Acetylation and methylation of homogalacturonans. 1. Optimisation of the reaction and characterisation of the products
1999
Renard, C.M.G.C. | Jarvis, M.C.
Tetrabutylammonium (TBA) salts of homogalacturonans, obtained by acid hydrolysis of demethylated citrus pectins, were acetylated and/or methylated. Methylation took place in DMSO, using CH(3)I as the reagent, and was stoichiometric up to a degree of methylation (DM) of >60. The best acetylation results, with acetic anhydride as reagent, were obtained using formamide as solvent and pyridine as catalyst, giving degrees of acetylation (DAc) of up to 150% in a single step. The reaction was fast but demanded large excess of acetic anhydride. Acetylation occurred on both the O-2 and the O-3 position, with a slight preference for O-2, of galacturonic acid residues. The hydrodynamic volume of the molecules showed little change after derivatisation. Acetylation inhibited hydrolysis of homogalacturonans by endopolygalacturonase.
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