Tritiated peptides. Part 11. Synthesis of [4-3H-Phe6]-, [4-3H-Phe11]-, and [4-3H-Phe6,11]-somatostatin and the metabolite [des-Ala1]-somatostatin

Abstract

The syntheses are described of somatostatin⁺ labelled with tritium singly in the phenylalanine residues at positions 6 and 11 and doubly at residues 6 and 11 to specific radioactivities of 15.5, 13.8 and 14.1 Cim mol^–1, respectively, by reductive deiodination of fully-protected precursors. Cysteine residues were protected by ^S-trityl groups and the disulphide bridge was formed by iodine oxidation of the tritiated protected precursors. The purity of the products was assessed by acidic hydrolysis, ion-exchange and high-pressure liquid chromatography, and by enzymic digestion of the products modified by reduction and aminoethylation. The synthesis of the metabolite [des-Ala¹]-somatostatin is described. The syntheses of [Phe(I)⁶]-, [Phe(I)¹¹]- and [Phe(I)^6,11]-somatostatin are described.