Synthesis of L-tryptophan labeled with hydrogen isotopes in the indole ring

The isotopomers of L-tryptophan (L-Trp) labeled with hydrogen isotopes in the indole ring were obtained by isotope exchange method. Heavy and tritiated water were used as the sources of stable and radioactive label. Three isotopomers, i.e., 4′-²H]-L-Trp, 4′-³H]-L-Trp, and doubly labeled 4′-²H/³H]-L-Trp were synthesized by isotope exchange enhanced by irradiation with a mercury discharge lamp. The indole whole ring labeled isotopomers, i.e., 2′,4′,5′,6′,7′-²H₅]-L-, 2′,4′,5′,6′,7′-³H₅]-L-, and doubly labeled 2′,4′,5′,6′,7′-²H/³H]-L-Trp were synthesized by isotope exchange between L-Trp and D₂O or DTO in the presence of deuteriated trifluoroacetic acid.