Peptidomimetics as receptors agonists or peptidase inhibitors: a structural approach in the field of enkephalins, ANP and CCK

[Conformational analysis of cyclic dipeptides: I]

Conformational analysis of two pairs of synthetic cyclodipeptides formed by interaction of both side chain functional groups [Formula: see text] and of the main and side chains [Formula: see text] was achieved by the method of molecular mechanics. The energetically optimal conformational states of the molecules under study were determined. It was shown that the conformational motility of cyclic system of the compounds under study depends on the relative arrangement of the amide groups and the number of atoms in the cycle.

Aminopeptidase-N/CD13 (EC 3.4.11.2) inhibitors: chemistry, biological evaluations, and therapeutic prospects

Aminopeptidase N (APN)/CD13 (EC 3.4.11.2) is a transmembrane protease present in a wide variety of human tissues and cell types (endothelial, epithelial, fibroblast, leukocyte). APN/CD13 expression is dysregulated in inflammatory diseases and in cancers (solid and hematologic tumors). APN/CD13 serves as a receptor for coronaviruses. Natural and synthetic inhibitors of APN activity have been characterized. These inhibitors have revealed that APN is able to modulate bioactive peptide responses (pain management, vasopressin release) and to influence immune functions and major biological events (cell proliferation, secretion, invasion, angiogenesis). Therefore, inhibition of APN/CD13 may lead to the development of anti-cancer and anti-inflammatory drugs. This review provides an update on the biological and pharmacological profiles of known natural and synthetic APN inhibitors. Current status on their potential use as therapeutic agents is discussed with regard to toxicity and specificity.

Synthesis and biological properties of new constrained CCK-B antagonists: discrimination of two affinity states of the CCK-B receptor on transfected CHO cells

To improve our knowledge of the bioactive conformation of CCK-B antagonists, we have developed a new series of constrained dipeptoids whose synthesis and biochemical properties are reported here. These compounds, of general structure N alpha-[(2-adamantyloxy)carbonyl]-alpha-methyltryptophanyl-(4 -X)-proline, were designed by introducing a cyclization in the structure of the previously described CCK-B/peptoid antagonist RB 210, N-[N-[(2-adamantyloxy)carbonyl]-DL-alpha-methyltryptophanyl] -N-(2-phenylethyl)glycine (Blommaert et al. J. Med. Chem. 1993, 36, 2868-2877), by means of a five-membered ring. Structure-affinity relationship studies showed that an R configuration of Trp-C alpha and a cis configuration of the pyrrolidine substituents were favorable for receptor recognition. The most potent compounds of this new series had similar affinities for the CCK-B receptor as RB 210 and proved to be far more efficient in inhibiting inositol phosphate production in CHO cells stably transfected with rat brain CCK-B receptor, with IC50 values approaching those of the commonly used antagonists L-365,260 and PD-134,308. Moreover, binding studies performed using transfected CHO cells showed that two affinity states of the CCK-B receptor can be discriminated by some of these compounds which also have different biological profiles and are therefore highly interesting tools for the biochemical and pharmacological characterization of CCK-B receptor heterogeneity.

Studies on conformational consequences of i to i + 3 side-chain cyclization in model cyclic tetrapeptides

In an effort to explore the effect of ring size on the biologically active conformation of cyclic analogs of the mating pheromone alpha-factor (WHWLQLKPGQPMY) from Saccharomyces cerevisiae, eight cyclic tetrapeptides corresponding to the KPGQ portion of alpha-factor were synthesized. These N-alpha-acetyl/carboxyl amide terminal cyclic tetrapeptides were prepared on a 4-methylbenzhydrylamine resin using orthogonal Boc, Fmoc, OFm and OtBut protecting groups and HOBt-DIPC accelerated active esters or urethane-protected N-carboxyanhydrides. On-resin cyclization of the side-chain amino and carboxyl groups of the first and fourth residues, respectively, was performed with the BOP reagent to generate lactams containing 14-18 atoms. HF cleavage resulted in two products, the desired cyclic tetrapeptide and a major side product. All peptides were purified to near homogeneity (> 99%) by using reversed-phase HPLC and were characterized by FBMS and 1H NMR. Certain constrained cyclic tetrapeptides appear to be a mixture of isomers at room temperature as evidenced by HPLC and NMR. The major side product has been identified as a cyclo dimer, obtained as a consequence of interchain cyclization on the resin. CD analysis in several solvents gives evidence that some of the cyclic tetrapeptides exist in beta-turn conformations.

Peptide mimetics as enzyme inhibitors: use of free energy perturbation calculations to evaluate isosteric replacement for amide bonds in a potent HIV protease inhibitor

We present the application of free energy perturbation theory/molecular dynamics to predict the consequence of replacing each of the seven peptide bonds in the potent HIV protease inhibitor JG365: ACE (acetyl)-Ser-Leu-Asn-HEA (hydroxyethylamine analog of Phe-Pro)-Ile-Val-NME (N-methyl) by ethylene or fluoroethylene isosteres. Replacing two of these bonds may well lead to significantly tighter binding; replacing two others is predicted to significantly diminish the binding affinity. Also, for three of the peptide bonds fluoroethylene replacements could lead to increased binding of free energies of the inhibitors. Our results should be considered as predictive since there are, as yet, no experimental results on such peptide replacements as enzyme inhibitors.

The structure of neutral protease from Bacillus cereus at 0.2-nm resolution

The crystal structure of the neutral protease from Bacillus cereus has been refined to an R factor of 17.5% at 0.2-nm resolution. The enzyme, an extracellular metalloendopeptidase, consists of two domains and binds one zinc and four calcium ions. The structure is very similar to that of thermolysin, with which the enzyme shares 73% amino-acid sequence identity. The active-site cleft between the two domains is wider in neutral protease than in thermolysin. This suggests the presence of a flexible hinge region between the two domains, which may assist enzyme action. The high-resolution analysis allows detailed examination of possible causes for the difference in thermostability between neutral protease and thermolysin.