L-threonine
2-Amino-3-hydroxybutiric acid

C4H9NO3

It's an amino acid.

Catabolism of methionine, threonine, isoleucine and valine (3D)
Catabolism of threonine, tryptophan, glycine, proline, arginine, cysteine and serine (3D)
Synthesis of aspartate, methionine, lysine and threonine (3D)
Synthesis of aminoacyl t-RNA (Kyoto University)