Design, synthesis and biological evaluation of 2,4-disubstituted oxazole derivatives as potential PDE4 inhibitors

Advances in pyrazolo[1,5-a]pyrimidines: synthesis and their role as protein kinase inhibitors in cancer treatment

Pyrazolo[1,5-a]pyrimidines are a notable class of heterocyclic compounds with potent protein kinase inhibitor (PKI) activity, playing a critical role in targeted cancer therapy. Protein kinases, key regulators in cellular signalling, are frequently disrupted in cancers, making them important targets for small-molecule inhibitors. This review explores recent advances in pyrazolo[1,5-a]pyrimidine synthesis and their application as PKIs, with emphasis on inhibiting kinases such as CK2, EGFR, B-Raf, MEK, PDE4, BCL6, DRAK1, CDK1 and CDK2, Pim-1, among others. Several synthetic strategies have been developed for the efficient synthesis of pyrazolo[1,5-a]pyrimidines, including cyclization, condensation, three-component reactions, microwave-assisted methods, and green chemistry approaches. Palladium-catalyzed cross-coupling and click chemistry have enabled the introduction of diverse functional groups, enhancing the biological activity and structural diversity of these compounds. Structure-activity relationship (SAR) studies highlight the influence of substituent patterns on their pharmacological properties. Pyrazolo[1,5-a]pyrimidines act as ATP-competitive and allosteric inhibitors of protein kinases, with EGFR-targeting derivatives showing promise in non-small cell lung cancer (NSCLC) treatment. Their inhibitory effects on B-Raf and MEK kinases are particularly relevant in melanoma. Biological evaluations, including in vitro and in vivo studies, have demonstrated their cytotoxicity, kinase selectivity, and antiproliferative effects. Despite these advances, challenges such as drug resistance, off-target effects, and toxicity persist. Future research will focus on optimizing synthetic approaches, improving drug selectivity, and enhancing bioavailability to increase clinical efficacy.

Rationale design and synthesis of new roflumilast analogues as preferential selective and potent PDE-4B inhibitors

In this study, we designed and synthesized novel analogues of roflumilast that exhibit selective inhibition of PDE-4B. To accomplish this target; synthesis of novel series (4a-u, 5a-i, and 6) was done, aiming at obtaining new PDE-4B inhibitors hits based on the proposed pharmacophore, 1-(cyclopropylmethoxy)-2-(difluoromethoxy) benzene moiety. Enzyme assay was used to measure the IC50 values for the PDE-4B inhibition of all the synthesized compounds along with roflumilast as a reference drug. The results demonstrated that most of the examined candidates exhibited considerable inhibitory activity against the PDE-4B enzyme. The four compounds (4i, 4k, 4p, and 4q) exhibited the highest potency (IC50 = 7.25, 7.15, 5.50, 7.19 nM, respectively) with no significant inhibition difference from roflumilast (no statistical difference at p < 0.05). Interestingly, compound 4p with 3-OH and 4-OCH3 substituents was found to be the most potent against PDE-4B enzyme (IC50 = 5.50 nM), compared to that of roflumilast (IC50 = 2.36 nM). Moreover, the most potent derivatives 4i, 4k, 4p, and 4q were further tested for PDE-4D inhibitory activity to investigate their PDE-4D/PDE-4B selectivity ratio. Compound 4k showed the highest selectivity towards PDE-4B isozyme more than the reference drug roflumilast (PDE-4D/4B IC50 ratio for compound 4k and roflumilast = 3.22 and 3.02, respectively). Additionally, compound 4p was chosen to test its selectivity for PDE-4B over PDE-8A, PDE-11A, and PDE-1B compared to thereference drug roflumilast. Compound 4p showed approximately 6-fold selectivity for PDE-4B over PDE-8A, about 5-fold selectivity for PDE-4B over PDE-11A, and about 11-fold selectivity of PDE-4B over PDE-1B. Compound 4p showed a higher selectivity towards PDE-4B than PDE-1B, more than the reference compound roflumilast. Furthermore, the most potent compounds (4i, 4k, 4p, 4q) were subjected to further investigation, and their effects on the cAMP level and percentage of inhibition of tumor necrosis factor-alpha (TNF-α) were studied and compared with reference drug roflumilast. Compound 4q showed the highest increase in the level of intracellular cAMP (6.55 ± 0.37 pmol/mL) and compound 4i showed the highest % of TNF-α inhibition (77.22 %). On the other side, a molecular docking study against PDE-4B clarified that all the examined candidates achieved nearly similar binding modes with similar orientations to that of the native roflumilast ligand and showed higher docking scores than roflumilast.

