Gunnar Lindeberg

The solution conformation of the antibacterial polypeptide cecropin A from the Cecropia moth is investigated by nuclear magnetic resonance (NMR) spectroscopy under conditions where it adopts a fully ordered structure, as judged by previous circular dichroism studies. By use of a combination of two-dimensional NMR techniques the ¹H NMR spectrum of cecropin A is completely assigned. A set of 243

Recent site directed mutagenesis studies on the melanocortin 1 (MC1) receptor have indicated the importance of D117 and H260 amino acid residues for the binding of alpha-MSH (melanocyte stimulating hormone). Here, we report the testing of 12 cyclic and linear MSH peptides on the D117A and H260A mutant receptors. Moreover, we constructed a double mutant which displayed a major loss in affinity for [Nle4, D-Phe7]alpha-MSH. Our new data of His6 and Phe7 substituted MSH peptides are compared with previous results and the hypothesis of putative interactions of D117 and H260 with single amino acids in the MSH peptide. Our conclusions are that the D117A and the H260A mutations may cause conformational changes in the receptor which can not be linked to any specific amino acid in the MSH-peptides.

The insulin-regulated aminopeptidase (IRAP) localized in areas of the brain associated with memory and learning is emerging as a new promising therapeutic target for the treatment of memory dysfunctions. The angiotensin II metabolite angiotensin IV (Ang IV, Val(1)-Tyr(2)-Ile(3)-His(4)-Pro(5)-Phe(6)) binds with high affinity to IRAP and inhibits this aminopeptidase (K(i) = 62.4 nM). Furthermore, Ang IV has been demonstrated to enhance cognition in animal models and is believed to play an important role in cognitive processes. It is herein reported that displacement of the C-terminal tripeptide His(4)-Pro(5)-Phe(6) with a phenylacetic acid functionality combined with a constrained macrocyclic system in the N-terminal affords potent IRAP inhibitors that are less peptidic in character than the hexapeptide Ang IV. Configurational analysis of three pairs of diastereomeric Ang IV analogues was performed using a combination of solution NMR spectroscopic methods, Monte Carlo conformational searches, and NAMFIS calculations. The compounds encompassing l-amino acids only (4, 8, and 12) showed significantly higher bioactivity compared to their lld-epimers (5, 9, and 13). The best inhibitors in the series, compounds 8 and 12, incorporating a 13- and 14-membered disulfide ring system, respectively, and both with a β(3)-homotyrosine residue (β(3)hTyr) replacing Tyr(2), exhibit K(i) values of 3.3 and 5.2 nM, respectively.

Synthesis and inhibitory potencies of three types of protease inhibitors of the hepatitis C virus (HCV) full-length NS3 (protease-helicase/NTPase) are reported: (i) inhibitors comprising electrophilic serine traps (pentafluoroethyl ketones, alpha-keto acids, and alpha-ketotetrazoles), (ii) product-based inhibitors comprising a C-terminal carboxylate group, and (iii) previously unexplored inhibitors comprising C-terminal carboxylic acid bioisosteres (tetrazoles and acyl sulfonamides). Bioisosteric replacement with the tetrazole group provided inhibitors equally potent to the corresponding carboxylates, and substitution with the phenyl acyl sulfonamide group yielded more potent inhibitors. The hexapeptide inhibitors Suc-Asp-D-Glu-Leu-Ile-Cha-Nva-NHSO(2)Ph and Suc-Asp-D-Glu-Leu-Ile-Cha-ACPC-NHSO(2)Ph with K(i) values of 13.6 and 3.8 nM, respectively, were approximately 20 times more potent than the corresponding inhibitors with a C-terminal carboxylate and were comparable to the carboxylate-based inhibitor containing the native cysteine, Suc-Asp-D-Glu-Leu-Ile-Cha-Cys-OH (K(i)=28 nM). The acyl sulfonamide group constitutes a very promising C-terminal functionality that allows for prime site optimization.

Macrocyclization is a commonly used strategy to preorganize HCV NS3 protease inhibitors in their bioactive conformation. Moreover, macrocyclization generally leads to greater stability and improved pharmacokinetic properties. In HCV NS3 protease inhibitors, it has been shown to be beneficial to include a vinylated phenylglycine in the P2 position in combination with alkenylic P1' substituents. A series of 14-, 15- and 16-membered macrocyclic HCV NS3 protease inhibitors with the linker connecting the P2 phenylglycine and the alkenylic P1' were synthesized by ring-closing metathesis, using both microwave and conventional heating. Besides formation of the expected macrocycles in cis and trans configuration as major products, both ring-contracted and double-bond migrated isomers were obtained, in particular during formation of the smaller rings (14- and 15-membered rings). All inhibitors had K(i)-values in the nanomolar range, but only one inhibitor type was improved by rigidification. The loss in inhibitory effect can be attributed to a disruption of the beneficial π-π interaction between the P2 fragment and H57, which proved to be especially deleterious for the d-phenylglycine epimers.

Phenylglycine has proved to be a useful P2 residue in HCV NS3 protease inhibitors. A novel pi-pi-interaction between the phenylglycine and the catalytic H57 residue of the protease is postulated. We hypothesized that the introduction of a vinyl on the phenylglycine might strengthen this pi-pi-interaction. Thus, herein is presented the synthesis and inhibitory potency of a series of acyclic vinylated phenylglycine-based HCV NS3 protease inhibitors. Surprisingly, inhibitors based on both D- and L-phenylglycine were found to be effective inhibitors, with a slight preference for the d-epimers. Furthermore, prime-side alkenylic extension of the C-terminal acylsulfonamide group gave significantly improved inhibitors with potencies in the nanomolar range (approximately 35 nM), potencies which were retained on mutant variants of the protease.

A pentapeptide, Ala-Arg-Pro-Ala-Lys, liberated from fibrinogen during plasmin-mediated fibrinolysis, was shown earlier to increase microvascular permeability in rat and human skin. Eighteen new analogues have now been synthesized in addition to the 15 previously prepared and examined for their effect on permeability. The old concept that a tetrapeptide with basic amino acids at both ends and a proline residue adjacent to the N-terminal amino acid is essential for high activity on permeability, has now been challenged. The results obtained with several of the new analogues strengthen this concept. More interestingly, however, the third amino acid, which was found in earlier studies to be less sensitive to exchange, has now been deleted as well as duplicated with only a modest loss of activity of the peptide. The chirality of the C-terminal amino acid, most surprisingly, does not seem to be crucial for peptide activity. Slightly superpotent analogues were obtained on amidation of the C-terminus. In addition, a few naturally occurring peptides, namely tuftsin, substance P, neurotensin and bradykinin, the amino acid sequences of which all exhibit characteristic features of some of our active peptide analogues were investigated in the same test system. Tuftsin displayed a potency equal to that of the pentapeptide. The other three peptides were all highly superpotent in this assay system.