Alloisoleucine

Alloisoleucine is an amino acid with the formula CH3CH2CH(CH3)CH(NH2)CO2H. It exists as two enantiomers, of which the L derivative occurs naturally. L-Alloisoleucine occurs in healthy serum in only trace amounts, except for individuals suffering from maple syrup urine disease.

Structure
Together with valine, leucine, and isoleucine, alloisoleucine is classified as a branched-chain amino acid (BCAA). It is the rarest of the four.

L-Alloisoleucine is a diastereomer of the proteogenic amino acid L-isoleucine. The stereochemistry of the isobutyl group differs for L-alloisoleucine and L-isoleucine.

Role in biosynthesis
L -allo-isoleucine is a precursor to coronamic acid, which is a constituent of the phytotoxin coronatine, produced by Pseudomonas syringae.