Comprehensive Separation and Structural Analyses of Polyphenols and Related Compounds from Bracts of Hops (Humulus lupulus L.)

A novel sequential chromatographic technique was applied to the comprehensive separation of polyphenols and related compounds from a hop bract extract. Over 100 types of constituents were effectively isolated from only 25 g of extract in high yields by high-speed countercurrent chromatography followed by hydrophilic interaction chromatography and reversed-phase high performance liquid chromatography. Among the materials isolated, the structures of 39 compounds were elucidated on the basis of their spectroscopic data including electrospray ionization time-of-flight mass spectrometry and one-dimensional/ two-dimensional nuclear magnetic resonance. Three new compounds, 1 known compound identified for the first time in plants, and 20 known compounds that have not been reported in hops, were found. The hop bract extract also contained an abundance of highly oligomeric proanthocyanidins, which consisted of B-type procyanidin structures.