Synthesis of Pyridazine-Based α-Helix Mimetics

Emerging therapeutics: The imidazo[1,2-b]pyridazine scaffold as a novel drug candidate for eumycetoma, a neglected tropical disease

Mycetoma is a neglected invasive infection endemic in tropical and subtropical regions, presenting as a chronic subcutaneous inflammatory mass that can spread to deeper structures, leading to deformities, disabilities, and potentially mortality. The current treatment of eumycetoma, the fungal form of mycetoma, involves antifungal agents, such as itraconazole, combined with surgical intervention. However, this approach has limited success, with low cure rates and a high risk of recurrence. This study addresses to the urgent need for more effective therapeutics by designing and synthesising 47 diversely pharmacomodulated imidazo [1,2-b]pyridazine derivatives using a simple synthetic pathway with good yields and purity. Of these, 17 showed promising in vitro activity against Madurella mycetomatis, the prime causative agent of eumycetoma, with IC50 ≤ 5 μM and demonstrated significantly lower cytotoxicity compared to standard treatments in NIH-3T3 fibroblasts. Notably, compound 14d exhibited an excellent activity with an IC50 of 0.9 μM, in the same order then itraconazole (IC50 = 1.1 μM), and achieved a favourable selectivity index of 16 compared to 0.8 for itraconazole. These promising results warrant further research to evaluate the clinical potential of these novel compounds as safer, more effective treatments for eumycetoma, thus addressing a profound gap in current therapeutic strategies.

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.

A Modular Synthesis of Teraryl-Based α-Helix Mimetics, Part 5: A Complete Set of Pyridine Boronic Acid Pinacol Esters Featuring Side Chains of Proteinogenic Amino Acids

Teraryl-based α-helix mimetics have proven to be useful compounds for the inhibition of protein-protein interactions (PPI). We have developed a modular and flexible approach for the synthesis of teraryl-based α-helix mimetics using pyridine containing boronic acid building blocks to increase the water solubility. Following our initial publication in which we have introduced the methodology in combination with sequential Pd-catalyzed cross-coupling for teraryl assembly, we can now report a complete set of pyridine based boronic acid building blocks decorated with side chains of all proteinogenic amino acids relevant for PPI (Ala, Arg, Asn, Asp, Cys, Gln, Glu, His, Ile, Leu, Lys, Met, Phe, Ser, Thr, Trp, Tyr, Val) to complement the core fragment set. For a representative set of teraryls we have studied the influence of the pyridine rings on the solubility of the assembled oligoarenes.

Synthesis of 1,4,5,6-tetrahydropyridazines and pyridazines via transition-metal-free (4 + 2) cycloaddition of alkoxyallenes with 1,2-diaza-1,3-dienes

We developed an economical and practical protocol for the synthesis of 1,4,5,6-tetrahydropyridazines. A diverse range of alkoxyallenes and 1,2-diaza-1,3-dienes undergo (4 + 2) cycloaddition to generate the desired products in excellent yields. The high efficiency, wide substrate scope and good functional group tolerance of this process, coupled with operational simplicity, render the method synthetically attractive. The utility of the cycloaddition is also demonstrated by the preparation of various pyridazines from 1,4,5,6-tetrahydropyridazines.

We developed an economical and practical protocol for the synthesis of 1,4,5,6-tetrahydropyridazines and pyridazines via cyclization of alkoxyallenes and 1,2-diaza-1,3-dienes.

Using Peptidomimetics and Constrained Peptides as Valuable Tools for Inhibiting Protein⁻Protein Interactions

Protein–protein interactions (PPIs) are tremendously important for the function of many biological processes. However, because of the structure of many protein–protein interfaces (flat, featureless and relatively large), they have largely been overlooked as potential drug targets. In this review, we highlight the current tools used to study the molecular recognition of PPIs through the use of different peptidomimetics, from small molecules and scaffolds to peptides. Then, we focus on constrained peptides, and in particular, ways to constrain α-helices through stapling using both one- and two-component techniques.