[3)-alpha-D-Fucp4N,NAc-(1->4)-alpha-D-GalpA-(1->3)-alpha-D-GalpA-(1->]n
[3)-alpha-d-fucp4n,nac-(1->4)-alpha-d-galpa-(1->3)-alpha-d-galpa-(1->]n
A polysaccharide derivative comprising a trisaccharide repeating unit consisting of 2-acetamido-4-amino-2,4-dideoxy-α-<small>D</small>-fucose and two α-<small>D</small>-galacturonic acid residues linked sequentially (1→4) and (1→3) and with the trisaccharide repeats themselves being linked (1→3); corresponds to the serotype 1 capsular polysaccharide (CPS) of <em>Streptococcus pneumoniae</em>.