Chlorination of anthraquinones by lichen and fungal enzymes

Chlorination of the anthraquinones, emodin and 7-chloroemodin, was studied with an enzyme preparation from the lichen Nephroma laevigatum, and a commerically available fungal chloroperoxidase (EC 1.11.1.10). The fungal enzyme converted emodin to a mixture of 5-chloro, 7-chloro and 5,7-dichloroemodin, while converting the 7-chloro isomer to 5,7-dichloroemodin in nearly quantitative yield. The lichen enzyme, however, chlorinated emodin only at C-7 and failed to chlorinate 7-chloroemodin further. In non-enzymic controls, emodin gave the same set of products as the fungal enzyme but 7-chloroemodin did not undergo further chlorination. The chemical structures of the products were confirmed from UV, EI-mass and H-1 NMR spectral data. Copyright (C) 1996 Elsevier Science Ltd