Phenoloxidase catalyzed coupling of catechols. Identification of novel coupling products.

Phenoloxidases from insect cuticle as well as from other sources oxidize catechols resulting in the formation of various coupling products. The two dominating products from 4-methylcatechol and the main product from N-acetyldopamine were purified and identified by means of plasma desorption and electron impact mass spectrometry and by 1H- and 13C-NMR spectroscopy. The main product from both catechols has a quinoid trihydroxybiphenyl structure, indicating oxidative coupling between a catechol and the corresponding trihydroxy derivative. The second product from 4-methylcatechol is a biphenyltetrol derivative, indicating oxidative coupling between two catechols.