Synthesis of glycosyl ferulate derivatives by amine-promoted glycosylation with regioselective hydrolysis using Novozym 435 and evaluation of their antioxidant properties.

Various glycosyl ferulates were efficiently synthesized from 2,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide (TAGB) with amine by amine-promoted glycosylation without using heavy metal. The resulted acetylated glycosyl ferulates with acetoxyl groups at C-2, C-3 and C-4 were regioselectively deacetylated at C-4 and C-6 positions with Novozym 435. Antioxidant abilities of free ferulic acids and its synthetic glycosyl ferulates were evaluated by inhibitory effect on autoxidation of bulk methyl linoleate as well as their radical scavenging activity. The radical scavenging activity on 1,1-diphenyl-2-picrylhydrazyl (DPPH·) decreased in the order ferulic acid>sinapinic acid ≈ glycosyl sinapinates ≈ glycosyl ferulates>p-coumaric acid>glycosyl p-coumarates. In bulk methyl linoleate, the antioxidant activity order against autoxidation was very consistent with the scavenging activity order. The results showed that glycosyl ferulates and sinapinates were effective as well as free carboxylic acid forms.