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Structural features of the four anti-complementary polysaccharides (PA-IIa-1, PA-IIa-2, PA-IIa-3, and HPA-IVa) isolated from bracken were investigated. No change in λ_(max) of Congo Red in the presence of these polysaccharides indicated that they did not form helical structures but were highly branched polymers. Based on the H-1 signals of α- and β-anomers at 5.15∼5.67 p.p.m. and 4.63∼4.99 p.p.m. in their ¹H-NMR spectra, it is suggested that they all have both α- and β-configuration in the anomerization of the glycosidic linkages. They also showed C-1 signals of α- and β-anomers at 99.5∼102.0 p.p.m. and 103.2∼104.5 p.p.m, in the ^(13)C-NMR spectra. Unlike the other three polysaccharides PA-IIa-1 did not exhibit acetyl signal (¹H, 2.30-2.42 p.p.m.; ^(13)C, 21.64∼21.70 p.p.m.) in the component sugar residues. Methylation analysis revealed that high proportion of terminal Galp, 4-linked Xylp and 2-linked Fucf was contained in all polysaccharides. HPA-IVa contained the highest 4-linked Xylp and 5-linked Xylf, whereas PA-IIa-1, PA-IIa-2, and PA-IIa-3 had higher termianal Galp than HPA-IVa. Most polysaccharides possessed 2-linked Manp and 2, 4-disubstituted Manp at the same ratio, whereas PA-IIa-3, which had the lowest anti-complementary activity, contained much higher proportion of 2-linked Manp (8.1 ㏖%) than 2,4-disubstituted Manp (2.8 ㏖%).
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