Synthesis of type 1 Lewis b hexasaccharide antigen structures featuring flexible incorporation of l-[U-13C6]-fucose for NMR binding studies

Abstract

While ¹³C-labelled proteins are common tools in NMR studies, lack of access to ¹³C-labelled carbohydrate structures has restricted their use. L-Fucose is involved in a wide range of physiological and pathophysiological processes in mammalian organisms. Here, L-[U-¹³C₆]-Fuc labelled type I Lewis b (Le^b) structures have been synthesised for use in NMR binding studies with the Blood-group Antigen Binding Adhesin (BabA), a membrane-bound protein from the bacterium Helicobacter pylori. As part of this work, an efficient synthesis of a benzylated L-[U-¹³C₆]-Fuc thioglycoside donor from L-[U-¹³C₆]-Gal has been developed. The design and synthesis of an orthogonally protected tetrasaccharide precursor enabled controlled introduction of one or two ¹³C-labelled or non-labelled fucosyl residues prior to global deprotection. NMR analysis showed that it is straightforward to assign the anomeric centres as well as the H-5 positions to the individual fucosyl residues which are relevant for NMR binding studies.