a-b-dihydroxy-b-methylvalerate
(R)-2,3-dihydroxy-3-methylpentanoate
(R)-2,3-dihydroxy-3-methylvalerate

C6H12O4

It's an a-keto acid (molecule formed after the deamination of an amino acid - in this case isoleucine) precursor. In order to form the valine carbon skeleton, it has to be dehydrated twice (to remove the C2 and C3 hydroxyls).

Synthesis of alanine, leucine, valine and isoleucine (3D)