Cyclic analogues of Thr⁶‐bradykinin, N⁸‐Lys‐bradykinin and endo‐Lys^8a‐vespulakinin 1

Abstract

Syntheses are described of the endo‐Lys8a‐vespulakinin 1 and of cyclo‐Thr6‐ and cyclo‐Nε‐Lys‐bradykinin. The linear peptides covering the entire sequences of endo‐Lys8a‐VSK‐1 and Thr6‐BK, and the decapeptide containing all residues constituting Lys‐BK, with a Arg‐Lys peptide bond involving the ε‐amino function of lysine, were prepared by the solid‐phase procedure based on Fmoc chemistry. Cyclization was carried out by the diphenylphosphorazide method. The amino‐terminal octapeptide sequence of vespulakinin 1, Fmoc‐Thr(tBu)‐Ala‐Thr(tBu)‐Thr(tBu)‐Arg(Pmc)‐Arg(Pmc)‐Arg(Pmc)‐Gly‐OH, and its Nα‐Boc‐[(Gal β)Thr3, (Gal β)Thr4]‐analogue, were used to prepare Nα‐(1–8 VSK 1)‐cyclo‐Nε‐kallidin and Nα‐[(Gal β)Thr3, (Gal β)Thr4, 1–8 VSK 1]‐cyclo‐Nε‐kallidin. Peptides and glycopeptides were characterized by amino‐acid analysis, optical rotation, analytical HPLC and FAB‐MS. Consistent with previous findings, preliminary pharmacological experiments on smooth muscle preparations showed that the cyclic, or partially cyclic, analogues were significatively less potent than the linear ones. © Munksgaard 1995.