Laccase initiated C-C couplings: Various techniques for reaction monitoring

In this study the fungal laccase from Myceliophthora thermophila (Novozym (R) 51003) was investigated for oxidative C-C couplings of phenolic compounds. This enzyme requires only molecular oxygen as oxidant, which represents a great advantage for oxidative coupling reactions. However, such couplings are typically considered as highly unselective, due to the radical reaction mechanism of laccases. Based on different analytical techniques we gained detailed insights into laccase initiated coupling reactions. A preselection of potential substrates was realized via oxygen measurement during laccase initiated oxidations. Furthermore in situ FT-IR spectroscopy facilitated analyses in-depth, due to feasibility to detect dissolved as well as solid compounds. This technique allowed the detection of the grade of couplings of various laccase substrates, depending on different conditions. As a result oxidative dimerizations of 2,6-disubstituted phenols could be identified as highly selective and were scaled-up to multigram scale. Thereby the oxidation product of 2,6-diisopropyl phenol can be easily reduced to the corresponding biphenol, the antibacterial agent dipropofol. The presented techniques open up new biocatalytical approaches receiving quinoid units as key elements of many natural compounds and pharmaceuticals. (C) 2015 Elsevier Ltd. All rights reserved.