Design and synthesis of novel Y-shaped barbituric acid derivatives as PPARγ activators

Practice of green chemistry strategies in synthetic organic chemistry: a glimpse of our sincere efforts in green chemistry research

This feature article summarises our recent contributions (2019-2023) in designing and developing a handful of promising organic transformations for accessing several diversely functionalised biologically relevant organic scaffolds, following the green chemistry principles, particularly focusing on the application of low-energy visible light, electrochemistry, ball-milling, ultrasound, and catalyst- and additive-free synthetic strategies.

Crystal structures of non-uracil ring fragments in complex with Mycobacterium tuberculosis uracil DNA glycosylase (MtUng) as a starting point for novel inhibitor design: A case study with the barbituric acid fragment

Uracil DNA glycosylase (UDG or Ung) is a key enzyme involved in uracil excision from the DNA as a repair mechanism. Designing Ung inhibitors is thus a promising strategy to treat different cancers and infectious diseases. The uracil ring and its derivatives have been shown to inhibit Mycobacterium tuberculosis Ung (MtUng), resulting from specific and strong binding with the uracil-binding pocket (UBP). To design novel MtUng inhibitors, we screened several non-uracil ring fragments hypothesised to occupy MtUng UBP due to their high similarity to the uracil structural motif. These efforts have resulted in the discovery of novel MtUng ring inhibitors. Here we report the co-crystallised poses of these fragments, confirming their binding within the UBP, thus providing a robust structural framework for the design of novel lead compounds. We selected the barbituric acid (BA) ring as a case study for further derivatisation and SAR analysis. The modelling studies predicted the BA ring of the designed analogues to interact with the MtUng UBP much like the uracil ring. The synthesised compounds were screened in vitro using radioactivity and a fluorescence-based assay. These studies led to a novel BA-based MtUng inhibitor 18a (IC₅₀ = 300 μM) displaying ∼24-fold potency over the uracil ring.

Development of Heterocyclic PPAR Ligands for Potential Therapeutic Applications

The family of nuclear peroxisome proliferator-activated receptors (PPARα, PPARβ/δ, and PPARγ) is a set of ligand-activated transcription factors that regulate different functions in the body. Whereas activation of PPARα is known to reduce the levels of circulating triglycerides and regulate energy homeostasis, the activation of PPARγ brings about insulin sensitization and increases the metabolism of glucose. On the other hand, PPARβ when activated increases the metabolism of fatty acids. Further, these PPARs have been claimed to be utilized in various metabolic, neurological, and inflammatory diseases, neurodegenerative disorders, fertility or reproduction, pain, and obesity. A series of different heterocyclic scaffolds have been synthesized and evaluated for their ability to act as PPAR agonists. This review is a compilation of efforts on the part of medicinal chemists around the world to find novel compounds that may act as PPAR ligands along with patents in regards to PPAR ligands. The structure-activity relationship, as well as docking studies, have been documented to better understand the mechanistic investigations of various compounds, which will eventually aid in the design and development of new PPAR ligands. From the results of the structural activity relationship through the pharmacological and in silico evaluation the potency of heterocycles as PPAR ligands can be described in terms of their hydrogen bonding, hydrophobic interactions, and other interactions with PPAR.

Role of Peroxisome Proliferator-Activated Receptor Gamma (PPARγ) in Different Disease States: Recent Updates

Peroxisome proliferator-activated receptor (PPAR), a ligand dependant transcription factor, is a member of the nuclear receptor superfamily. PPAR exists in three isoforms i.e. PPAR alpha (PPARα), PPAR beta (PPARβ), and PPAR gamma (PPARγ). These are multi-functional transcription factors and help in regulating inflammation, type 2 diabetes, lipid concentration in the body, metastasis, and tumor growth or angiogenesis. Activation of PPARγ causes inhibition of growth of cultured human breast, gastric, lung, prostate, and other cancer cells. PPARγ is mainly involved in fatty acid storage, glucose metabolism, and homeostasis and adipogenesis regulation. A large number of natural and synthetic ligands bind to PPARγ and modulate its activity. Ligands such as thiazolidinedione, troglitazone, rosiglitazone, pioglitazone effectively bind to PPARγ; however, most of these were found to display severe side effects such as hepatotoxicity, weight gain, cardiovascular complications and bladder tumor. Now the focus is shifted towards the development of dual-acting or pan PPAR ligands. The current review article describes the functions and role of PPARγ in various disease states. In addition, recently reported PPARγ ligands and pan PPAR ligands were discussed in detail. It is envisaged that the present review article may help in the development of potent PPAR ligands with no or minimal side effects.

