Syntheses of metabolites of S-carboxymethyl-L-cysteine and S-methyl-L-cysteine and of some isotopically labelled (2H, 13C) analogues.

The chemical syntheses of human metabolites of S-carboxymethyl-L-cysteine (3) and S-methyl-L-cysteine (12) are described. The additional preparation of some 2H- and 13C-labelled isotopomers enabled the direct evaluation of the stabilities of 3 and 12 under physiological conditions and also facilitated the unambiguous assignments of the signals in the 13C-NMR spectra of all compounds mentioned.