HCV-NS3/4A Protease Inhibitory Iridoid Glucosides and Dimeric Foliamenthoic Acid Derivatives from Anarrhinum orientale

Four new compounds were isolated from the methanol extract of the aerial parts of Anarrhinum orientale: 6′-O-cinnamoylmussaenosidic acid (1), 6′-O-cinnamoyl-8-O-(6′′′-O-cinnamoylglucopyranosyl)mussaenosidic acid (2), (2E,6E)-8-{[(2E,6E)-8-hydroxy-2,6-dimethylocta-2,6-dienoyl]oxy}-2,6-dimethylocta-2,6-dienoic acid (3), and (2E,6E)-8-{[(2E,6E)-8-acetoxy-2,6-dimethylocta-2,6-dienoyl]oxy}-2,6-dimethylocta-2,6-dienoic acid (4). The known 8-O-cinnamoylmussaenosidic acid (5) was also identified. All five compounds were tested for inhibition of the hepatitis C virus (HCV) protease. Compounds 1 and 5 exhibited moderate activity, while 2 and 3 showed weak effects. No inhibitory activity on the human serine protease was observed for any of these compounds, which may infer the selectivity toward the viral protease. A computational docking study of the isolated compounds against HCV protease was used to formulate a hypothetical mechanism for the inhibitory activity of the active compounds on the enzymes tested.