Structure elucidation of fucoidan composed of a novel tetrafucose repeating unit from sea cucumber Thelenota ananas

Thelenota ananas is one of the most popular edible sea cucumber species consumed in China and some Southeast Asian countries. In this study, the delicate structure of fucoidan from T. ananas (Ta-FUC) was clarified. Oligosaccharides and low molecular weight polysaccharides of Ta-FUC were prepared by enzymatic degradation. Their structures, which retained primary structural features of Ta-FUC, were investigated using tandem mass spectrometry and nuclear magnetic resonance. As a result, Ta-FUC was found to be composed of a novel tetrafucose repeating unit [→3-α-L-Fucp-1→3-α-L-Fucp-1→3-α-L-Fucp2,4(OSO3-)-1→3-α-L-Fucp2(OSO3-)-1→]. Meanwhile, it was proven to possess a significant inhibitory effect on superoxide radicals with an IC50 of 17.46 ± 0.14 μg/ml. This effect was related to its sulphation pattern.