In vitro and in vivo activity of analogues of the kinin B2 receptor antagonist MEN1 1270

In this study, we describe the in vitro and in vivo activities of a series of cyclic peptide analogues of the selective kinin B2 receptor antagonist MEN11270 on Chinese hamster ovary cells expressing the human B2 receptor (hB2R), the human isolated umbilical vein (hUV), the isolated guinea pig ileum (gpI), and bradykinin (BK) induced bronchoconstriction (BC) and hypotension in anaesthetized guinea pigs. Substitutions in the backbone of MEN1 1270 (H-DArg-Arg-Pro-Hyp-Gly-Thi-c(Dab-DTic-Oic-Arg)c(7gamma-10alpha)) aimed to increase the potency in inhibiting bronchospasm versus hypotension following the topical (intratracheal (i.t.)) or systemic (intravenous (i.v.)) application of these antagonists. A series of analogues were left unprotected from N-terminal cleavage by aminopeptidases (MEN12739, MEN13052, MEN13346, and MEN13371): these compounds maintained sizeable affinities for the hB2R (pKi = 9.4, 9.6, 9.7, and 8.6, respectively) and antagonist activities toward BK in the hUV (pA2 = 7.9, 8.3, 8.2, and 7.5) and gpI assays (pK(B) = 7.4, 7.8, 7.9, and 7.9), but the inhibition of BK-induced BC and hypotension in vivo was negligible following either i.v. or i.t. administration. Two analogues (MEN12388 and MEN13405) could be potential substrates of angiotensin-converting enzyme: these have good activity in the hB2R (pKi = 9.5 and 8.9, respectively), hUV (pA2 = 8.2 for MEN12388), and gpI assays (pK(B) = 8.4 and 8.0) but an in vivo activity 10- to 30-fold lower than the parent compound MEN1 1270 (pKi = 9.4, pA2 = 8.1, pKB = 8.3) when given by either the i.v. or the i.t. route. Other analogues were functionalized with a quaternary ammonium Lys derivative (MEN13031, MEN12374, and the previously mentioned MEN13052) or with an ethyl group on Arg (MEN13655 and the previously mentioned MEN13346 and MEN13405) in order to hinder or facilitate local absorption. MEN13346 and MEN13031 (pKi = 9.7and 9.5, pA2 = 8.2 and 7.9, pKB = 7.9 and 8.5, respectively) were 10- to 30-fold less active in vivo than MEN1 1270, without improving the discrimination between BK-induced BC and hypotension after either systemic or topical administration. It is concluded that the decreased in vivo activities of cyclic analogues of MEN11270 on BK-induced BC and hypotension following either their intratracheal or their intravenous routes of administration might be due in large part to metabolic degradation.

Solid-phase synthesis of MEN 11270, a new cyclic peptide kinin B2 receptor antagonist

An efficient synthesis of the cyclic decapeptide MEN 11270 [H-DArg1-Arg2 Pro3-Hyp4-Gly5-Thi6-Dab7-DTic8-Oic9-Arg10 c(7gamma - 10alpha)] was developed. Two three-dimensional orthogonal strategies were applied and compared: Fmoc/Tos/Boc (procedure A) and Fmoc/Pmc/Dde (procedure B). Both resulted in a 23-step strategy comprising the stepwise solid-phase chain assembly of the linear protected peptide, partial deprotection, solution-phase cyclization and final full deprotection. The stepwise assembly of the linear peptide was optimized by double coupling and acylation time prolongation for critical residues (Tic, Dab, Thi, Pro). O-(7-azabenzotriazol-1-yl)-N,N,N',N' tetramethyluronium (HATU) was preferred as coupling reagent for Dab. In the cyclization step, the partial racemization of Arg10 (31% using 1-ethyl-3-(3'-dimethyl-aminopropyl) carbodiimide/1-hydroxybenzotriazole (EDC/HOBt) as activation system) was reduced to 3% with HATU. The final deprotection was performed in the presence of dimethylsulfide (procedure A) and thiocresol (procedure B) as scavengers, to avoid the sulfation of Hyp side chain. The final compound and the main by-products were characterized by mass spectroscopy (MS), nuclear magnetic resonance (NMR) and racemization test. Procedure B produced operationally simpler and more efficient results than A (28% overall yield versus 4%).