Cycloleucine is a non-proteinogenic amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

. It could be classified as a cyclic derivate of norleucine

Norleucine

Norleucine is an isomer of leucine, the α-amino acid 2-amino-hexanoic acid. It is not found in natural proteins. Norleucine is used in experimental studies of protein structure and function....

, having two hydrogen atoms less. Leading structure is a cyclopentane

Cyclopentane

Cyclopentane is a highly flammable alicyclic hydrocarbon with chemical formula 510 and CAS number 287-92-3, consisting of a ring of five carbon atoms each bonded with two hydrogen atoms above and below the plane. It occurs as a colorless liquid with a petrol-like odor. Its melting point is −94 °C...

-ring. The α-carbon atom is not a stereocenter.

Cycloleucine is a non-metabolisable amino acid and is a specific and reversible inhibitor

Enzyme inhibitor

An enzyme inhibitor is a molecule that binds to enzymes and decreases their activity. Since blocking an enzyme's activity can kill a pathogen or correct a metabolic imbalance, many drugs are enzyme inhibitors. They are also used as herbicides and pesticides...

 of nucleic acid methylation, and as such is widely used in biochemical experiments..