A WATER-SOLUBLE ARABINOGALACTAN FROM THE FRUIT PULP OF AZADIRACHTA-INDICA

A water soluble arabinogalactan isolated from the fruit pulp of Azadirachta indica by cold water extraction after delipidification has [alpha]589.5 + 20.2-degrees + 20.2-degrees and contains D-galactose, L-arabinose, L-rhamnose and D-glucuronic acid in 6:9.2:1.1:1.6 molar ratio. The molecular weight of the arabinogalactan has been found to be 2.2 x 10(5) by gel permeation chromatography on Sepharose CL-4B. The methylation and periodate oxidation studies are in good agreement with the proposed stucture. On graded hydrolysis the native arabinogalactan furnishes one disaccharide, two trisaccharides and two tetrasaccharides. The anomeric configurations of the hexose residues have been determined by chromium trioxide oxidation. It has been established that the native heteropolysaccharide is a highly branches arabinogalactan having (1 --> 6)- and (1 --> 3)-beta-D-galactan backbone with further substitution at 0-3 and 0-6 respectively and with exceptionally high content of L-arabinosyl units as side chains where these units exhist not only as (1 --> 3) linked chains and terminal nonreducing arabinofuranosyi but also a small part of it is present as chain units of (1 --> 2) linked L-arabinofuranosyl and arabinopyranosyl units. It also contains D-glucuronic acid and its 4-0-methyl ether units mainly as nonreducing ends and L-rhamnopyranosyl units are present both as terminal and (1 --> 4) linked chain units.