PDE4 inhibitors for disease therapy: advances and future perspective

The PDE4 enzyme family is specifically responsible for hydrolyzing cAMP and plays a vital role in regulating the balance of second messengers. As a crucial regulator in signal transduction, PDE4 has displayed promising pharmacological targets in a variety of diseases, for which its inhibitors have been used as a therapeutic strategy. This review provides a comprehensive summary of the development of PDE4 inhibitors in the past few years, along with the structure, clinical and research progress of multiple inhibitors of PDE4, focusing on the research and development strategies of PDE4 inhibitors. We hope our analysis will provide a significant reference for the future development of new PDE4 inhibitors.

Design, Synthesis and Biological Evaluation of Syn and Anti-like Double Warhead Quinolinones Bearing Dihydroxy Naphthalene Moiety as Epidermal Growth Factor Receptor Inhibitors with Potential Apoptotic Antiproliferative Action

Our investigation includes the synthesis of new naphthalene-bis-triazole-bis-quinolin-2(1H)-ones 4a−e and 7a−e via Cu-catalyzed [3 + 2] cycloadditions of 4-azidoquinolin-2(1H)-ones 3a−e with 1,5-/or 1,8-bis(prop-2-yn-1-yloxy)naphthalene (2) or (6). All structures of the obtained products have been confirmed with different spectroscopic analyses. Additionally, a mild and versatile method based on copper-catalyzed [3 + 2] cycloaddition (Meldal−Sharpless reaction) was developed to tether quinolinones to O-atoms of 1,5- or 1,8-dinaphthols. The triazolo linkers could be considered as anti and syn products, which are interesting precursors for functionalized epidermal growth factor receptor (EGFR) inhibitors with potential apoptotic antiproliferative action. The antiproliferative activities of the 4a−e and 7a−e were evaluated. Compounds 4a−e and 7a−e demonstrated strong antiproliferative activity against the four tested cancer cell lines, with mean GI50 ranging from 34 nM to 134 nM compared to the reference erlotinib, which had a GI50 of 33 nM. The most potent derivatives as antiproliferative agents, compounds 4a, 4b, and 7d, were investigated for their efficacy as EGFR inhibitors, with IC50 values ranging from 64 nM to 97 nM. Compounds 4a, 4b, and 7d demonstrated potent apoptotic effects via their effects on caspases 3, 8, 9, Cytochrome C, Bax, and Bcl2. Finally, docking studies show the relevance of the free amino group of the quinoline moiety for antiproliferative action via hydrogen bond formation with essential amino acids.

Promising heterocycle-based scaffolds in recent (2019-2021) anti-Alzheimer's drug design and discovery

Alzheimer's disease (AD) is one of the neurodegenerative diseases that led to morbidity and mortality world-wide. It is a complex disease whose etiology is not completely known that leads to difficulty in prevent or cure of the AD. Also, there are only few approved drugs for AD treatment. Apart from deaths due to AD, expenditure of treatment and care of AD patients is higher than that of treatment of HIV and cancer diseases combined. Hence, it leads to an economic burden also. Although research is being carried out on designing drugs for AD, most of them have ended up in poor inhibitors with high toxicity. Hence, researchers should shoulder a great responsibility of discovery of efficient drugs for AD treatment. In the field of drug discovery, heterocycles played an important role. Also, most of the heterocyclic scaffolds have been used in design of potent anti-AD agents. In view of this, heterocyclic molecules reported recently are compiled and evaluated comprehensively. Especially, the molecules which exhibited pronounced activity are emphasized and described with respect to structure-activity relationship (SAR) in brief.

