitrobenzylamine derivatives with excellent conversions (up to >99 %). In the case of N-substituted nitrosobenzylamines, 2H-indazoles are formed, whereas other derivatives led to 1H-indazoles. The synthetic value of the nitroreductase-triggered indazole formation is further demonstrated by successful coupling with an imine reductase in a sequential cascade reaction on a 50 mg scale. With this cascade, 2H-indazoles are accessible from cheap 2-nitrobenzaldehyde and primary amines, resulting in up to 85 % conversion and 68 % isolated yield.