Synthesis of 4-thia-[6-(13)C]lysine from [2- (13)C]glycine: access to site-directed isotopomers of 2-aminoethanol, 2-bromoethylamine and 4-thialysine.

4-Thialysine (S-(2-aminoethyl)-L: -cysteine) is an analog of lysine. It has been used as an alternative substrate for lysine in enzymatic reactions. Site-directed isotopomers are often needed for elucidation of mechanism of reactions. 4-Thialysine can be synthesized by reacting cysteine with 2-bromoethylamine, an important reagent in chemical-modification rescue (CMR) of proteins. Here, we present the synthesis of 4-thia-[6-(13)C]lysine, one of the isotopomers of 4-thialysine, from commercially available starting material [2-(13)C]glycine via formation of five intermediates including 2-amino[2-(13)C]ethanol and 2-bromo[1-(13)C]ethylamine. The compounds were characterized using various spectroscopic techniques. Moreover, we discuss that our strategy would provide access to site-directed isotopomers of 2-aminoethanol, 2-bromoethylamine and 4-thialysine. Biological activity of 4-thia-[6-(13)C]lysine was tested in the enzymatic reaction of lysine 5,6-aminomutase.