alpha-Aminobutyric acid

α-Aminobutyric acid (AABA), also known as homoalanine in biochemistry, is a non-proteinogenic alpha amino acid with chemical formula C₄H₉NO₂. The straight two carbon side chain is one carbon longer than alanine, hence the prefix homo-.

Homoalaine is biosynthesised by transaminating oxobutyrate, a metabolite in isoleucine biosynthesis. It is used by nonribosomal peptide synthases. One example of a nonribosomal peptide containing homoalanine is ophthalmic acid, which was first isolated from calf lens.