Thiazolidinone-linked1,2,3-triazoles with monoterpenic skeleton as new potential anticancer agents: Design, synthesis and molecular docking studies

A novel series of 1,2,3-triazole-thiazolidinone-carvone hybrid compounds has been designed and synthesized using the copper-catalyzed Huisgen azide-alkyne 1,3-dipolar cycloaddition (CuAAC) process based on (R)-Carvone-O-propargylated 5-hydroxybenzylidene-thiazolidin-4-one derivative as starting material. All compounds were characterized and identified based on their NMR and HRMS spectroscopic data. HMBC correlations confirm that under the CuAAC reaction conditions, only the 1,4-disubstituted triazole regioisomers were formed. The targeted 1,2,3-triazole-thiazolidinone-carvone hybrids and their precursors were evaluated for their cytotoxic activity against four human cancer cell lines, including fibrosarcoma (HT-1080), lung carcinoma (A-549), and breast carcinoma (MCF-7 and MDA-MB-231). The obtained data showed that most of these compounds have moderate anti-proliferative activity with IC₅₀ values between 15.04 ± 0.71 and 42.22 ± 1.20 µM. The mechanism of action of the most active compounds 14e and 14f suggested that they induce apoptosis through caspase-3/7 activation, and the compound 14e elicited S-phase arrest, while compound 14f evoked G2/M phase blockade. The molecular docking confirmed that compounds 14e and 14f were nicely bonded with caspace-3 leading up to stable protein-ligand complexes.

Synthesis and bioactivity of phenyl substituted furan and oxazole carboxylic acid derivatives as potential PDE4 inhibitors

In this present study, a series of 5-phenyl-2-furan and 4-phenyl-2-oxazole derivatives were designed and synthesized as phosphodiesterase type 4 (PDE4) inhibitors. In vitro results showed that the synthesized compounds exhibited considerable inhibitory activity against PDE4B and blockade of LPS-induced TNF-α release. Among the designed compounds, Compound 5j exhibited lower IC₅₀ value (1.4 μM) against PDE4 than parent rolipram (2.0 μM) in in vitro enzyme assay, which also displayed good in vivo activity in animal models of asthma/COPD and sepsis induced by LPS. Docking results suggested that introduction of methoxy group at para-position of phenyl ring, demonstrated good interaction with metal binding pocket domain of PDE4B, which was helpful to enhance inhibitory activity.

Retracted Article: Metal-free [2+2+1] cycloaddition polymerization of alkynes, nitriles, and oxygen atoms to functional polyoxazoles

The metal-free [2+2+1] cycloaddition polymerization of alkynes, nitriles, and O-atoms for the regioselective assembly of highly substituted oxazole compounds has been achieved by the use of iodosobenzene (PhIO) with trifluoromethanesulfonic acid (TfOH). The present reaction could be applied to a facile synthesis of polyoxazoles. In this work, the cycloaddition polymerization of 4-cyano-4'-ethynylbiphenyl and PhIO was developed and modified polyoxazole was prepared. All experimental conditions such as polymerization solvent, temperature, catalyst and time were systematically studied. The structure of the obtained polyoxazole was characterized by GPC and NMR, and its thermal properties were studied by TGA. In addition, the good thermal stability of polyoxazoles with unreacted terminal alkynes and cyano groups makes them potentially useful for modifying resins.

