Partially acetylated sucrose. Structures of hepta-O-acetylsucroses formed by deacetylation of octa-O-acetylsucrose

Abstract

Formation of hepta-O-acetylsucroses I, II, XI, and XII, having a free hydroxyl group on the fructose moiety, in deacetylation of octa-O-acetylsucrose on aluminum oxide impregnated by potassium carbonate was proved by preparative chromatography on silica gel and by liquid chromatography. Their structures were inferred from the 1H and 13C NMR spectra, from NMR and mass spectra of their mono-methanesulfonyl derivatives VI - IX, or using comparison with authentic samples. Methanolic solutions of hepta-O-acetylsucroses I and II, a mixture of hepta-O-acetylsucroses XI and XII, and octa-O-acetylsucrose were deacetylated on aluminum oxide impregnated by potassium carbonate ant the time dependence of the reaction mixture composition was studied by liquid chromatography. Kinetic measurements show that deacetylation is first order reaction with respect to the starting compounds. With octa-O-acetylsucrose, the most reactive group is that at position 4', so that formation of 1',2,3,3',4,6,6'-hepta-O-acetylsucrose (II) is preferred. Both this compound and 1',2,3,4,4',6,6'-hepta-O-acetylsucrose (XII) are deacetylated to 1',2,3,4,6,6'-hexa-O-acetylsucrose (V). From 2,3,3',4,4',6,6'-hepta-O-acetylsucrose (XI), the 2,3,4,4',6,6'-hexa-O-acetylsucrose (IV) results. Other hexa-O-acetylsucroses, formed by deacetylation of hepta-O-acetylsucroses I and II, are deacetylated to penta-O-acetylsucroses faster than the hexa-O-acetylsucrose V and their proportion in the mixture after deacetylation of octa-O-acetylsucrose is very low. No migration of the O-acetyl group from the position 4' to the position 6' or vice versa occurs during the deacetylation.