(S)-2-(n-butoxycarbonylamino)-5-[2-(4-carbamimidoylphenyl)-1-oxo-2,8-diazaspiro[4.5]dec-8-yl]-5-oxopentanoic acid ethyl ester

(S)-2-(n-butoxycarbonylamino)-5-[2-(4-cyanophenyl)-1-oxo-2,8-diazaspiro[4.5]dec-8-yl]-5-oxopentanoic acid ethyl ester

ethyl (S,Z)-2-((butoxycarbonyl)amino)-5-(2-(4-(N'-hydroxycarbamimidoyl)phenyl)-1-oxo-2,8-diazaspiro[4.5]decan-8-yl)-5-oxopentanoate

(4S)-4-{[(4-methylphenyl)sulfonyl]amino}-5-ethoxy-5-oxopentanoic acid

(4S)-4-[(butylsulfonyl)amino]-5-ethoxy-5-oxopentanoic acid