A Rapid and Mild Sulfation Strategy Reveals Conformational Preferences in Therapeutically Relevant Sulfated Xylooligosaccharides

Although sulfated xylooligosaccharides are promising therapeutic leads for a multitude of afflictions, the structural complexity and heterogeneity of commercially deployed forms (e. g. Pentosan polysulfate 1) complicates their path to further clinical development. We describe herein the synthesis of the largest homogeneous persulfated xylooligomers prepared to date, comprising up to eight xylose residues, as standards for biological studies. Near quantitative sulfation was accomplished using a remarkably mild and operationally simple protocol which avoids the need for high temperatures and a large excess of the sulfating reagent. Moreover, the sulfated xylooligomer standards so obtained enabled definitive identification of a pyridinium contaminant in a sample of a commercially prepared Pentosan drug and provided significant insights into the conformational preferences of the constituent persulfated monosaccharide residues. As the spatial distribution of sulfates is a key determinant of the binding of sulfated oligosaccharides to endogenous targets, these findings have broad implications for the advancement of Pentosan‐based treatments. Preparation of the largest homogeneous persulfated xylooligomers reported to date is facilitated by a rapid and quantitative one‐pot sulfation protocol based on the in situ generation of SO3 ⋅ DMF. The synthesized oligosaccharide standards afforded unique structural insights into persulfated xylooligomers, including a 1C4 conformational preference for all associated non‐reducing pyranosyl residues. Application of the method to the synthesis of a sulfated pyridyl‐α‐xylotriose also enabled identification of a pyridinium contaminant in a commercial sample of pentosan polysulfate, a widely‐deployed sulfated xylooligosaccharide‐based therapy.