Synthesis of phenolic acid conjugated chitooligosaccharides and evaluation of their antioxidant activity

In this study, eight kinds of phenolic acid conjugated chitooligosaccharides (PA-c-COSs) with different substitution groups, including p-hydroxyl {hydroxybenzoic acid-c-COS (HBA-c-COS), p-coumaric acid-c-COS (PCA-c-COS)}, 3,4-dihydroxyl {protocatechuic acid-c-COS (PTA-c-COS), caffeic acid-c-COS (CFA-c-COS)}, 3-methoxyl-4-hydroxyl {vanillic acid-c-COS (VNA-c-COS), ferulic acid-c-COS (FRA-c-COS)} and 3,5-dimethoxyl-4-hydroxy {syringic acid-c-COS (SRA-c-COS), sinapinic acid-c-COS (SNA-c-COS)}, were prepared by amide coupling reaction. Their antioxidant properties were evaluated using several in vitro models such as 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl (OH) and nitric oxide (NO) radicals scavenging and reducing power assays. The structures of the synthesized compounds were confirmed by UV, FT-IR and (1)H NMR data. CFA-c-COS showed 81.6% and 89.8% scavenging against DPPH and NO radical formation, respectively. CFA-c-COS also showed higher reducing power and hydroxyl radical scavenging activity compared to those of other compounds. Hence, CFA-c-COS can be a potential antioxidant compound.