Investigation of the interaction between the atypical agonist c[YpwFG] and MOR.

Endogenous and exogenous opiates are currently considered the drugs of choice for treating different kinds of pain. However, their prolonged use produces several adverse symptoms, and in addition, many forms of pain are resistant to any kind of therapy. Therefore, the discovery of compounds active towards mu-opioid receptors (MORs) by alternative pharmacological mechanisms could be of value for developing novel classes of analgesics. There is evidence that some unusual molecules can bind opioid receptors, albeit lacking some of the typical opioid pharmacophoric features. In particular, the recent discovery of a few compounds that showed agonist behavior even in the absence of the primary pharmacophore, namely a protonable amine, led to a rediscussion of the importance of ionic interactions in stabilizing the ligand-receptor complex and in activating signal transduction. Very recently, we synthesized a library of cyclic analogs of the endogenous, MOR-selective agonist endomorphin-1 (YPWF-NH(2)), containing a Gly5 bridge between Tyr1 and Phe4. The cyclopeptide c[YpwFG] showed good affinity and agonist behavior. This atypical MOR agonist does not have the protonable Tyr amine. In order to gain more information about plausible mechanisms of interaction between c[YpwFG] and the opioid receptor, we synthesized a selected set of derivatives containing different bridges between Tyr1 and Phe4, and tested their affinities towards mu-opioid receptors. We performed conformational analysis of the cyclopeptides by NMR spectroscopy and molecular dynamics, and investigated plausible, unprecedented modes of interaction with the MOR by molecular docking. The successive quantum mechanics/molecular mechanics investigation of the complexes obtained by the molecular docking procedure furnished a more detailed description of the binding mode and the electronic properties of the ligands. The comparison with the binding mode of the potent agonist JOM-6 seems to indicate that the cyclic endomorphin-1 analogs interact with the receptor by way of an alternative mechanism, still maintaining the ability to activate the receptor.

Synthesis of dehydro-beta-amino esters via highly regioselective amination of allylic carbonates.

The allylic amination of acetates and carbonates affords dehydro-beta-aminoesters, which are useful precursors of biologically active compounds. The uncatalyzed reaction proceeds via a S(N)2' mechanism. On the other hand, under palladium-catalyzed conditions, the reaction shows a strong solvent-dependent regiocontrol, affording exclusively one of the two possible regioisomers with complete transfer of chirality from the substrates to the products.

A novel family of minimal PMRI cyclic peptides as versatile scaffolds for generating new molecular topology.

The surface loops of proteins and active peptides are implicated in the activation of biological responses upon recognition by enzymes and receptors. Obviously, it is of interest to investigate these loops as potential leads for drug discovery. Currently, there is an urgent need for novel, general, and conformationally definite cyclic peptidomimetic scaffolds capable to mimic small portions of the protein surface. In this respect, 13-membered ring peptidomimetics can be considered privileged structures, since they represent the smallest possible systems that can retain all of the features of organized protein structures, such as single H-bonded alfa-helix loops and different kind of turns. In the present work, we report a novel family of 13-membered ring cyclic peptidomimetics based on a minimal PMRI (partially modified retro-inverse) peptide strategy; in particular, we describe the synthesis and the conformational analysis of a representative member of the family. These scaffolds have been designed to permit easy introduction in a combinatorial fashion of a range of pharmacophores that possess a diversity of structure, function, and 3D disposition.

Highly diastereoselective allylic azide formation and isomerization. Synthesis of 3(2'-amino)-beta-lactams.

The stereoselective anti SN2' attack of NaN3 to 3-alkenyl-3-bromo-azetidin-2-ones gave a mixture of diastereomeric azides in fast equilibrium. The [3,3]-sigmatropic rearrangement of allylic azides occurred with complete stereocontrol, allowing the equilibrium to be directed preferentially toward the (E)- or (Z)-isomer, useful precursors of 3(2'-amino)-beta-lactams. [reaction: see text]

Endomorphin-1 analogues containing beta-proline are mu-opioid receptor agonists and display enhanced enzymatic hydrolysis resistance.

In this paper we describe the synthesis and affinity toward the mu-opioid receptor of some tetrapeptides obtained from endomorphin-1, H-Tyr-Pro-Trp-Phe-NH(2) (1), by substituting each amino acid in turn with its homologue. The ability to bind mu-opioid receptors depends on the beta-amino acid, and in particular 4, which contains beta-L-Pro, has a K(I) in the nanomolar range. The peptides 4 and 5 are significantly more resistant to enzymatic hydrolysis than 1. The same compounds, as well as the mu-opioid receptor agonist DAMGO, produced a concentration-dependent inhibition of forskolin-stimulated cyclic AMP formation, thus behaving as mu-opioid agonists. These features suggest that this novel class of endomorphin-1 analogues may represent suitable candidates for the in vivo investigation as potential mu-opioid receptor agonists.

