Specific tritiation of indole derivatives by catalytic desulfenylation. Application to the labelling of tryptophan-containing peptides

A new method for tritiating indole derivatives was studied. The procedure consisted first of the formation of an o-nitrophenylsulfenyl tryptophanyl derivative by reacting the compound with o-nitrophenylsulfenyl chloride; then the sulfenylated product was submitted to catalytic hydrogenolysis in the presence of tritium gas. This latter reaction led to the desulfenylation of the compound and permitted the replacement of the thioether function by a tritium atom. By this procedure l-tryptophan, N-acetyl-l-tryptophanamide and a gastin-like pentapeptide derivative, Boc-Gly-Trp-Met-Asp-Phe(NH2), have been tritiated; 15, 16 and 7 Ci/mmol have been obtained respectively. The labelled compounds have retained the properties of the native materials.