A sulfated heterorhamnan with novel structure isolated from the green alga Monostroma angicava

A sulfated polysaccharide, designated MAP2, was isolated from Monostroma angicava by water extraction, anion-exchange and size-exclusion chromatography. The structural characteristics of MAP2 were investigated by chemical and spectroscopic methods, including methylation analysis, one- and two-dimensional nuclear magnetic resonance and electrospray mass spectrometry with collision-induced dissociation spectroscopic analyses. The results showed that MAP2 was primarily composed of rhamnose with small amounts of xylose, glucuronic acid and glucose. The molecular weight of MAP2 was estimated to be about 671 kDa. The backbone of MAP2 was mainly constituted by 3-linked, 2-linked-á-l-rhamnose residues. Sulfate substitutions were at C-2/C-4 of 3-linked-á-l-rhamnose and C-3/C-4 of 2-linked-á-l-rhamnose residues. The branches consisted of 3-linked and 2-linked-á-l-rhamnose with monosulfate/unsulfate, as well as small amounts of β-d-GlcA-(1→ and β-d-GlcA (2SO₄)-(1 → . Minor amounts of →4)-d-Glcp-(1→ and β-d-Xylp (4SO₄)-(1→ might also be existent in MAP2. The investigation demonstrated that MAP2 was a novel sulfated rhamnan distinguishing from other algal sulfated rhamnans.