Indoxylic Acid Esters as Convenient Intermediates Towards Indoxyl Glycosides

Indoxylic acid methyl and allyl esters with varied halide-substitution patterns were obtained in excellent yields using a scalable route. Phase-transfer glycosylation of these key intermediates was carried out with various glycosyl halides. Subsequent mild silver-mediated decarboxylation followed by Zemplen deacetylation led to indoxyl glycosides in good overall yields. Indoxyl glycosides are well-established and widely used tools for enzyme screening and enzyme-activity monitoring. In the past, their synthesis has been difficult, so this new approach has led to a variety of useful structures.