Supramolecular assembly and spectroscopic characterization of indolenine–barbituric acid zwitterions

The intermolecular hydrogen bonding of barbiturates assists in the supramolecular aggregation and a hypsochromic shift is shown in protic solvents.

Synthesis of New Pyrimidinone Derivatives and Their Respective Biological Activity Assessment

Barbituric acid is converted into a pyrimidinone-incorporated pyrazolyl moiety (1), which is a key starting material. 1 can be converted into pyrimidine dione, isoxazole, pyrimidopyrimidine, and pyranopyrimidine by reacting with hydrazine hydrate and/or phenyl hydrazine, hydroxyl amine, urea, thiourea, guanidine, ethyl acetoacetate and ethyl cyanoacetate. Acylation of 1 gave an important key intermediate (7), which was condensed to form chalcone, which then underwent cycloaddition into cyclohexenes (8-13). Some newly synthesized compounds were screened as anti-diabetic agents and exhibited significant activity. These freshly manufactured compounds were characterized using different methods. These compounds showed significant activity as anti-diabetic agents, especially compound 4b, with IC50= 13.54 μg/ml, which is very close to that of the standard acarbose (IC50= 12.87 µg/ml). Additionally, these compounds showed cytotoxic inhibition activity against the colon carcinoma (HCT116), hepatocellular carcinoma (HEPG2), and breast carcinoma (MCF7) cells; compounds 11, 4b, and 10 showed the best activity, with IC50 = 19.3, 2.6, and 5 μg/ml, respectively.

Identification and characterization of a sterically robust phenylalanine ammonia-lyase among 481 natural isoforms through association of in silico and in vitro studies

The enzyme phenylalanine ammonia lyase (PAL) is of special importance for the treatment of phenylketonuria patients. The aim of this study was to find a stable recombinant PAL with suitable kinetic properties among all natural PAL producing species using in silico and experimental approaches. To find such a stable PAL among 481 natural isoforms, 48,000 of 3-D models were predicted using the Modeller 9.10 program and evaluated by Ramachandran plot. Correlation analysis between Ramachandran plot and the energy of different thermodynamic components indicated that this plot could be an appropriate tool to predict protein stability. Hence, PAL6 from Lotus japonicus (LjPAL6) was selected as a stable isoform. Molecular dynamic (MD) simulation for 50 ns and docking has been conducted for LjPAL6-phenylalanine complex. The best PAL-phenylalanine frame was selected by re-docking with l-phenylalanine (L-Phe) and root-mean-square deviation (RMSD) value. MD simulation showed that the complex has a good stability, depicted by the low RMSD value, binding free energy and hydrogen bindings. Docking results showed that LjPAL6 has a high affinity toward l-Phe according to the low level of binding free energy. By overexpressing Ljpal6 in E. coli BL21, a total of 33.5 mg/l of protein was obtained, which has been increased to 83.7 mg/l via the optimization of LjPAL6 production using response surface methodology. The optimal pH and temperature were 8.5 and 50 °C, respectively. LjPAL6 showed a specific activity of 42 nkat/mg protein, with K_m, K_cat and K_cat/K_m values of 0.483 mM, 7 S^-1 and 14.5 S^-1 mM^-1 for l-phe, respectively. In conclusion, finding models with the most reasonable stereo-chemical quality and lowest numbers of steric clashes would result in easier folding. Hence, in silico analyses of bulk data from natural origin will lead one to find an optimal model for in vitro studies and drug design.

Hypoglycemic Efficacy of Docking Selected Natural Compounds against α-Glucosidase and α-Amylase

The inhibition of α-glucosidase and α-amylase is a clinical strategy for the treatment of type II diabetes, and herbal medicines have been reported to credibly alleviate hyperglycemia. Our previous study has reported some constituents from plant or herbal sources targeted to α-glucosidase and α-amylase via molecular docking and enzymatic measurement, but the hypoglycemic potencies in cell system and mice have not been validated yet. This study was aimed to elucidate the hypoglycemic efficacy of docking selected compounds in cell assay and oral glucose and starch tolerance tests of mice. All test compounds showed the inhibition of α-glucosidase activity in Caco-2 cells. The decrease of blood sugar levels of test compounds in 30 min and 60 min of mice after OGTT and OSTT, respectively and the decreased glucose levels of test compounds were significantly varied in acarbose. Taken altogether, in vitro and in vivo experiments suggest that selected natural compounds (curcumin, antroquinonol, HCD, docosanol, tetracosanol, rutin, and actinodaphnine) via molecular docking were confirmed as potential candidates of α-glucosidase and α-amylase inhibitors for treating diabetes.

