Synthesis and structure-bioactivity relationship of sugar-esters

Abstract

This research involved the synthesis of sugar esters and structure-antioxidant relationship study. Twenty-eight sugar esters as glycoconjugate were manipulated through esterification using DMAP and DCC. The derived products were well-characterized by various spectroscopic methods. Fourteen compounds (1C, 2C, 3C, 4C, 5C, 8C, 2D, 4D, 6D, 7D, 3E, 5E, 2I and 2J) were identified as new substances. Four parameters were set up to explore the relationship of structure and activity including types of substituents, types of substituents on a benzoic acid ring, effects of hydroxyl group on a benzoic ring and numbers of benzoic acid derivatives on the sugar ester structure. 1,2,3,4,6-Penta-O-(3,4-dihydroxybenzoyl)glucopyranoside (2J) revealed higher antioxidant activity as a radical scavenger againts DPPH radical than BHA but comparable to gallic acid. Sugar esters bearing as benzyl, pivaloyl, acetyl and methoxy groups were inactive. The arrangement of phenolic dihydroxyl groups as ortho to one another substantially increased the antioxidant activity for the parent sugar esters. For instance, monosubstituted 3,4-dihydroxybenzoic acid sugar ester (3D) expressed higher activity than 3,5-dihydroxybenzoic acid (4D) and 2,4-dihydroxybenzoic acid (2D) sugar esters. This could be stemmed from the resonance effect and H-bonding of hydroxyl groups at the ortho position