Synthesis of Indigo-Dyes from Indole Derivatives by Unspecific Peroxygenases and Their Application for In-Situ Dyeing

Tyrian purple (also known as royal or imperial purple) is the oldest known commercial pigment and still one of the most expensive dyes, often associated with the wardrobes of clergy and royalty. It is a brominated derivative of indigo, a natural dye that has been used since 4000 BC. Moreover, just recently, the therapeutic value of indigoids for the treatment of several disorders was discovered. The manufacturing of indigo derivatives by the existing chemical routes has become increasingly uninteresting due to the use of aggressive reagents, expensive starting materials and high-energy costs. Thus, both dyestuff manufacturers and the pharmaceutical industry are interested in the development of gentle preparation methods of indigoids from simple precursors. Here, we describe a simple enzymatic method for the one-step synthesis of Tyrian purple and other indigo derivatives with fungal peroxygenases (UPO, EC 1.11.2.1). The reaction does not require complex co-substrates and works well in phosphate buffers with H2O2 (<0.1 wt%) and less than 5% (v/v) acetonitrile as co-solvent. We demonstrate the scaling up of the reaction to 10 Liters and established thereupon an environmentally friendly combined synthesis and in-situ dyeing process, further simplifying the manufacturing of vat-dyed fabrics. Eventually, we screened a number of halogen-substituted indoles in the search for novel indigo derivatives, which may be of interest for pharmaceutical and/or dyeing purposes.