Indigoids represent natural product-based compounds applicable as organic semiconductors and photoresponsive materials. Yet modified indigo derivatives are difficult to access by chemical synthesis. Thus a biocatalytic approach applying several consecutive selective C-H functionalizations was developed that selectively provides access to various indigoids: Enzymatic halogenation of l-tryptophan followed by indole generation with tryptophanase yields 5-, 6- and 7-bromoindoles. Subsequent hydroxylation using a flavin monooxygenase furnishes dibromoindigo that is derivatized by acylation. This four-step one-pot cascade gives Boc-protected dibromoindigo in good isolated yields. The halogen substituent allows for late-stage diversification by cross-coupling directly performed in the crude mixture, thus enabling synthesis of 5,5'- and 6,6'-diarylindigo derivatives. This chemoenzymatic approach provides a modular platform towards novel indigoids with attractive spectral properties. © 2021 Wiley-VCH GmbH.
The document is publicly available on the WWW.