Donatella Potenza

conformational preferences of peptides containing reverse-turn mimetic bicyclic lactams: inverse γ-turns versus type-ii′ β-turns — insights into β-hairpin stability.

The solid-phase synthesis and characterization of a series of peptides (3–9), containing reverse-turn mimetic bicyclic lactams (1a, 1b), was reported in the preceding paper. The bicyclic lactams (1a, 1b) possess high structural similarity to the two central residues of a β-turn. The conformational preferences of the constrained peptides have been investigated by NMR spectroscopy and IR spectroscopy. Our experimental results have been complemented by computer modelling studies and show that the constrained peptides (3–9) form an inverse γ-turn or a type-II′ β-turn through intramolecular hydrogen bonding, depending on the nature of the reverse-turn mimic. In N-acetylated tetrapeptide mimics incorporating the two different bicyclic lactams (a series and b series), H5 is available for either a γ-turn (7-membered ring with the carbonyl group of the bicyclic lactam) or a β-turn (10-membered ring with the carbonyl group of residue 2), as shown in Figures 7 and 9. The a series incorporating the (5,7)-bicyclic lactam predominantly induces the γ-turn conformation, while the b series incorporating the (5,6)-bicyclic lactam can promote either a γ-turn or a β-turn conformation, with the β-turn usually being preferred and with varying degrees of β-hairpin formation.

Stereoselective synthesis of statin analogues.

Abstract Statin analogues can be synthesized stereoselectively (diastereomeric ratios up to 4:1) starting from malic acid. The key step involves an unprecedented cis-selective allylation of an α-alkoxy N-acyliminium ion.

Synthesis of Novel DC-SIGN Ligands with an α-Fucosylamide Anchor

The dendritic cell‐specific intercellular adhesion molecule (ICAM) 3‐grabbing nonintegrin (DC‐SIGN) is a C‐type lectin that appears to perform several different functions. Besides mediating adhesion between dendritic cells and T lymphocytes, DC‐SIGN recognizes several pathogens some of which, including HIV, appear to exploit it to invade host organisms. The intriguing diversity of the roles attributed to DC‐SIGN and their therapeutic implications have stimulated the search for new ligands that could be used as biological probes and possibly as lead compounds for drug development. The natural ligands of DC‐SIGN consist of mannose oligosaccharides or fucose‐containing Lewis‐type determinants. Using the known 3D structure of the Lewis‐x trisaccharide, we have identified some monovalent α‐fucosylamides that bind to DC‐SIGN with inhibitory constants 0.4–0.5 mM, as determined by SPR, and have characterized their interaction with the protein by STD NMR spectroscopy. This work establishes for the first time α‐fucosylamides as functional mimics of chemically and enzymatically unstable α‐fucosides and describes interesting candidates for the preparation of multivalent systems able to block the receptor DC‐SIGN with high affinity and with potential biomedical applications.

Cyclic RGD-Peptidomimetics Containing Bifunctional Diketopiperazine Scaffolds as New Potent Integrin Ligands

The synthesis of eight bifunctional diketopiperazine (DKP) scaffolds is described; these were formally derived from 2,3-diaminopropionic acid and aspartic acid (DKP-1-DKP-7) or glutamic acid (DKP-8) and feature an amine and a carboxylic acid functional group. The scaffolds differ in the configuration at the two stereocenters and the substitution at the diketopiperazinic nitrogen atoms. The bifunctional diketopiperazines were introduced into eight cyclic peptidomimetics containing the Arg-Gly-Asp (RGD) sequence. The resulting RGD peptidomimetics were screened for their ability to inhibit biotinylated vitronectin binding to the purified integrins α(v)β(3) and α(v)β(5), which are involved in tumor angiogenesis. Nanomolar IC(50) values were obtained for the RGD peptidomimetics derived from trans DKP scaffolds (DKP-2-DKP-8). Conformational studies of the cyclic RGD peptidomimetics by (1)H NMR spectroscopy experiments (VT-NMR and NOESY spectroscopy) in aqueous solution and Monte Carlo/Stochastic Dynamics (MC/SD) simulations revealed that the highest affinity ligands display well-defined preferred conformations featuring intramolecular hydrogen-bonded turn motifs and an extended arrangement of the RGD sequence [Cβ(Arg)-Cβ(Asp) average distance ≥8.8 Å]. Docking studies were performed, starting from the representative conformations obtained from the MC/SD simulations and taking as a reference model the crystal structure of the extracellular segment of integrin α(v)β(3) complexed with the cyclic pentapeptide, Cilengitide. The highest affinity ligands produced top-ranked poses conserving all the important interactions of the X-ray complex.

A new method for the solution and solid phase synthesis of chiral β-sulfonopeptides under mild conditions

Abstract Chiral β-sulfonopeptides were synthesized both in solution and in the solid phase using the sulfonyl chlorides derived from enantiomerically pure 2-substituted taurines under mild coupling conditions [cat. 4-dimethylaminopyridine (DMAP) and excess methyl trimethylsilyl dimethylketene acetal (MTDA) as a proton trap].

