Nucleophilic Displacement

Abstract

To a solution of ammonium rhodanide (0.16 g, 2 mmol) and 2-methyl-indole [4] (0.26 g, 2.1 mmol) in methanol (6 ml) and acetic acid (18 ml) Nps-Lys(Boc)-Leu-Phe-Lys(Boc)-Lys(Boc)OH (1.12 g, 1.0 mmol) is added and the reaction mixture is allowed to stand at room temperature for 3 hours. The solvent is removed under reduced pressure, the residue washed with warm (about 50 °C) distilled water (twice, 10 ml each time), with 2 N ammonium hydroxide (twice, 10 ml each time), triturated with ether and transferred to a filter. Trituration and washing with ether are continued until a white product is obtained. The partially deprotected pentapeptide is dried in vacuo over P₂O₅ and KOH pellets. It weighs 0.87 g (90%) and melts, with decomposition, at 217 °C; [α] ²⁰_D −4.2° (c 1.2, acetic acid). On elemental analysis satisfactory values are obtained for C, H and N.