tert-butyl (7S)-7-[[(2S)-1-methoxy-1-oxo-3-[(1S)-2-oxocyclopentyl]propan-2-yl]carbamoyl]-6-azaspiro[3.4]octane-6-carboxylate;4-methoxy-1H-indole-2-carboxylic acid;methyl (2S)-2-aminochloranuidyl-3-[(1S)-2-oxocyclopentyl]propanoate;methyl (2S)-2-[[(7S)-6-azaspiro[3.4]octane-7-carbonyl]amino]-3-[(1S)-2-oxocyclopentyl]propanoate;methyl (2S)-2-[[(7S)-6-(4-methoxy-1H-indole-2-carbonyl)-6-azaspiro[3.4]octane-7-carbonyl]amino]-3-[(1S)-2-oxocyclopentyl]propanoate;methyl (2S)-2-methyl-3-[(1S)-2-oxocyclopentyl]propanoate;(7S)-6-[(2-methylpropan-2-yl)oxycarbonyl]-6-azaspiro[3.4]octane-7-carboxylic acid