(2S,3R)-2-[[(2S,3R)-2-amino-3-hydroxybutanoyl]amino]-3-hydroxybutanoic acid
(2S,3R)-2-[[(2S,3R)-2-amino-3-hydroxy-butanoyl]amino]-3-hydroxy-butanoic acid
(2S,3R)-2-[[(2S,3R)-2-amino-3-hydroxy-1-oxobutyl]amino]-3-hydroxybutanoic acid
(2S,3R)-2-[[(2S,3R)-2-amino-3-hydroxy-butanoyl]amino]-3-hydroxy-butyric acid