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-.

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α-Aminobutyric acid

Names
IUPAC name Homoalanine
Systematic IUPAC name 2-Aminobutanoic acid
Other names 2-Aminobutyric acid; α-Aminobutanoic acid; Ethylglycine; 2-Azaniumylbutanoate
Identifiers
CAS Number	2835-81-6 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:35621 Y
ChEMBL	ChEMBL55242 Y
ChemSpider	6405 Y
ECHA InfoCard	100.018.742
PubChem CID	6657
UNII	8306QPJ19P Y
CompTox Dashboard (EPA)	DTXSID90862679
InChI InChI=1S/C4H9NO2/c1-2-3(5)4(6)7/h3H,2,5H2,1H3,(H,6,7) Y Key: QWCKQJZIFLGMSD-UHFFFAOYSA-N Y InChI=1/C4H9NO2/c1-2-3(5)4(6)7/h3H,2,5H2,1H3,(H,6,7) Key: QWCKQJZIFLGMSD-UHFFFAOYAG
SMILES O=C(O)C(N)CC
Properties
Chemical formula	C4H9NO2
Molar mass	103.12 g/mol
Appearance	white solid
Melting point	305 °C (581 °F; 578 K)
Acidity (pKa)	2.55 (carboxyl), 9.60 (amino)[1]
Magnetic susceptibility (χ)	-62.1·10−6 cm3/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

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Homoalanine 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.

α-Aminobutyric acid is one of the three isomers of aminobutyric acid. The two other are the neurotransmitter γ-Aminobutyric acid (GABA) and β-Aminobutyric acid (BABA) which is known for inducing plant disease resistance.

The conjugate base of α-aminobutyric acid is the carboxylate α-aminobutyrate.

This amino acid has been detected in meteorites.^[2]