Further structural studies of anti-complementary acidic heteroglycans from the leaves of Panax ginseng C.A. Meyer.

The three potent anti-complementary polysaccharides, GL-PI, GL-PII, and GL-PIV, isolated from the leaves of Panax ginseng C. A. Meyer, were subjected to base-catalysed beta-elimination in the presence of sodium borodeuteride or enzymic digestion with endo-alpha-D-(1----4)-polygalacturonase. beta-Eliminative degradation of GL-PI and GL-PII each gave neutral (IN and IIN) and acidic (IA and IIA) fractions. Each fraction N consisted of Ara, Rha, Gal, and Glc, whereas each fraction A comprised a large proportion of GalA in addition to Rha, Gal, Glc, and GLcA. Methylation analysis and g.l.c.-m.s. showed that each fraction IN and IIN contained Rha-(1----2)-Rha-ol-1-d, Rha-(1----4)-Rha-ol-1-d, Ara-(1----4)-Rha-ol-1-d, Gal-(1----4)-Rha-ol-1-d, Gal-(1----6)-Gal-ol-1-d, and GlcA-(1----4)-Rha-ol-1-d, and that IA and IIA contained Rha----Rha-ol-1-d, HexA----Rha-ol-1-d, and HexA----Rha----Rha-ol-1-d. Methylation analysis indicated that IN and IIN also contained high-molecular-weight 6-linked galactan and 4-linked glucan, and that IA and IIA consisted mainly of 2-linked Rha, 4-linked GalA, and terminal and 6-linked Gal. IIA contained more 2-linked Rha than IA. Endo-alpha-D-(1----4)-polygalacturonase-mediated digestion of GL-PIV produced a high-molecular-weight fraction (PG-1) which was rich in neutral sugars, fragments of intermediate size (PG-2), and oligosaccharides (PG-3). PG-1 contained a rhamnogalacturonan core, galactan (which mainly comprised terminal, 6-linked, and 4,6-disubstituted Gal), and 4-linked glucans. PG-2 contained (1----4)-linked alpha-galacturonan partially branched at position 2 or 3 and a rhamnogalacturonan core in addition to small proportions of Gal and Glc. PG-3 contained large proportions of oligogalacturonides.