The preparation and susceptibility to hydrolysis of novel O-galacturonoyl derivatives of carbohydrates

d-Galacturonic acid or (1 → 4)-α-d-galacturonan reacted in aqueous pyridine in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide with alcohols to yield esters. The alcohols that gave high yields of d-galacturonoyl derivatives were primary and included methanol, ethanol, 1-propanol, d-glucose, d-galactose, methyl β-d-glucopyranoside, methyl β-d-galactopyranoside, and cellulose. d-Galacturonic acid itself readily gave an O-d-galacturonoyl-d-glacturonic acid. The proposed structure of one compound, methyl 6-O-d-galacturonoyl-β-d-glucopyranoside, was supported by ¹H and ¹³C NMR data and the FAB mass-spectral data. Each ester was hydrolysed at pH 11 and 25°C within 1 h. O-d-Galacturonoyl-d-glucose was considerably more alkali labile than O-polygalacturonoyl-d-glucose, and O-d-galacturonoylcellulose had an intermediate stability. The esters were relatively stable to cold acid, but could be hydrolysed by M trifluoroacetic acid at 100°C for 1 h. The esters tested were resistant to digestion by 'Driselase', although the glycosidic bonds of O-polygalacturonoyl-d-glucose were hydrolysed to yield O-oligogalacturonoyl-d-glucoses of low molecular weight. The possible application of these analytical methods to the detection of O-uronoyl-type cross-links in cell-wall polysaccharides is discussed.