Synthesis and evaluation of the affinity toward mu-opioid receptors of atypical, lipophilic ligands based on the sequence c[-Tyr-Pro-Trp-Phe-Gly-].

An ultimate and general model describing the interaction between opioid ligands and mu-opioid receptors is not available yet, so the mode of action of atypical peptide analogues or peptidomimetics is worthy of investigation. In this context, the peptide c[-Tyr-d-Pro-d-Trp-Phe-Gly-] was observed to act as an agonist toward mu-opioid receptors with appreciable potency, albeit deprived of a protonable nitrogen. This compound was synthesized as a member of a library of diastereo- or enantiomeric cyclic peptides based on the sequence of endomorphin-1, aiming to obtain lipophilic peptide ligands active at the mu-opioid receptors, having good performances in terms of resistance to enzymatic degradation and permeation of biological barriers.

Antinociception by a peripherally administered novel endomorphin-1 analogue containing beta-proline.

We previously described a novel endomorphin-1 analogue (Tyr-L-beta-Pro-Trp-Phe-NH(2); Endo1-beta-Pro) more resistant to enzymatic hydrolysis than endomorphin-1 that acts as a mu-opioid receptor agonist. In this study we report that Endo1-beta-Pro, s.c. injected in the mouse, is an effective antinociceptive agent in the tail flick (ED(50)=9.2 mg/kg) and acetic acid-induced abdominal constriction (ED(50)=1.2 mg/kg) tests. Moreover, s.c. Endo1-beta-Pro significantly decreases, in the mouse, the gastrointestinal propulsion measured as transit of an orally administered charcoal meal (ED(50)=10.0 mg/kg). Subcutaneous beta-funaltrexamine or a high dose of the mu(1)-opioid receptor-selective antagonist naloxonazine (50 mg/kg) prevents the antinociceptive and antitransit action of Endo1-beta-Pro; moreover, these effects are partially blocked by i.c.v. naloxone or by i.p. naloxone methiodide, this latter does not readily cross the blood-brain barrier. On the contrary, the kappa-opioid receptor antagonist nor-binaltorphimine or the delta-opioid receptor antagonist naltrindole are ineffective Thus, Endo1-beta-Pro may act, preferentially, through central and peripheral mu(2)-opioid receptors to produce antinociception and to inhibit gastrointestinal transit. Endo1-beta-Pro is among the first endomorphin-1 analogues showing antinociceptive activity after systemic administration. This compound will be extremely useful for exploring the pharmacological profile of endomorphins in vivo and confirms the potential therapeutic interest of endomorphin derivatives as novel analgesic agents.

Antiangiogenic effect of dual/selective alpha(5)beta(1)/alpha(v)beta(3) integrin antagonists designed on partially modified retro-inverso cyclotetrapeptide mimetics.

Recent evidence highlighted the role of alpha(5)beta(1) integrin in angiogenesis and in regulating alpha(v)beta(3) integrin function. As a consequence, selective alpha(5)beta(1) integrin inhibitors or dual alpha(5)beta(1)/alpha(v)beta(3) integrin inhibitors are considered promising candidates for the development of cancer therapeutic agents. In this paper, we describe the synthesis and pharmacological characterization of a minilibrary of cyclotetrapeptide mimetics containing a PMRI Arg-Gly-Asp sequence. In particular, c[(R)-betaPhepsi(NHCO)Asppsi(NHCO)Gly-Arg] (3) displayed a good activity in inhibiting the alpha(v)beta(3) integrin-mediated cell adhesion of fibronectin or vitronectin, as well as the adhesion of fibronectin to the alpha(5)beta(1) integrin. Interestingly, the diastereomeric compound c[(S)-betaPhepsi(NHCO)Asppsi(NHCO)Gly-Arg] (2) maintained a good efficacy in inhibiting alpha(5)beta(1) integrin while gaining a certain selectivity over alpha(v)beta(3) integrin. These two integrin antagonists significantly inhibited bFGF-induced human endothelial cell tube formation at submicromolar concentrations. Conformational analysis and Molecular Docking calculations suggest that the different alpha(5)beta(1) versus alpha(v)beta(3) selectivity of 2 and 3 can be rationalized on the basis of the alternative display of the aromatic side chain adjacent to Asp.

Cyclopeptide analogs for generating new molecular and 3D diversity.

