Structural studies of an immunostimulating gluco-arabinan from seeds of Caesalpinia bonduc.

Abstract A water-soluble gluco-arabinan (PS-II, M W  ∼ 62 kDa) isolated from the alkaline extract of the endosperm of Caesalpinia bonduc showed the presence of T-Glc p , (1→4)-Glc p , (1→2,3)-Glc p , T-Ara f , (1→5)-Ara f , (1→2,5)-Ara f , and (1→2,3,5)-Ara f in a relative proportion of approximately 2:2:2:3:2:1:1. The proposed repeating unit of the polysaccharide possessed a branched backbone of two (1→3)-α- d -glucopyranose followed by four (1→5)-α- l -arabinofuranose residues. In case of two (1→3)-α- d -glucopyranose, branching occurs at O -2 by a same residue terminated by another one at O -4 position. Out of four (1→5)-α- l -arabinofuranose residues, one residue is terminated at O -2 and O -3 by two arabinofuranose residues and another one situated at the adjacent position is terminated at O -2 with same residue, and two (1→5)-α- l -arabinofuranose residues are free from branching and located before and after the two branched arabinofuranose residues. This gluco-arabinan molecule and previously reported arabinan showed similar extent of splenocytes and thymocytes stimulation, but arabinan showed appreciable macrophage activations.