Homoserine

Homoserine (also called isothreonine) is an α-amino acid with the chemical formula HO₂CCH(NH₂)CH₂CH₂OH. -Homoserine is not one of the common amino acids encoded by DNA. It differs from the proteinogenic amino acid serine by insertion of an additional -CH₂- unit into the backbone. Homoserine, or its lactone form, is the product of a cyanogen bromide cleavage of a peptide by degradation of methionine.

Homoserine is an intermediate in the biosynthesis of three essential amino acids: methionine, threonine (an isomer of homoserine), and isoleucine. It forms by two reductions of aspartic acid via the intermediacy of aspartate semialdehyde.