ORIGINAL PAPER Structure analysis of sulfated polysaccharides extracted from green seaweed Ulva lactuca: experimental and density functional theory studies Thi Thanh Van Tran 1 • Bui The Huy 2,3 • Hai Bang Truong 1 • Minh Ly Bui 1 • Thi Thu Thuy Thanh 4 • Duy Quang Dao 2 Received: 22 June 2017 / Accepted: 4 September 2017 Ó Springer-Verlag GmbH Austria 2017 Abstract The structure of sulfated polysaccharides extracted from green seaweed Ulva lactuca has been determined using NMR experiments. The obtained results indicate that this natural product is mainly composed of disaccharide A 3S : [?4)-b-D-GlcA-(1 ? 4)-a-L-Rha3S- (1?] and B 3S :[?4)-a-L-IdoA-(1 ? 4)-a-L-Rha3S-(1?]. The computational calculations using density functional theory (DFT) at the B3LYP/6–311?G(2d,p)//B3LYP/ 6–311G(d,p) model chemistries were also investigated to analyze the obtained structures based on the comparison of 1 H and 13 C NMR chemical shifts. The DFT results also confirm that the A 3S structure is more dominating than the B 3S one with the mean absolute error of 1 H and 13 C NMR chemical shifts, respectively, equal to 0.46 and 4.98 ppm for the A 3S and to 2.07 and 5.03 ppm for the B 3S . Graphical abstract Keywords Ulva lactuca Á Density functional theory Á Chemical shift Á NMR prediction Á Sulfated polysaccharides Introduction Ulvan is the water-soluble sulfated polysaccharide derived from green seaweed genera Ulva and Enteromorpha. The chemical composition of this polysaccharide is reported to involve rhamnose, xylose, glucuronic acid, iduronic acid, and sulfate groups [1, 2]. In recent years, many researches on ulvan have been conducted for interest in its structure and valuable bioactivity [3–6]. Lahaye et al. [7] reviewed that ulvan complex structures are considered to vary, depending on algae species, places of cultivation and extracting methods. In general, the structures include major repeating sequences ulvanobiouronic 3-sulfate (type A3S or B3S); ulvanobiose 3-sulfate (type U3S or U2 0 S,3S) and many other repeating ones. Specifically in edible species U. lactuca, the published results showed that the structural composition of polysaccharides is complex and variable [3, 8, 9] and it is composed of (1 ? 4)- and (1?2,4)- Rha3S, (1 ? 4)-GlcA, and (1 ? 4)-Xyl2S. The sugar Electronic supplementary material The online version of this article (doi:10.1007/s00706-017-2056-z) contains supplementary material, which is available to authorized users. & Duy Quang Dao daoduyquang@gmail.com 1 Nhatrang Institute of Technology Research and Application, Vietnam Academy of Science and Technology, 02 Hung Vuong, Nha Trang, Viet Nam 2 Institute of Research and Development, Duy Tan University, 03 Quang Trung, Da Nang, Viet Nam 3 Department of Chemistry, Changwon National University, Changwon 51140, Korea 4 Institute of Chemistry, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Ha Noi, Viet Nam 123 Monatsh Chem DOI 10.1007/s00706-017-2056-z