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

Abstract 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 DPPH 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 (DPPH ) 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.