DL-Homocysteine-d4 is the deuterium labeled DL-Homocysteine. DL-Homocysteine is a weak neurotoxin, and can affect the production of kynurenic acid in the brain[1][2].
Stable heavy isotopes of hydrogen, carbon, and other elements have been incorporated into drug molecules, largely as tracers for quantitation during the drug development process. Deuteration has gained attention because of its potential to affect the pharmacokinetic and metabolic profiles of drugs[1].
[1]. Russak EM, et al. Impact of Deuterium Substitution on the Pharmacokinetics of Pharmaceuticals. Ann Pharmacother. 2019;53(2):211-216.
[2]. DL-Homocysteine, et al. Dual effect of DL-homocysteine and S-adenosylhomocysteine on brain synthesis of the glutamate receptor antagonist, kynurenic acid. J Neurosci Res. 2005 Feb 1;79(3):375-82.