Sulfated Polysaccharides from green seaweeds of the Bryopsidales

CIANCIA, MARINA; CANELÓN, DILSIA; SUAREZ, ALÍRICA ; COMPAGNONE, REYNALDO ; ARATA, PAULA XIMENA; FERNÁNDEZ, PAULA VIRGINIA

Nantes

Workshop; Plant and Seaweed Polysaccharide Workshop; 2012

INRA, CNRS (Francia)

Green seaweeds of the Bryopsidales group biosynthesize sulfated polysaccharides, mainly constituted by galactose and/or arabinose, and, sometimes also xylose. Those of Codium have been studied in detail. For C. vermilara, it has been shown that the major sulfated polysaccharides are a -(13)-D-galactan, partially sulfated mostly on C-4, and a highly ramified on C-6. Important amounts of terminal -D-galactose units substituted with pyruvic acid forming a 5-membered ketal with C-3 and C-4 are present (R configuration), similar galactans were isolated and characterized from other species of this genus. The other sulfated polysaccharide is a linear pyranosic -(13)-L-arabinan, mainly constituted by disulfated units. The degree of sulfation of this polysaccharide varies for different fractions. A third sulfated polysaccharide was found. It is a -(14)-D-mannan, with a backbone similar to that of the major fibrillar wall component for this species, but sulfated mostly on C-2 of some of the units. Although Bryopsis belongs to the same suborder as Codium, the Bryopsidineae, the system of sulfated polysaccharides produced by this seaweed is quite different. The -(13)-D-galactan from B. plumosa is linear, sulfated mainly on C-6 of some galactose units, while others are substituted with pyruvic acid, but in this case linked to C-4 and C-6, giving a 6-membered ring (S configuration). In addition, a sulfated rhamnan and a furanosic arabinan structure were also detected in the water-soluble fractions. On the other hand, Penicillus capitatus and Udotea flabellum belong to the suborder Halimedineae, which comprises calcified seaweeds found in tropical and subtropical areas. Room temperature water extracts (PA and UA, respectively) showed galactose was the main sugar constituent, in both cases only trace amounts of arabinose were present. Fractionation of PA by anion exchange chromatography allowed to isolate two purified -(13)-D-galactans (F2 and F7) which differ in the proportion of different structural units, but both have side chains on C-6, very important amounts of pyruvic acid ketals (molar ratio Gal:S:Pyr, 1:0.43:0.51 and 1:0.65:0.27, respectively), which are forming a 6-membered ring with C-4 and C-6 of some of the galactose units. In conclusion, green seaweeds from the Bryopsidales synthesize 3(or 3,6)-linked -D-galactans with different substitution patterns with sulfate and pyruvic acid and different degrees of ramification. Many of these seaweeds also synthesize arabinans. Some of them are constituted by sulfated 3-linked -L-arabinopyranosyl residues, like those of C. vermilara. However, neutral furanosic arabinan structures were found in B. plumosa. Moreover, both structural types were detected in the water extracts from C. fragile.