Synthesis and Analysis of the Conformational Preferences of 5-Aminomethyloxazolidine-2,4-dione Scaffolds: First Examples of β2- and β2, 2-Homo-Freidinger Lactam Analogues

Design of κ-Opioid Receptor Agonists for the Development of Potential Treatments of Pain with Reduced Side Effects

The κ-opioid receptor (KOR) has recently emerged as an alternative therapeutic target for the development of pain medications, without deleterious side effects associated with the μ-opioid receptor (MOR). However, modulation of KOR is currently under investigation for the treatment of depression, mood disorders, psychiatric comorbidity, and specific drug addictions. However, KOR agonists also trigger adverse effects including sedation, dysphoria, and hallucinations. In this respect, there is currently much debate on alternative paradigms. Recent effort has been devoted in search of biased ligands capable of selectively activating favorable signaling over signaling associated with unwanted side effects. On the other hand, the use of partial agonists is expected to allow the analgesia to be produced at dosages lower than those required to produce the adverse effects. More empirically, the unwanted central effects can be also avoided by using peripherally restricted agonists. In this review, we discuss the more recent trends in the design of KOR-selective, biased or partial, and finally, peripherally acting agonists. Special emphasis is given on the discussion of the most recent approaches for controlling functional selectivity of KOR-specific ligands.

Heterocycles as a Peptidomimetic Scaffold: Solid-Phase Synthesis Strategies

Peptidomimetics are a privileged class of pharmacophores that exhibit improved physicochemical and biological properties. Solid-phase synthesis is a powerful tool for gaining rapid access to libraries of molecules from small molecules to biopolymers and also is widely used for the synthesis of peptidomimetics. Small molecules including heterocycles serve as a core for hundreds of drugs, including peptidomimetic molecules. This review covers solid-phase synthesis strategies for peptidomimetics molecules based on heterocycles.

Integrin-Targeting Peptides for the Design of Functional Cell-Responsive Biomaterials

Integrins are a family of cell surface receptors crucial to fundamental cellular functions such as adhesion, signaling, and viability, deeply involved in a variety of diseases, including the initiation and progression of cancer, of coronary, inflammatory, or autoimmune diseases. The natural ligands of integrins are glycoproteins expressed on the cell surface or proteins of the extracellular matrix. For this reason, short peptides or peptidomimetic sequences that reproduce the integrin-binding motives have attracted much attention as potential drugs. When challenged in clinical trials, these peptides/peptidomimetics let to contrasting and disappointing results. In the search for alternative utilizations, the integrin peptide ligands have been conjugated onto nanoparticles, materials, or drugs and drug carrier systems, for specific recognition or delivery of drugs to cells overexpressing the targeted integrins. Recent research in peptidic integrin ligands is exploring new opportunities, in particular for the design of nanostructured, micro-fabricated, cell-responsive, stimuli-responsive, smart materials.

Integrin-Targeting Dye-Doped PEG-Shell/Silica-Core Nanoparticles Mimicking the Proapoptotic Smac/DIABLO Protein

Cancer cells demonstrate elevated expression levels of the inhibitor of apoptosis proteins (IAPs), contributing to tumor cell survival, disease progression, chemo-resistance, and poor prognosis. Smac/DIABLO is a mitochondrial protein that promotes apoptosis by neutralizing members of the IAP family. Herein, we describe the preparation and in vitro validation of a synthetic mimic of Smac/DIABLO, based on fluorescent polyethylene glycol (PEG)-coated silica-core nanoparticles (NPs) carrying a Smac/DIABLO-derived pro-apoptotic peptide and a tumor-homing integrin peptide ligand. At low μM concentration, the NPs showed significant toxicity towards A549, U373, and HeLa cancer cells and modest toxicity towards other integrin-expressing cells, correlated with integrin-mediated cell uptake and consequent highly increased levels of apoptotic activity, without perturbing cells not expressing the α5 integrin subunit.

Constraining Endomorphin-1 by β,α-Hybrid Dipeptide/Heterocycle Scaffolds: Identification of a Novel κ-Opioid Receptor Selective Partial Agonist

Herein we present the expedient synthesis of endomorphin-1 analogues containing stereoisomeric β²-homo-Freidinger lactam-like scaffolds ([Amo²]EM), and we discuss opioid receptor (OR) affinity, enzymatic stability, functional activity, in vivo antinociceptive effects, and conformational and molecular docking analysis. Hence, H-Tyr-Amo-Trp-PheNH₂ resulted to be a new chemotype of highly stable, selective, partial KOR agonist inducing analgesia, therefore displaying great potential interest as a painkiller possibly with reduced harmful side effects.

Modern tools for the chemical ligation and synthesis of modified peptides and proteins

The ability to improve nature's capacity by introducing modification of biological interest in proteins and peptides (P&P) is one of the modern challenges in synthetic chemistry. Due to the unfavorable pharmacokinetic properties, many native P&P are of little use as therapeutic agents. Today, few methods for the preparation of modified proteins are available. Initially introduced to realize the ligation between two standard peptidic sequences, and hence to afford native proteins, the modern chemical methodologies, in other words native chemical ligation, expressed ligation, Staudinger ligation, auxiliary mediated ligation, aldehyde capture, etc., can be virtually utilized to ligate a variety of peptidomimetic partners, allowing a systematic access to modified, unnatural large P&P.

5-aminomethyloxazolidine-2,4-dione hybrid α/β-dipeptide scaffolds as inductors of constrained conformations: Applications to the synthesis of integrin antagonists

Peptidomimetics represent an attractive starting point for drug discovery programs; in particular, peptidomimetics that result from the incorporation of a heterocycle may take advantage of increased enzymatic stability and higher ability to reproduce the bioactive conformations of the parent peptides, resulting in enhanced therapeutic potential. Herein, we present mimetics of the α4β1 integrin antagonist BIO1211 (MPUPA-Leu-Asp-Val-Pro-OH), containing a aminomethyloxazolidine-2,4-dione scaffold (Amo). Interestingly, the retro-sequences PhCOAsp(OH)-Amo-APUMP including either (S)- or (R)-configured Amo displayed significant ability to inhibit the adhesion of α4β1 integrin expressing cells, and remarkable stability in mouse serum. Possibly, the conformational bias exerted by the Amo scaffold determined the affinity for the receptors. These peptidomimetics could be of interest for the development of small-molecule agents effective against inflammatory processes and correlated autoimmune diseases.

Integrin Ligands with α/β-Hybrid Peptide Structure: Design, Bioactivity, and Conformational Aspects

Integrins are cell surface receptors for proteins of the extracellular matrix and plasma-borne adhesive proteins. Their involvement in diverse pathologies prompted medicinal chemists to develop small-molecule antagonists, and very often such molecules are peptidomimetics designed on the basis of the short native ligand-integrin recognition motifs. This review deals with peptidomimetic integrin ligands composed of α- and β-amino acids. The roles exerted by the β-amino acid components are discussed in terms of biological activity, bioavailability, and selectivity. Special attention is paid to the synthetic accessibility and efficiency of conformationally constrained heterocyclic scaffolds incorporating α/β-amino acid span.