Ophiopogonpolysaccharide (OPS) was extracted by water decoction and ethanol precipitation, purified through eliminating protein by trichloroacetic acid method and column chromatography of DEAE-Cellulose-52, then sulfatedly modified by chlorosulfonic acid-pyridine method according to three-factors, ratio of chlorosulfonic acid to pyridine, reaction temperature and reaction time, and three level L₉(3⁴) orthogonal designed to obtain nine sulfated OPSs, sOPS₁-sOPS₉. Their effects on NDV to infect chick embryo fibroblast were compared by MTT assay taking the non-modified OPS as control. The results showed that sulfation modification could significantly enhance the antiviral activity of OPS, sOPS₃ presented best effect and the optimal modification conditions were the ratio of chlorosulfonic acid to pyridine of 1:4, the reaction temperature of 60 °C and the reaction time of 2 h.
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