Development of Semisynthetic, Regioselective Pathways for Accessing the Missing Sulfation Patterns of Chondroitin Sulfate

Abstract

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.

A Study for the Access to a Semi-synthetic Regioisomer of Natural Fucosylated Chondroitin Sulfate with Fucosyl Branches on N-acetyl-Galactosamine Units

“…In particular, α-linked Fuc branches were almost exclusively found on fCS-ii and fCS-iii, as expected from the α-stereodirecting effect of DMF in fucosylations [46], whereas β-stereochemistry surprisingly prevailed on polysaccharide fCS-i obtained with a glycosylation at −30 • C. Evaluation of the weight-averaged molecular mass (M w ) and polydispersity for fCS-i-iii was performed by HP-SEC-TDA. They all showed a M w value that was rather lower (7.8-9.2 kDa) with respect to both starting E. coli sourced chondroitin (38 kDa) [55] and natural fCSs (55-65 kDa) [56]. This result was expected [55] due to the acid-mediated reactions (methyl esterification, benzylidene ring installation and cleavage as well as glycosylation) employed in the semi-synthetic strategy to fCS-i-iii.…”

“…They all showed a M w value that was rather lower (7.8-9.2 kDa) with respect to both starting E. coli sourced chondroitin (38 kDa) [55] and natural fCSs (55-65 kDa) [56]. This result was expected [55] due to the acid-mediated reactions (methyl esterification, benzylidene ring installation and cleavage as well as glycosylation) employed in the semi-synthetic strategy to fCS-i-iii.…”

Production and purification of higher molecular weight chondroitin by metabolically engineered Escherichia coli K4 strains

“…The chemical modification of biopolymers often requires harsh conditions that might reduce their molecular weight e.g. the conversion of chondroitin into CS 34 , 35 . Thereof, the production of chondroitin with higher Mw is interesting not only to investigate potential novel properties but also to facilitate the obtainment of its semi-synthetic derivatives.…”

(Semi)-Synthetic Fucosylated Chondroitin Sulfate Oligo- and Polysaccharides

“…To overcome these limitations, a new chondroitin acceptor (84, Scheme 8), obtained by mild hydrolysis of benzylidene residues of polysaccharide 82 without a significant cleavage of glycosidic bonds, was very recently employed for the regioselective insertion of Fuc branches at GalNAc O-6 site [74]. Furthermore, the semi-synthesis of low molecular weight fCS polysaccharides with Fuc units exclusively linked at GlcA O-3 positions-as in most of natural fCSs-has been very recently accessed [78]. This result was achieved by applying the one-pot 3,6-lactonization/benzoylation/lactone methanolysis sequence-already developed on di-, tetra-and hexasaccharide chondroitin derivatives (Schemes 5 and 6)-also on microbial sourced CS-0 polysaccharide in order to obtain a polymeric acceptor with a single, free hydroxyl per repeating unit exclusively placed at GlcA C-3 site [79].…”

“…Furthermore, the semi-synthesis of low molecular weight fCS polysaccharides with Fuc units exclusively linked at GlcA O-3 positions-as in most of natural fCSs-has been very recently accessed [78]. This result was achieved by applying the one-pot 3,6-lactonization/benzoylation/lactone methanolysis sequence-already developed on di-, tetra-and hexasaccharide chondroitin derivatives (Schemes 5 and 6)-also on microbial sourced CS-0 polysaccharide in order to obtain a polymeric acceptor with a single, free hydroxyl per repeating unit exclusively placed at GlcA C-3 site [79]. A small library of low molecular weight polysaccharides resembling fCS structure, but with Fuc branches linked to the polymeric backbone through amide instead of glycosidic linkages, was prepared starting from two differently sulfated CS polysaccharides (CS-A and CS-E) [80].…”