STRUCTURAL CHARACTERIZATION OF 2 OLIGOSACCHARIDE FRAGMENTS FORMED BY THE SELECTIVE CLEAVAGE OF RHAMNOGALACTURONAN-2 - EVIDENCE FOR THE ANOMERIC CONFIGURATION AND ATTACHMENT SITES OF APIOSE AND 3-DEOXY-2-HEPTULOSARIC ACID

Evidence for the anomeric configurations and attachment sites of 3-deoxy-D-lyxo-2-heptulosaric acid (DHA) and apiosyl residues has 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 beta-D-configuration for the DHA residue. Furthermore, it established that a previously identified diglycosyl side chain, 5-O-(beta-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 digtycosyl 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, beta-L-Rhap-(1 --> 3')-beta-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 beta-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.