188751-56-6

The introduction of Nα-9-fluorenylmethyloxycarbonyl (Fmoc) and benzyloxycarbonyl (Z) groups into α,α-dialkylamino acids is described at neutral pH using Fmoc-Cl or Z-Cl as an acylating agent respectively in the presence of activated zing powder. The reaction is simple, fast and clean. It also permits the scale up with high yields. It is completely free from protected oligomer formation, which is a known side-reaction when Schotten-Baumann procedure is followed. All the Fmoc- and Z-amino acids prepared have been fully characterized.

Four previously reported kinin receptor peptide antagonists, including the B1 receptor-selective peptides desArg10-HOE 140 (H-D-Arg-Arg-Pro-Hyp- Gly-Thi-Ser-D-Tic-Oic-OH) and B-9858 (H-Lys-Lys-Arg-Pro-Hyp-Gly-Igl-Ser-D- Igl-Oic-OH), have been modified by replacement of the central tetrapeptide Pro-Hyp-Gly-Xaa with linear alkyl spacers of variable length. The analogue of desArg10-HOE 140 containing the 11-aminoundecanoic acid as spacer, MEN 11575 [H-D-Arg-Arg-NH-(CH2)10-CO-Ser-D-Tic-Oic-OH], was found to be slightly more potent than the unmodified peptide (pA2 = 7.1) as a kinin B1 receptor antagonist in the rat ileum longitudinal smooth muscle assay. Moreover, MEN 11575 is devoid of residual agonist activity at the kinin B1 receptor (rat ileum) and antagonist activity at the kinin B2 receptor (guinea pig ileum longitudinal smooth muscle). Both these activities are displayed by the parent peptide desArg10-HOE 140. Therefore, despite its greatly simplified chemical structure, MEN 11575 shows an improved pharmacological profile in terms of both potency and selectivity, and it represents a good template for the development of new peptidomimetic kinin B1 receptor antagonists. We also report an attempt to investigate the conformational role of the flexible, linear spacer of MEN 11575 and to design more constrained analogues, possibly locked in the bioactive conformation, using semirigid spacers based on C(α)-tetrasubstituted α-amino acids of the family of 1-aminocycloalkane-1-carboxylic acids (Ac(n)c).