(2R)-2-amino-4-hydroxybutanoic acid (2R)-2-amino-4-hydroxy-butanoic acid (2R)-2-amino-4-hydroxy-butyric acid (R)-()-2-Amino-4-hydroxybutyric acid H4021_SIGMA CHEBI:30654 (2R)-2-azaniumyl-4-hydroxybutanoate (2R)-2-azaniumyl-4-hydroxy-butanoate (2R)-2-ammonio-4-hydroxybutanoate (2R)-2-ammonio-4-hydroxy-butyrate ZINC01742215