Potent dibasic GPIIb/IIIa antagonists with reduced prolongation of bleeding time: synthesis and pharmacological evaluation of 2-oxopiperazine derivatives

Peptidomimetic Small-Molecule Inhibitors of 3CLPro Activity and Spike-ACE2 Interaction: Toward Dual-Action Molecules against Coronavirus Infections

The development of molecules able to target protein-protein interactions (PPIs) is of interest for the development of novel therapeutic agents. Since a high percentage of PPIs are mediated by α-helical structure at the interacting surface, peptidomimetics that reproduce the essential conformational components of helices are useful templates for the development of PPIs inhibitors. In this work, the synthesis of a constrained dipeptide isostere and insertion in the short peptide epitope EDLFYQ of the angiotensin-converting enzyme 2 (ACE2) α1 helix domain resulted in the identification of a molecule capable of inhibiting the SARS-CoV-2 ACE2/spike interaction in the micromolar range. Moreover, inhibition of SARS-CoV-2 3CLPro main protease activity was assessed as an additional inhibitory property of the synthesized peptidomimetics, taking advantage of the C-terminal Q amino acid present in both the ACE2 epitope and the Mpro recognizing motif (APSTVxLQ), thus paving the way to the development of multitarget therapeutics toward coronavirus infections.

Regioselective addition of Grignard reagents to N-acylpyrazinium salts: synthesis of substituted 1,2-dihydropyrazines and Δ5-2-oxopiperazines

The regioselective addition of Grignard reagents to mono- and disubstituted N-acylpyrazinium salts affording substituted 1,2-dihydropyrazines in modest to excellent yields (45–100%) is described. Under acidic conditions, these 1,2-dihydropyrazines can be converted to substituted Δ⁵-2-oxopiperazines providing a simple and efficient approach towards their preparation.

Synthesis of 1- and 4-substituted piperazin-2-ones via Jocic-type reactions with N-substituted diamines

Enantiomerically-enriched trichloromethyl-containing alcohols are transformed regioselectively into enantiomerically-enriched 1-substituted piperazinones by modified Jocic reactions.

Rational design of topographical helix mimics as potent inhibitors of protein-protein interactions

Protein–protein interactions encompass large surface areas, but often a handful of key residues dominate the binding energy landscape. Rationally designed small molecule scaffolds that reproduce the relative positioning and disposition of important binding residues, termed “hotspot residues”, have been shown to successfully inhibit specific protein complexes. Although this strategy has led to development of novel synthetic inhibitors of protein complexes, often direct mimicry of natural amino acid residues does not lead to potent inhibitors. Experimental screening of focused compound libraries is used to further optimize inhibitors but the number of possible designs that can be efficiently synthesized and experimentally tested in academic settings is limited. We have applied the principles of computational protein design to optimization of nonpeptidic helix mimics as ligands for protein complexes. We describe the development of computational tools to design helix mimetics from canonical and noncanonical residue libraries and their application to two therapeutically important protein–protein interactions: p53-MDM2 and p300-HIF1α. The overall study provides a streamlined approach for discovering potent peptidomimetic inhibitors of protein–protein interactions.

Synthesis and library construction of privileged tetra-substituted Δ5-2-oxopiperazine as β-turn structure mimetics

In this study, we developed an efficient and practical procedure for the synthesis of tetra-substituted Δ5-2-oxopiperazine that mimics the bioactive β-turn structural motif of proteins. This synthetic route is robust and modular enough to accommodate four different substituents to obtain a high level of molecular diversity without any deterioration in stereochemical enrichment of the natural and unnatural amino acids. Through the in silico studies, including a distance calculation of side chains and a conformational overlapping of our model compound with a native β-turn structure, we successfully demonstrated the conformational similarity of tetra-substituted Δ5-2-oxopiperazine to the β-turn motif. For the library construction in a high-throughput manner, the fluorous tag technology was adopted with the use of a solution-phase parallel synthesis platform. A 140-membered pilot library of tetra-substituted Δ5-2-oxopiperazines was achieved with an average purity of 90% without further purification.

Practical Solid-Phase Parallel Synthesis of Δ5-2-Oxopiperazines via N-Acyliminium Ion Cyclization

A practical solid-phase strategy for the synthesis of Delta(5)-2-oxopiperazines via N-acyliminium ion cyclization has been developed. A key step in the library synthesis is tandem acidolytic cleavage with subsequent in situ iminium formation, followed by stable enamide transformation. This approach is exemplified by the preparation of a 192-member pilot library using bromoacetal resins without further purification.

Simple, versatile and highly diastereoselective synthesis of 1,3,4-trisubstituted-2-oxopiperazine-containing peptidomimetic precursors

The selective O-deprotection of (1'S)-4-(tert-butoxycarbonyl)-1-[1'-phenylmethyloxymethyl-2'-[(tert-butyldimethylsilyl)oxy]ethyl]-2-oxopiperazine furnished an enantiomerically pure alcohol whose regio- and diastereoselective C3-alkylation yielded either (3R)- or (3S)-1,3,4-trisubstituted-2-oxopiperazines in high diastereomeric purity. These derivatives were efficiently transformed into (1'R)- or (1'S)-peptide templates utilizable to prepare peptidomimetics. This method provides easy access to each 1,3,4-trisubstituted-2-oxopiperazine diastereomer and facilitates, through the large choice of substituents at the 3-position together with the chemistry that can be performed on the N1 substituent, the preparation of a large number of diastereomerically pure constrained peptidomimetics from a single precursor.

Pyridazines. Part 36: Synthesis and antiplatelet activity of 5-substituted-6-phenyl-3(2H)-pyridazinones

A convenient and efficient palladium-catalysed retro-ene-assisted method has been developed to prepare a series of 5-substituted-6-phenyl-3(2H)-pyridazinones as potential antiplatelet drugs. The most active compounds were those that contain a 3-phenyl-3-oxo-propenyl fragment or a phenylthio group at position 5 of the heterocyclic ring.

Pyridazines. Part 28: 5-alkylidene-6-phenyl-3(2H)-pyridazinones, a new family of platelet aggregation inhibitors

The synthesis and anti-platelet activity of several 5-alkylidene-6-phenyl-3(2H)-pyridazinones are described. The most active compounds are those that contain oxygenated functions (COOR, COMe) on the alkylidene fragment (6a, 6b and 6c).