Hydroxyl groups introducing NMR strategy for structural elucidation of a heptasaccharide isolated from Trillium...

A heptasaccharide was isolated from an active fraction of Trillium tschonoskii using HILIC and high-temperature PGC chromatography methods. UHPLC-Q/TOF-MS analysis gave this oligosaccharide a degree of polymerization (DP) of 7 and MS/MS showed that it has a six-carbon aldehyde glucan structure with the possible chain 1 → 4 connected. The structure was determined by series 1D and 2D NMR in two solvents D₂O and DMSO‑d₆. Using ¹H resonances of the -OH groups as the starting point and HSQC-TOCSY on the covalent structure definition for structural elucidation allowed this heptasaccharide to be uncovered. This heptasaccharide was elucidated as maltoheptaose via complete assignment of ¹H and ¹³C with jigsaw H-C-OH pieces produced by HSQC-TOCSY at increasing mixing time. The significance of identifying maltoheptaose in Trillium tschonoskii indicates the high potential of -OH introducing strategy for other oligosaccharides' structural determination with relatively higher DP.