The red alga Botryocladia occidentalis presents three distinct fractions of sulfated polysaccharides. The elucidation of structures of various B. occidentalis fractions has been explored in prior research. In this study, the first fraction with the least sulfation underwent NMR structure elucidation. Additionally, this sulfated polysaccharide underwent analysis following chemical modifications. Findings have unveiled the presence of both 4-linked α- and 3-linked β-galactose units with the following chemical characteristics: over half of the total galactose units are unsulfated, the α-units are primarily 3,6-anhydrogalactose units either 2-O-methylated or 2-O-sulfated, and the β-galactose units can be 4-O-sulfated or 2,4-O-disulfated. Results from SPR-based assays demonstrated stronger binding of the least sulfated galactan to heparin cofactor II, yet weaker binding to thrombin, factor Xa, and antithrombin compared to unfractionated heparin. This study, combined with our previous publication, concludes the structural characterization of the three polysaccharides present in the cell wall of B. occidentalis and elucidates the relationship between their constituent chemical groups and their interactions with blood co-factors
