Chemical modifications of algal mannans and xylomannans: effects on antiviral activity.

The structures of two sulfated xylomannans extracted from the red alga Nemalion helminthoides were determined. These two fractions plus a sulfated mannan, isolated from the same alga and whose structure was previously reported, were subjected to chemical modification. The mannan was oversulfated with SO(3)-pyridine in dimethyl sulfoxide at 60 °C during two and three hours and the xylomannans were subjected to Smith degradation in order to eliminate xylose side-chains. Structural analysis of all derivatives was carried out by methylation analysis and (13)C NMR spectroscopy. Antiviral activity against herpes simplex virus type 1 and 2, and dengue virus type 2 of native and modified mannans and xylomannans was estimated. Anticoagulant effect of the active fractions was also determined.