Synthesis, characterization, crystal structure, and antioxidant activity of hexahydro-β-acids

Beta-acids are an important component of hops soft resins and usually isolated as by-products during hop processing. Beta-acids have strong antibacterial activity but poor stability. However, hexahydro-β-acids (HBA) are a hydrogenated derivative of β-acids with better stability. In this study, the HBA were successful synthesized by using β-acids as reactant. Its composition was identified by melting point and HPLC and the structure was confirmed by IR, UV, and GC-MS. Similar to β-acids, HBA are composed of hexahydrolupulone, hexahydrocolupulone and hexahydroadlupulone. The crystals of hexahydrocolupulone were separated and characterized by 1H-NMR and single-crystal X-ray diffraction. The crystal structure was determined by direct methods and refined by full-matrix least-squares techniques. The hexahydrocolupulone belongs to orthorhombic system with space group P2(1)2(1)2. Furthermore, the antioxidant activity of HBA were evaluated via DPPH and ORAC assay. The DPPH of EC50 and ORAC value were 0.1334 ± 0.0067 mg/mL and 1308.97 ± 154.02 μmol Trolox/g, respectively.