Biological and molecular properties of a new αvβ3/αvβ5 integrin antagonist

The aim of the present study was to identify specific αvβ3/αvβ5 integrin antagonists active on tumor-induced angiogenesis. To this purpose, in vitro integrin-binding assays were used to screen a library of conformationally constrained bicyclic lactam Arg-Gly-Asp–containing pseudopeptides. The results identified ST1646 as a high-affinity specific ligand for αvβ3 and αvβ5 integrins with negligible interacting with α5β1 integrin. In all the assays, ST1646 was equipotent to or more potent than the well-characterized integrin antagonists c(RGDfV) and cyclo(Arg-Gly-Asp-d-Phe-[NMe]Val) (EMD121974). In the chorioallantoic membrane assay, topical administration of ST1646 was able to prevent the angiogenic responses elicited by recombinant fibroblast growth factor-2 or vascular endothelial growth factor. In addition, systemic administration of ST1646 in mice exerted a significant antiangiogenic activity on neovascularization triggered by mammary carcinoma MDA-MB435 cells implanted s.c. in a dorsal air sac via a (Millipore Filter Corporation, Bedford, MA) chamber. Moreover, ST1646 delivery via an osmotic pump inhibited the growth and vascularization of tumor xenografts originating from the injection of αvβ3/αvβ5-expressing human ovarian carcinoma cells in nude mice. In agreement with the biochemical and pharmacologic studies, Monte Carlo/Stochastic Dynamics simulation showed that the bicyclic scaffold in ST1646 forced the compound to assume a preferred conformation superimposable to the X-ray conformation of αvβ3-bound EMD121974. Accordingly, computer-docking studies indicated that the ST1646-αvβ3 integrin complex maintains the ligand-receptor distances and interactions observed in the crystalline EMD121974-αvβ3 integrin complex. Taken together, these observations indicate that ST1646 represents a dual αvβ3/αvβ5 integrin antagonist with interesting biochemical and biological features to be tested in cancer therapy.

Conformational Analysis of Azabicycloalkane Amino Acid Scaffolds as Reverse-Turn Inducer Dipeptide Mimics

In an effort to design structural mimics of protein and peptide reverse-turns, the conformations of 5,5-, 6,5-, and 7,5-fused 1-aza-2-oxobicycloalkane amino acids have been evaluated. The conformational preferences of these proline-derived bicyclic lactams have been studied by Monte Carlo molecular mechanics searches, and the reverse-turn inducing properties of the calculated structures have been quantitatively assessed using various geometrical parameters. All of the four possible diastereoisomers arising from two of the three stereogenic centres [C3 and bridgehead carbon atom; Pro Cα is (S) in all compounds] have been considered for each bicyclic scaffold. These studies have revealed that the (3S)-Pro Cα(S) configuration is an effective turn-inducer, although the torsion angles of the backbone do not always mimic those of classical β-turns. A dependence of the turn-inducing ability on lactam ring size and bridgehead stereochemistry has also been found. Reverse-turn mimetic bicyclic lactams have been shown to exhibit a tendency to form an inverse γ-turn or a type II′ β-turn. Experimental 1H-NMR and FT-IR spectroscopic data of model compounds in chloroform solutions have complemented our computer modelling studies and have confirmed our conclusions.

Hydrogen-Bonding Donor/Acceptor Scales inβ-Sulfonamidopeptides

The conformational preferences of β-sulfonamidopeptides (for example 1) in chloroform solution were investigated by variable-temperature 1H NMR spectroscopy and FT-IR spectroscopy. The following hydrogen-bonding acceptor scale was derived from the experiments: RCON≈tBuOCON>COOMe≥RSO2N.

Cyclic RGD‐Containing Functionalized Azabicycloalkane Peptides as Potent Integrin Antagonists for Tumor Targeting

Vitronectin receptors αvβ3 and αvβ5 have emerged as potential therapeutic targets for the treatment of osteoporosis, restenosis, ocular disease, tumor‐induced angiogenesis, metastasis, and sickle‐cell anemia. Among a collection of compounds, a new potent integrin antagonist was synthesized, and its binding toward the αvβ3 and αvβ5 receptors was evaluated. This molecule is a suitable candidate as a vector for therapeutics and diagnostics.

Rational design, synthesis and characterization of potent, non-peptidic Smac mimics/XIAP inhibitors as proapoptotic agents for cancer therapy

Novel proapoptotic Smac mimics/IAPs inhibitors have been designed, synthesized and characterized. Computational models and structural studies (crystallography, NMR) have elucidated the SAR of this class of inhibitors, and have permitted further optimization of their properties. In vitro characterization (XIAP BIR3 and linker-BIR2-BIR3 binding, cytotox assays, early ADMET profiling) of the compounds has been performed, identifying one lead for further in vitro and in vivo evaluation.