Disclosed are spiro compounds of formula I or pharmaceutically acceptable salts thereof, and methods for their synthesis. Specific examples of compounds of formula I include: (5S,8S)-7-((S)-2-(2-cyclohexylacetamido)-3,3-dimethylbutanoyl)-N-((S)-1-(cyclopropylamino)-1,2-dioxohexan-3-yl)-2-oxo-3-phenyl-1-oxa-3,7-diazaspiro[4.4]nonane-8-carboxamide, (5R,8S)-7-((S)-2-(2-cyclohexylacetamido)-3,3-dimethylbutanoyl)-N-((S)-1-(cyclopropylamino)-1,2-dioxohexan-3-yl)-2-oxo-3-phenyl-1-oxa-3,7-diazaspiro[4.4]nonane-8-carboxamide, Cyclopentyl-(S)-1-((3S,5R)-3-((S)-1-(cyclopropylamino)-1,2-dioxohexan-3-ylcarbamoyl)-8-oxo-7-phenyl-2,7-diazaspiro[4.4]nonan-2-yl)-3,3-dimethyl-1-oxobutan-2-ylcarbamate, and Cyclopentyl (S)-1-((3S,5S)-3-((S)-1-(cyclopropylamino)-1,2-dioxohexan-3-ylcarbamoyl)-8-oxo-7-phenyl-2,7-diazaspiro[4.4]nonan-2-yl)-3,3-dimethyl-1-oxobutan-2-ylcarbamate. Also disclosed is the use of compounds of formula I for treating a hepatitis C virus (HCV) infection.
