Structure and potential immunological activity of a pectin from Centella asiatica (L.) Urban

S3A was a RG-I pectin isolated from Centella asiatica that contained Rha, Ara, Gal, Glc and GalA in molar ratio of 1.0:0.6:1.5:0.2:1.1 and had been found to have a backbone composed mainly of the disaccharide repeat unit, -->4)-alpha-D-GalpA-(1-->2)-alpha-L-Rhap-(1-->. Based on methylation analysis, NaIO4 oxidation, partial acid hydrolysis and lithium-treatment, the structural features were elucidated. Side chains of S3A were predominantly linked to O-4 of 1,2,4-linked alpha-L-Rhap. The side chains are comprised of arabinosyl chains, galactosyl chains, arabinogalactosyl chains and short glucosyl chains. A total of 45% Rhap in the backbone was substituted by side chains. The arabinosyl residues were mostly distributed in the arabinosyl side chains. According to the immunological results of S3A and its degraded derivatives, S3A had no immunological activity, but its derivatives had immuno-stimulating activities to some extent.