Synthesis, Molecular Docking Analysis, and Carbonic Anhydrase Inhibitory Evaluations of Benzenesulfonamide Derivatives Containing Thiazolidinone

To find novel human carbonic anhydrase (hCA) inhibitors, we synthesized thirteen compounds by combining thiazolidinone with benzenesulfonamide. The result of the X-ray single-crystal diffraction experiment confirmed the configuration of this class of compounds. The enzyme inhibition assays against hCA II and IX showed desirable potency profiles, as effective as the positive controls. The docking studies revealed that compounds (2) and (7) efficiently bound in the active site cavity of hCA IX by forming sufficient interactions with active site residues. The fragment of thiazolidinone played an important role in the binding of the molecules to the active site.

Tetrahydroquinoline and tetrahydroisoquinoline derivatives as potential selective PDE4B inhibitors

Tetrahydroquinoline and tetrahydroisoquinoline derivatives containing 2-phenyl-5-furan moiety were designed and synthesized as phosphodiesterase type 4 (PDE4) inhibitors. The bioassay results showed that title compounds showed good inhibitory activity against PDE4B and blockade of LPS (lipopolysaccharide) induced TNF-α release, which also exhibited considerable in vivo activity in animal models of asthma/COPD (chronic obstructive pulmonary disease) and sepsis induced by LPS. The bioactivity of compounds containing tetrahydroquinoline (series 4) was higher than that of tetrahydroisoquinoline derivatives (series 3). Compound 4 m with 4-methoxybenzene moiety exhibited the best potential selective activity against PDE4B. The primary structure-activity relationship study and docking results showed that the tetrahydroquinoline moiety of compound 4 m played a key role to form hydrogen bonds and π-π stacking interaction with PDE4B protein while the rest part of the molecule extended into the catalytic domain to block the access of cAMP and formed the foundation for inhibition of PDE4B. Based on LPS induced sepsis model for the measurement of TNF-α inhibition in Swiss Albino mice and neutrophilia inhibition for asthma and COPD in Sprague Dawley rats with the potential molecules, compound 4 m would be great promise as a hit inhibitor in the future study.

Synthesis and bioactivity of 3,5-dimethylpyrazole derivatives as potential PDE4 inhibitors

A series of 3,5-dimethylpyrazole derivatives containing 5-phenyl-2-furan moiety were designed and synthesized as phosphodiesterase type 4 (PDE4) inhibitors. Bioassay results showed that the title compounds exhibited considerable inhibitory activity against PDE4B and blockade of LPS-induced TNFα release. Among the designed compounds, compound If showed the best inhibitory activity against PDE4B with the IC₅₀ value of 1.7 μM, which also showed good in vivo activity in animal models of asthma/COPD and sepsis induced by LPS. The primary structure-activity relationship (SAR) study and docking results suggested that introduction of the substituent groups to the phenyl ring at the para-position, especially methoxy group, was helpful to enhance inhibitory activity against PDE4B.

Design, synthesis and biological evaluation of novel pyridine-thiazolidinone derivatives as anticancer agents: Targeting human carbonic anhydrase IX

In order to obtain novel Human carbonic anhydrase IX (CAIX) inhibitors, a series of pyridine-thiazolidinone derivatives was synthesized and characterized by various spectroscopic techniques. The binding affinity of the compounds was measured by fluorescence binding studies and enzyme inhibition activity using esterase assay of CAIX. It was observed that compound 8 and 11 significantly inhibit the CAIX activity with the IC₅₀ value, 1.61 μM and 1.84 μM, respectively. The binding-affinity of compound 8 and 11 for CAIX was significantly high with their K_D values 11.21 μM and 2.32 μM, respectively. Docking studies revealed that compound 8 and 11 efficiently binds in the active site cavity of CA IX by forming sufficient numbers of H-bonds and van der Waals interactions with active side residues. All the compounds were further screened in vitro for anticancer activity and found that compound 8 and 11 exhibit considerable anticancer activity against MCF-7 and HepG-2 cell lines. All these findings suggest that compound 8 and 11 may be further exploited as a novel pharmacophore model for the development of anticancer agents.