The Synthesis of a Heavy-Atom Derivative of Gramicidin S (GS), [ d -Phe(4-Br)4,4′]-GS, by a Novel Method

A new approach for the preparation of cyclic peptides was successfully applied to the synthesis of cyclo(–Val–Orn–Leu–d–Phe(4-Br)–Pro–Val–Orn–Leu–d–Phe (4-Br)–Pro–) ([d–Phe(4-Br)4,4′]-GS). [d–Phe(4-Br)4,4′]–GS showing antibacterial activity was obtained as crystals.