Carbohydrate Polymers 92 (2013) 704–711 Contents lists available at SciVerse ScienceDirect Carbohydrate Polymers jou rn al hom epa ge: www.elsevier.com/locate/carbpol Structural studies of an immunostimulating gluco-arabinan from seeds of Caesalpinia bonduc Eshita Kar Mandal a , Soumitra Mandal a , Saikat Maity a , Birendra Behera b , Tapas K. Maiti b , Syed S. Islam a,∗ a Department of Chemistry and Chemical Technology, Vidyasagar University, Midnapore 721102, West Bengal, India b Department of Biotechnology, Indian Institute of Technology (IIT) Kharagpur, Kharagpur 721302, West Bengal, India a r t i c l e i n f o Article history: Received 6 June 2012 Received in revised form 8 August 2012 Accepted 25 August 2012 Available online 1 September 2012 Keywords: Caesalpinia bonduc Seed Gluco-arabinan Structure NMR spectroscopy Immunostimulation a b s t r a c t 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-Glcp, (1→4)-Glcp, (1→2,3)-Glcp, T-Araf, (1→5)-Araf, (1→2,5)-Araf, and (1→2,3,5)-Araf 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)--d-glucopyranose followed by four (1→5)--l-arabinofuranose residues. In case of two (1→3)--d-glucopyranose, branching occurs at O-2 by a same residue terminated by another one at O-4 position. Out of four (1→5)- -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)- -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 sim- ilar extent of splenocytes and thymocytes stimulation, but arabinan showed appreciable macrophage activations. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction Caesalpinia bonduc (Nata Karanja) is an important medicinal plant (Anonymous, 1956; Gamble, 1967; Kapoor, 2005) and the seeds (Prajapati et al., 2006) are well known as nickernut. Two water-soluble fractions (PS-I and PS-II) were isolated from alkaline extract of endosperm of seeds of C. bonduc. The first fraction, PS-I was identified as arabinan and reported in Carbohydrate Polymers (Mandal et al., 2011). The second fraction, PS-II was characterized as gluco-arabinan; detailed structural studies of which revealed that the arabinan part of the gluco-arabinan molecule is exactly the same with the repeating unit of the previously reported arabinan (PS-I) and the linkages of the other glucosyl moieties attached to it were assigned and the structure was established. With a view to develop carbohydrate-based drugs, some immunostimulating ∗ Corresponding author. Tel.: +91 3222 276558x437/9932629971; fax: +91 3222 275329. E-mail address: sirajul 1999@yahoo.com (S.S. Islam). properties like splenocyte, thymocyte, and macrophage activations of both the molecules were studied and compared. 2. Materials and methods 2.1. Isolation, fractionation, and purification of the crude polysaccharide The endosperm of seeds of C. bonduc was boiled with 4% NaOH for 90 min, kept overnight at 4 ◦ C and filtered. The crude polysac- charide was isolated and purified by the method described earlier (Mandal et al., 2011). Crude material (210 mg) on fractionation through Sepharose 6B yielded two homogeneous PS-I, 55 mg and PS-II, 45 mg. The fractionation and purifications steps are shown in the following diagram. 0144-8617/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbpol.2012.08.093