Glycosylated Eumelanin Building Blocks by Thioglycosylation of 5,6-Diacetoxyindole with an Expedient Selenium-Based Dynamic-Mixture Methodology

A series of 3-thioglycosylated 5,6-diacetoxyindole derivatives, which are important tools for eumelanin research and application, were prepared through a practical and efficient approach exploiting a dynamic mixture of thioglycoside agents. The strategy is feasible for installing both mono- and disaccharide units and relies on the facile in situ conversion of glycosyl disulfides into the corresponding, more reactive, phenylselenenyl sulfides in the presence of diphenyl diselenide, N-bromosuccinimide (NBS) and tetrabutylammonium bromide (TBAB).