Selective cleavage of welan gum (S-130) by oxidative decarboxylation with lead tetraacetate

Oxidative decarboxylation of peracetylated welan gum (S-130)_ with lead tetraacetate resulted in selective cleavage of the glucuronosidic linkages. Products of the degradation were reduced with sodium borohydride, O-deacetylated, and fractionated. Polymeric and oligomeric fractions were separated and analysed by 1H NMR spectroscopy and fast atom bombardment mass spectrometry, and were found to be monomers, dimers, and trimers of the repeating unit. Results show that this method may be used to liberate alditol-terminated multiples of the repeating unit of peracetylated glycuronans by cleavage and degradation of the uronic acid residues. The reaction sequence also confirms the recent finding that welan gum contains repeating units with randomly distributed terminal groups.