Add time:08/27/2019         Source:sciencedirect.com

Evidence for the anomeric configurations and attachment sites of 3-deoxy-d-lyxo-2-heptulosaric acid (DHA) and apiosyl residues have been obtained through the characterization of two oligoglycosyl fragments isolated from rhamnogalacturonan II (RG-II). One of the oligoglycosyl fragments, a pentaglycosyl aldonic acid generated by Smith degradation of RG-II, was composed of four d-galactopyranosyluronic acid residues, a DHA residue, and a threonic acid residue (derived from a d-galactopyranosyluronic acid residue). The structural analysis of the pentaglycosyl aldonic acid established the β-d-configuration for the DHA residue. Furthermore, it established that a previously identified diglycosyl side chain, 5-O-(β-l-arabinofuranosyl)-DHA was directly attached to O-3 of a d-galactopyranosyluronic acid residue in the backbone of RG-II. The second oligoglycosyl fragment, a peralkylated diglycosyl hex-1-enitol, was generated by hex-5-enose degradation of permethylated and carboxyl-reduced RG-II. The structure of the peralkylated diglycosyl hex-1-enitol, β-l-Rhap-(1→3′)-β-d-Apif-(1→5)-hex-1-enitol, was determined by a combination of glycosyl-linkage composition analysis and n.m.r. spectroscopy. The n.m.r. data indicated the β-configuration for the d-apiosyl residue. The isolation and characterization of the diglycosyl hex-1-enitol also established that a previously identified heptaglycosyl side chain was directly attached to O-2 of a d-galactopyranosyluronic acid in the backbone of RG-II.

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