Bioassay‐guided isolation of an active compound with protein tyrosine phosphatase 1B inhibitory activity from Sargassum fusiforme by high‐speed counter‐current chromatography

A rapid and efficient method using high‐speed counter‐current chromatography was established for the bioassay‐guided separation of an active compound with protein tyrosine phosphatase 1B inhibitory activity from Sargassum fusiforme. Under the bioassay guidance, the ethyl acetate extract with the best IC₅₀ value of 0.37 ± 0.07 μg/mL exhibited a potential protein tyrosine phosphatase 1B inhibitory activity, which was further separated by high‐speed counter‐current chromatography. The separation was performed with a two‐phase solvent system composed of n‐hexane/methanol/water (5:4:1, v/v). As a result, dibutyl phthalate (19.7 mg) with the purity of 95.3% was obtained from 200 mg of the ethyl acetate extract. Its IC₅₀ was 14.05 ± 0.06 μM, which was further explained by molecular docking. The result of molecular docking showed that dibutyl phthalate enfolded in the catalytic site of protein tyrosine phosphatase 1B. The main force between dibutyl phthalate and protein tyrosine phosphatase 1B was the hydrogen bond interaction with Gln266. In addition, hydrogen bond, van der Waals force and hydrophobic interaction with the amino acids (Ala217, Ile219, and Gly220) were also responsible for the stable protein‐ligand complex.