Structural studies of S-7, another exocellular polysaccharide containing 2-deoxy-arabino-hexuronic acid

The exocellular polysaccharide S-7, a heteropolysaccharide from Azotobacter indicus var. myxogenes has been studied using methylation analysis, Smith degradation, partial acid hydrolysis, NMR spectroscopy and mass spectrometry as the principal methods. It is concluded that the repeating unit has the following structure: [structure: see text] The absolute configuration of the deoxyhexuronic acid was deduced from 1H NMR chemical shifts and is most likely D. Approximately two O-acetyl groups per repeating unit are present, one of which is presumably on the Rha residue. The structure bears great resemblance to another polysaccharide, recently studied, produced by Sphingomonas paucimobilis I-886.