Chondroitin sulfate (CS) is a glycosaminoglycan playing several biological functions, which seem to be encoded through its sulfation pattern. This "sulfation code" is still to be deciphered. One of the barriers to this goal is the difficulty in achieving structurally well-defined CS polysaccharides since extraction from natural sources often leads to complex heterogeneous structures. Instead, an approach relying on chemical modification of a microbially sourced unsulfated chondroitin can allow access to semisynthetic CS polysaccharides with a well-defined sulfation pattern. We report herein some new, suitably developed chemical strategies affording CSs with unprecedented sulfation patterns, carrying a single sulfate group regioselectively placed at either C-2 or C-3 position of the glucuronic acid residues or at both sites. In this way, all the possible variants of CS sulfation patterns can be now accessed. This will allow more detailed and complete structure−activity relationship investigations of CS biological functions and applications.

Fucosylated chondroitin sulfate (fCS) is a glycosaminoglycan found up to now exclusively in the body wall of sea cucumbers. It shows several interesting activities, with the anticoagulant and antithrombotic as the most attractive ones. Its different mechanism of action on the blood coagulation cascade with respect to heparin and the retention of its activity by oral administration make fCS a very promising anticoagulant drug candidate for heparin replacement. Nonetheless, its typically heterogeneous structure, the detection of some adverse effects and the preference for new drugs not sourced from animal tissues, explain how mandatory is to open an access to safer and less heterogeneous non-natural fCS species. Here we contribute to this aim by investigating a suitable chemical strategy to obtain a regioisomer of the natural fCS polysaccharide, with sulfated l-fucosyl branches placed at position O-6 of N-acetyl-d-galactosamine (GalNAc) units instead of O-3 of d-glucuronic acid (GlcA) ones, as in natural fCSs. This strategy is based on the structural modification of a microbial sourced chondroitin polysaccharide by regioselective insertion of fucosyl branches and sulfate groups on its polymeric structure. A preliminary in vitro evaluation of the anticoagulant activity of three of such semi-synthetic fCS analogues is also reported.been the most intensely studied in the last two decades. It attracted a constantly increasing interest for its activity in biological events related to inflammation, hyperglycemia, atherosclerosis, cellular growth, cancer metastasis, angiogenesis, and, above all, coagulation and thrombosis [2]. The anticoagulant and antithrombotic activity is observed also on antithrombin (AT) and heparin cofactor II (HC-II)-free plasmas, for which the most widespread and long-term used anticoagulant drug-unfractionated heparin-is inactive, due to some differences in the mechanism of action of fCS on the blood coagulation cascade [3,4]. Furthermore, oral administration of fCS retains its activity, because it is digested neither during its adsorption in the gastrointestinal tract nor by intestinal bacterial enzymes [5]. These features make fCS a very promising anticoagulant drug candidate for heparin replacement [6].From a structural point of view, fCS shares the same linear core backbone as chondroitin sulfate (CS) polysaccharide, with alternating N-acetyl-d-galactosamine (GalNAc) and d-glucuronic acid (GlcA) residues linked together through alternating β-1→3 and β-1→4 glycosidic bonds and sulfated to a different extent on their hydroxyls. The unique structural peculiarity of fCSs is the additional presence of variously sulfated fucose (Fuc) branches [7,8], which are essential for the observed biological activities [9][10][11]. Very often the branches are constituted of a single Fuc unit α-glycosidically linked at O-3 site of GlcA residues. Nonetheless, fCSs from some sea cucumbers species with slightly different structural features have also been found [12]. Indeed, Ludwigothurea grisea [13], Eupentacta f...

Symmetrical diglycosyl-selenides or diselenides can be readily prepared with high chemoselectivity by direct use of elemen-tary selenium as a cheap selenating agent (reduced in situ by sodium borohydride), and glycosyl...

Controlling chondroitin sulfates (CSs) biological functions to exploit their interesting potential biomedical applications requires a comprehensive understanding of how the specific sulfate distribution along the polysaccharide backbone can impact in their biological activities, a still challenging issue. To this aim, herein, we have applied an “holistic approach” recently developed by us to look globally how a specific sulfate distribution within CS disaccharide epitopes can direct the binding of these polysaccharides to growth factors. To do this, we have analyzed several polysaccharides of marine origin and semi-synthetic polysaccharides, the latter to isolate the structure-activity relationships of their rare, and even unnatural, sulfated disaccharide epitopes. SPR studies revealed that all the tested polysaccharides bind to FGF-2 (with exception of CS-8, CS-12 and CS-13) according to a model in which the CSs first form a weak complex with the protein, which is followed by maturation to tight binding with kD ranging affinities from ~1.31 μM to 130 μM for the first step and from ~3.88 μM to 1.8 nM for the second one. These binding capacities are, interestingly, related with the surface charge of the 3D-structure that is modulated by the particular sulfate distribution within the disaccharide repeating-units.

Synthesis of the threonine-decorated tetrasaccharide repeating unit of a cryoprotectant polysaccharide with a glycosaminoglycan-like structure.