Cyclic peptides have been often utilized as metabolically stable, conformationally restricted mimics of different kinds of biologically active peptides, including peptide antibiotics, endogenous opioid peptides, integrin inhibitors, peptide hormones, anticancer peptides, and so on. And in particular, cyclic compounds which can mimic important secondary structure elements such as beta-turns are of outstanding importance. Since greater chemical and structural diversity are primary features to pursue for finding novel leads for pharmacological and biotechnological applications, we explored the potential utility of the retro-inverso modification. We introduced this modification into the sequence of 13-membered cyclotetrapeptides, which can be regarded as easily available, conformationally stable analogs of cyclotetrapeptides composed of all alpha-residues. In this paper we describe the synthesis of a selected mini-library of partially modified retro-inverso cyclic peptides as conformationally homogeneous scaffolds for medicinal chemistry applications. The different compounds have been obtained by simple scramble of the same residues. Finally, we discuss the conformational features of such molecules as turn mimics. The comparison suggests that the retro-inverso modification allows a higher degree of three-dimensional diversity than normal peptides.

Synthesis and conformational analysis of cyclotetrapeptide mimetic beta-turn templates and validation as 3D scaffolds.

The conformations of all stereoisomers of PMRI cyclotetrapeptide mimetics 1-8 are essentially determined by the predisposition of the diamine to stabilize beta-turns. The peptide mimetics can be regarded as 3D scaffolds for designing molecules with a predictable display of the pharmacophores. We used the models for testing novel RGD analogues as alpha(v)beta(3)-integrin receptor antagonists.

Synthesis and biological evaluation of unprecedented classes of spiro-beta-lactams and azido-beta-lactams as acyl-CoA:cholesterol acyltransferase inhibitors.

Unprecedented classes of four- and five-membered hydroxyl-spiro-beta-lactams and hydroxyl-azido-beta-lactams were prepared via regioselective ring opening of hydroxyl-epoxides. The potential of these particular beta-lactams as biologically active compounds has been confirmed by the results obtained in ACAT inhibition assays.

Inhibition of cancer cell adhesion by heterochiral Pro-containing RGD mimetics.

In this paper, we describe the synthesis of a selected library of heterochiral d-Pro-containing RGD-peptidomimetics (RpD) and we investigate the biological activity as inhibitors of fibronectin adhesion to SK-MEL-24 tumor cells. In particular, peptides 4 and 8 showed an IC(50) in the 10(-8)M range. Despite the linear structure, the peptides tend to adopt a folded conformation in a polar environment.

Synthesis and biological evaluation of non-peptide alpha(v)beta(3)/alpha(5)beta(1) integrin dual antagonists containing 5,6-dihydropyridin-2-one scaffolds.

Small constrained non-peptidic molecules consisting of a polyfunctionalized rigid core, carrying appendages corresponding to arginine and aspartic acid side chains, have been recently reported to be promising for drug development. In this work, the 5,6-dihydropyridin-2-one was envisaged as a scaffold to turn into potential integrin ligands, introducing a carboxylic acid and a basic appendage. The synthesis and the antiadhesion activity of a small library of peptidomimetics capable to recognize alpha(v)beta(3) and alpha(5)beta(1) integrins has been herein reported.

Synthesis and biological evaluation of azido- and aziridino-hydroxyl-beta-lactams through stereo- and regioselective epoxide ring opening.

Two new classes of azido- and aziridino-hydroxyl-beta-lactam containing structures have been prepared by means of a stereo- and regioselective epoxide ring opening. The straightforwardness of the procedure makes this strategy useful for the synthesis of potentially bioactive compounds. Some selected examples showed promising activity in acyl CoA-cholesterol acyltransferase inhibition assays.

Lewis acid-promoted synthesis and reactivity of beta-O-benzylhydroxylamino imides derived from D-glyceraldehyde.

This paper describes the synthesis and use of beta-hydroxylamino imides derived from D-glyceraldehyde possessing a number of reactive sites that operate synergistically or alternatively to bring about highly regio- and diastereoselective transformations to give an optically pure aziridine-2-imide, a dihydro pyrimidine-2,4-dione, or a lactone. Both the syntheses, via the diastereoselective 1,4-conjugate addition of O-benzyl hydroxylamine to alpha,beta-unsaturated imides, and transformations can be simply tuned by choosing between different Lewis acids.

Stability against enzymatic hydrolysis of endomorphin-1 analogues containing beta-proline.

The enantiomer of endomorphin-1 (Tyr-Pro-Trp-PheNH2) and the analogues containing (S)- or (R)-beta-proline have been synthesized, and their affinities towards mu-opioid receptors have been measured. As expected, the incubations of the different peptides with some commercially available enzymes showed that the presence of D-residues gave strong resistance towards digestion. The presence of beta-proline alone is sufficient to confer good resistance against the hydrolysis of the biologically strategic Pro-Trp bond.

Conformational analysis and mu-opioid receptor affinity of short peptides, endomorphin models in a low polarity solvent.

Peptide carbamates containing the sequence H-Pro-Trp-PheNH2 showed in CDCl3 restricted conformations stabilized by the presence of a gamma-turn. To test the reliability of the peptides as endomorphin conformational models, we measured the affinities for mu-receptors labelled with [3H]-DAMGO. In particular, Cbz-Pro-Trp-PheNH2 displayed a nanomolar affinity.