Site-selective Catalysis in Unprotected Carbohydrates

In recent years, the application of homogeneous catalysis methods for the functionalisation of complex molecules has seen a steep increase. The modification of complex molecules, most often drugs or natural products, can be very versatile, in particular when the parent compound is available, because it avoids the execution of an entire synthesis route. Nevertheless it poses high demands on the catalysis involved. In carbohydrate chemistry, this approach receives considerable attention as well,[1] also because many (oligo)saccharides are available from nature, though not always in substantial amounts. The challenge here is to discriminate between the (very) similar hydroxyl groups. In our group we focus on the site-selective catalytic oxidation[2] and photo-redox catalysis[3] of unprotected carbohydrates. Oxidation, because a carbonyl function is a versatile starting point for further functionalisation. And photocatalysis, because radical chemistry is mostly compatible with protic solvents and the present hydroxyl groups. Studies have focussed until now mainly on monosaccharides but also results on oligosaccharides[4] will be discussed as it is here where chemical biology can profit the most from this approach.