An unambiguous structural elucidation of a 1,3-β-d-glucan obtained from liquid-cultured Grifola frondosa by solution NMR experiments

Grifolan LE (GRN-LE), a purified β-d-glucan, which is obtained from liquid-cultured Grifola frondosa, exhibits various biological activities, including antitumor effects. Significant progress has been made in the study of these effects. However, an unambiguous structural characterization of GRN-LE using NMR spectroscopy has not been carried out as yet. It is well accepted that the biological effects of a β-glucan depend on its primary structure, conformation, and molecular weight. In the present study, we unambiguously elucidate the primary structure of GRN-LE using NMR spectroscopy. The data presented here reveal that GRN-LE comprises a 1,3-β-d-glucan backbone with a single 1,6-β-d-glucosyl side branching unit on every third residue.