Structural Basis for the Enhanced Anti-Diabetic Efficacy of Lobeglitazone on PPARγ

Peroxisome proliferator-activated receptor γ (PPARγ) is a member of the nuclear receptor superfamily. It functions as a ligand-activated transcription factor and plays important roles in the regulation of adipocyte differentiation, insulin resistance, and inflammation. Here, we report the crystal structures of PPARγ in complex with lobeglitazone, a novel PPARγ agonist, and with rosiglitazone for comparison. The thiazolidinedione (TZD) moiety of lobeglitazone occupies the canonical ligand-binding pocket near the activation function-2 (AF-2) helix (i.e., helix H12) in ligand-binding domain as the TZD moiety of rosiglitazone does. However, the elongated p-methoxyphenol moiety of lobeglitazone interacts with the hydrophobic pocket near the alternate binding site of PPARγ. The extended interaction of lobeglitazone with the hydrophobic pocket enhances its binding affinity and could affect the cyclin-dependent kinase 5 (Cdk5)-mediated phosphorylation of PPARγ at Ser245 (in PPARγ1 numbering; Ser273 in PPARγ2 numbering). Lobeglitazone inhibited the phosphorylation of PPARγ at Ser245 in a dose-dependent manner and exhibited a better inhibitory effect on Ser245 phosphorylation than rosiglitazone did. Our study provides new structural insights into the PPARγ regulation by TZD drugs and could be useful for the discovery of new PPARγ ligands as an anti-diabetic drug, minimizing known side effects.

Design, virtual screening, molecular docking and molecular dynamics studies of novel urushiol derivatives as potential HDAC2 selective inhibitors

Three series of novel urushiol derivatives were designed by introducing a hydroxamic acid moiety into the tail of an alkyl side chain and substituents with differing electronic properties or steric bulk onto the benzene ring and alkyl side chain. The binding affinity toward HDAC2 of the compounds was screened by Glide docking. The best scoring compounds were processed further with molecular docking, MD simulations and binding free energy studies to analyze the binding modes and mechanisms. Six compounds, 21, 23, 10, 19, 9 and 30, gave Glide scores of -7.9 to -8.5, which revealed that introducing F, Cl, triazole, benzamido, formamido, hydroxyl or nitro substituents onto the benzene ring could increase binding affinity significantly. Molecular docking studies revealed that zinc ion coordination, hydrogen bonding and hydrophobic interactions contributed to the high calculated binding affinities of these compounds toward HDAC2 and that His145, His146, Gly154, Glu103, His183, Asp104, Tyr308 and Phe155 contributed favorably to the binding. MD simulations and binding free energy studies showed that all complexes possessed good stability as characterized by low RMSDs; low RMSFs of residues, moderate hydrogen bonding and zinc ion coordination; and low values of binding free energies. van der Waals and electrostatic interactions provided major contributions to the stability of these complexes. These results show the promising potential of urushiol derivatives as potent HDAC2 binding lead compounds.

Multitargeted bioactive ligands for PPARs discovered in the last decade

Type 2 diabetes took insulin resistance as the main clinical manifestation. PPARs have been reported to be the therapeutic targets of metabolic disorders, such as obesity, hypertension, diabetes, and cardiovascular disease. Previously, PPARγ agonist rosiglitazone was restricted in clinic due to cardiomyocytes infarction, weight gain, and other serious side-effects, which were mainly due to the single and selective PPARγ agonism. In recent years, multitarget-directed PPAR agonists with synergistic reaction as well as fewer side-effect have been the hot topic in designing promising agents. In this review, we updated and generalized the development of PPARγ partial agonists, PPARγ antagonists, PPARα/γ dual agonists, PPARδ partial agonists, PPARδ antagonists, PPARα/δ dual agonists, PPARγ/δ dual agonists, and PPARα/γ/δ pan-agonists published in recent decade. Most of these molecules were modified from known structures or came from high-throughput screening. Among these molecules, some were expected to be promising drugs against metabolic disorders, while others seemed to provide new insight for designing novel PPAR agents.