Synthesis of hydroxycinnamoyl β-D-xylopyranosides and evaluation of their antioxidant properties

Various hydroxycinnamoyl β-d-xylopyranosides were efficiently prepared from 2,3,4-tri-O-acetyl-α-d-xylopyranosyl bromide (TAXB) with amine by amine-promoted glycosylation. The resulted acetylated hydroxycinnamoyl β-d-xylopyranosides with acetoxy groups at C-2, C-3, and C-4 were regioselectively deacetylated at C-4 position with Novozym 435. Antioxidant activities of free hydroxycinnamic acids and the respective β-d-xylopyranosides were evaluated by DPPHradical dot radical scavenging activity as well as their inhibitory effect on autoxidation of bulk methyl linoleate. The radical scavenging activity on 1,1-diphenyl-2-picrylhydrazyl (DPPHradical dot) decreased in the order ferulic acid > caffeic acid ≈ caffeoyl β-d-xylopyranosides ≈ sinapinic acid > sinapoyl β-d-xylopyranosides ≈ feruloyl β-d-xylopyranosides > p-coumaric acid > p-coumaroyl β-d-xylopyranosides. In bulk methyl linoleate, the antioxidant activity order against autoxidation was almost consistent with the scavenging activity order. The results showed that caffeoyl β-d-xylopyranosides and sinapoyl β-d-xylopyranosides were as effective as free caffeic acid, sinapinic acid, and ferulic acid