Our group has developed a stereospecific enzymatic method, which is very efficient for the in vitro synthesis of l-[(15)N]serine, l-[(15)N]methionine and l-[(15)N]glutamic acid. These amino acids were prepared from the corresponding alpha -ketoacids in the suitable enzymatic systems. The bacterial NAD-dependent amino acid dehydrogenases alanin dehydrogenase, leucin dehydrogenase and glutamate dehydrogenase were used as catalysts. Glucose dehydrogenase was used for the regeneration of NADH and (15)NH(4)Cl as isotopically labelled material at 99 at.% (15)N. All reactions are inexpensive and easy to perform on a synthetically useful scale (1-10g) giving high yields of l-amino acids. The (15)N isotope content was determined by mass spectrometry.
