Laccase-mediated synthesis of novel substituted phenoxazine chromophores featuring tuneable water solubility.

Laccases are members of the blue copper oxidases family found in nature. They commonly oxidise a wide range of phenol and aniline derivatives, which in turn are involved in oxidative coupling reactions. Yet, laccases remain rarely described as biocatalysts in organic synthesis. This paper describes the chemical preparation of original sulfonated aminophenol substrates and their enzyme-mediated dimerisation into phenoxazine chromophores that feature tuneable water solubility as a function of the sulfonyl substituent. The scope and limitations of the biocatalysed synthetic process are outlined. Kinetic data were collected to evaluate the influence of physicochemical parameters. The structure of the novel phenoxazine dyes ("head-to-head" or "head-to-tail" dimer) was assessed by NMR spectroscopic analysis. Two crystalline compounds were analysed by X-ray diffraction. Such laccase-mediated synthesis (a green chemistry process) was proven to be more efficient than the chemical oxidation of o-aminophenols with silver oxide.