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-cinnamoyl glucopyranosyl) 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.
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