Semisynthetic Isomers of Fucosylated Chondroitin Sulfate Polysaccharides with Fucosyl Branches at a Non-Natural Site.

The several interesting activities detected for fucosylated chondroitin sulfate (fCS) have fueled in the last years several efforts toward the obtainment of fCS oligosaccharides and low molecular weight (LMW) polysaccharides with a well-defined structure, in order to avoid the problems associated with the potential employment of native, sea cucumber sourced fCSs as a drug. Total synthesis and controlled depolymerization of the natural fCS polysaccharides are the main approaches to this aim; nonetheless, they present some limitations. These could be circumvented by semisynthesis, a strategy relying upon the regioselective fucosylation and sulfation of a microbial sourced polysaccharide sharing the same chondroitin backbone of fCS but devoid of any fucose (Fuc) and sulfate decoration on it. This approach is highly versatile, as it could open access also to fCS isomers carrying Fuc and sulfate groups at non-natural sites. Here we prepare for the first time some structurally homogeneous fCS isomers through a multistep procedure with a glycosylation reaction between a LMW polysaccharide acceptor and three different Fuc donors as key step. The obtained products were subjected to a detailed structural characterization by 2D-NMR. The conformational behavior was also investigated by NMR and molecular dynamics simulation methods and compared with data reported for natural fCS.