Structural characterization of a heteropolysaccharide isolated from hot water extract of the stems of Amaranthus tricolor Linn. (Amaranthus gangeticus L.)

A water-soluble polysaccharide (PS-I), isolated from the aqueous extract of the stems of Amaranthus tricolor Linn. (Amaranthus gangeticus L.), was found to consist of l-arabinose, methyl-d-galacturonate, d-galactose, and 3-O-Ac-l-rhamnose in a molar ratio of nearly 1:1:1:1. On the basis of total acid hydrolysis, methylation analysis, periodate oxidation, and NMR studies (¹H, ¹³C, TOCSY, DQF-COSY, NOESY, ROESY, HMQC, and HMBC), the structure of the repeating unit of the PS-I is determined as: