(2R)-2-[[(2S)-2-aminopropanoyl]amino]-5-hydroxy-5-oxopentanoate
(2R)-2-[[(2S)-2-aminopropanoyl]amino]-5-hydroxy-5-oxo-pentanoate
(2R)-2-[[(2S)-2-amino-1-oxopropyl]amino]-5-hydroxy-5-oxopentanoate
(2R)-2-(alanylamino)-5-hydroxy-5-keto-valerate