N-Tritioacetoxyphthalimide: A New High Specific Activity Tritioacetylating Reagent

摘要

We have demonstrated the synthesis and use of N-(tritioacetoxy)phthalimide at high specific activity (up to 680 GBq/mmol) as a new and selective reagent for the facile tritium labeling of peptides and other molecules containing a free amino group. The reagent is solid and nonvolatile, and normally 1—1.5 equiv affords rapid and complete acetylation. The chemical and radiochemical stability of this reagent was not specifically studied. However, in one case the tritiated reagent was prepared and stored in acetonitrile, and portions were used for labeling reactions over more than 3 weeks, without any apparent loss of specific activity between reagent and acetylated product. Its facile preparation and analysis make N-(tritioacetoxy)phthalimide synthetically very attractive and superior to either tritiated acetic anhydride or tritiated acetic acid as a tritioacetylating reagent. In comparison with N-succinimidyl [2,3-~3H]propionate, N-(tritioacetoxy)phthalimide is unlikely to affect biological activity, gives rapid acylation, and shows high selectivity between thiol and amino groups. We have also developed a simple and mild method of tritioacetylation of amino acids and peptides in organic solvents (dimethyl sulfoxide, methanol, dioxane) or water. We are currently investigating the utility and selectivity of N-(tritioacetoxy)phthalimide in the high specific activity tritioacetylation of several biologically important compounds containing thiol and hydroxyl functional groups. Similar precursor and labeling chemistry would yield the N-(tritioacetoxy) derivatives of succinimide and naphthalimide. If fully developed into tritioacetylation reagents, these offer the promise of a very useful range of solubility and acetylation characteristics. The hazards associated with the generation and use of highly tritiated acetylation or tin-derived reagents should be carefully assessed in planning experiments such as those described in this work.