NMR structural elucidation of the arabinan from Prunus dulcis immunobiological active pectic polysaccharides

Abstract

The structure of the arabinan moiety of a purified arabinan-rich pectic polysaccharide from the cell walls of Prunus dulcis seeds was investigated by NMR spectroscopy. This polymer, which is able to induce a lymphocyte stimulatory effect, had an arabinan glycosidiclinkage composed of T-Araf: (1→5)-Araf: (1→3,5)-Araf: (1→2,3,5)-Araf in the relative proportions of approximately 3:2:1:1. Based on the ¹H, ¹³C, COSYPR, gHSQC and gHMBC spectra of analysed arabinan, a tentative structure is presented, showing that it is composed by a very branched and, possibly, repetitive structure of seven residues. The observed (1→5) direct linkage between (1→2,3,5)- Araf and (1→3,5)-Araf residues support the occurrence of these contiguous branched residues in the arabinan backbone.