2-Hydroxybutyric acid (or alpha-hydroxybutyrate) is a hydroxybutyric acid with the hydroxyl group on the carbon adjacent to the carboxyl. It is a chiral compound having two enantiomers, -2-hydroxybutyric acid and -2-hydroxybutyric acid.
2-Hydroxybutyrate, the conjugate base of 2-hydroxybutyric acid, is produced in mammalian tissues (principally hepatic) that catabolize -threonine or synthesize glutathione. Oxidative stress or detoxification demands can dramatically increase the rate of hepatic glutathione synthesis. Under such metabolic stress conditions, supplies of -cysteine for glutathione synthesis become limiting, so homocysteine is diverted from the transmethylation pathway forming methionine into the transsulfuration pathway forming cystathionine. 2-Hydroxybutyrate is released as a byproduct when cystathionine is cleaved to cysteine that is incorporated into glutathione. Chronic shifts in the rate of glutathione synthesis may be reflected by urinary excretion of 2-hydroxybutyrate.