Structures of hexa-O-acetylsucroses formed by deacetylation of sucrose octa-O-acetate

Abstract

A fraction corresponding to hexa-O-acetylsucrose was isolated in 34% yield from the reaction mixture after deacetylation of sucrose octa-acetate by aluminium oxide impregnated by potassium carbonate. Its subsequent reaction with p-toluenesulfonyl chloride in pyridine provided crystalline 1',2,3,4,6,6'-hexa-O-acetyl-3',4'-di-O-p-toluenesulfonylsucrose (III). With triphenylphosphine-diethyl azodicarboxylate reagent, 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl 1,6-di-O-acetyl-3,4-anhydro-β-D-lyxo-hexulofuranoside (VI) was obtained. Treatment of ditosyl derivative III with sodium methoxide followed by acetylation gave besides the anhydro derivative VI also the anhydro derivative V with ribo configuration. The same reaction carried out with mother liquors after crystallization of ditosyl derivative III yielded in addition to anhydro derivatives V and VI the crystalline 1',2-anhydro(3,4,6-tri-O-acetyl-α-D-glucopyranosyl 6'-O-acetyl-3',4'-anhydro-β-D-ribo-hexulofuranoside) (VII). From these results and the analysis of NMR and mass spectra of the hexa-O-acetylsucrose, it follows that the deacetylation of sucrose octa-acetate is highly regioselective, providing the mixture of 1',2,3,4,6,6'-hexa-O-acetylsucrose (I) and 2,3,4,4',6,6'-hexa-O-acetylsucrose (XIII) with markedly prevailing the former component. The structure of dianhydro derivative VII (except the oxirane ring configuration) was determined by NMR spectroscopy. The configuration of this ring follows from the fact that the treatment of 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl 6-O-acetyl-3,4-anhydro-1-O-methanesulfonyl-β-D-lyxo-hexulofuranoside (IX) with sodium methoxide followed by acetylation does not give the dianhydro derivative VII. However, this compound is formed from the anhydro derivative V by its partial deacetylation, mesylation, reaction with sodium methoxide, and acetylation.