[Cyclic analogs of des-Arg9-[Leu8]bradykinin].

Four cyclic derivatives of des-Arg9[Leu8]bradykinin have been obtained by classical methods of peptide chemistry. They are cyclo-(-X-Arg-Pro-Pro-Gly-Phe-Gly-Pro-Leu-), where X=Lys or none, and cyclo-(Y-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Leu-), where Y= Lys or Orn. Peptide bonds have been formed by the pentafluorophenylester method, and cyclization has been carried out in a diluted dioxane solution with 40% yield. Subsequent cleavage of protecting groups was made by treatment with hydrogen fluoride. The products obtained were purified by droplet counter-current chromatography. These substances liberate histamine from the rat mast cells comparably to bradykinin and fail to produce myotripic and vascular effects.