Benzopyrone, a privileged scaffold in drug discovery: An overview of FDA-approved drugs and clinical candidates

Natural products have always served as an important source of drugs for treating various diseases. Among various privileged natural product scaffolds, the benzopyrone class of compounds has a substantial presence among biologically active compounds. One of the pioneering anticoagulant drugs, warfarin approved in 1954 bears a benzo-α-pyrone (coumarin) nucleus. The widely investigated psoriasis drugs, methoxsalen, and trioxsalen, also contain a benzo-α-pyrone nucleus. Benzo-γ-pyrone (chromone) containing drugs, cromoglic acid, and pranlukast were approved as treatments for asthma in 1982 and 2007, respectively. Numerous other small molecules with a benzopyrone core are under clinical investigation. The present review discusses the discovery, absorption, distribution, metabolism, excretion properties, and synthetic approaches for the Food and Drug Administration-approved and clinical-stage benzopyrone class of compounds. The role of the pyrone core in biological activity has also been discussed. The present review unravels the potential of benzopyrone core in medicinal chemistry and drug development.

Bioisoteres for carboxylic acids: From ionized isosteres to novel unionized replacements

Carboxylic acids are key pharmacophoric elements in many molecules. They can be seen as a problem by some, due to perceived permeability challenges, potential for high plasma protein binding and the risk of forming reactive metabolites due to acyl-glucuronidation. By others they are viewed more favorably as they can decrease lipophilicity by adding an ionizable center which can be beneficial for solubility, and can add enthalpic interactions with the target protein. However, there are many instances where the replacement of a carboxylic acid with a bioisosteric group is required. This has led to the development of a number of ionizable groups which sufficiently mimic the carboxylic acid functionality whilst improving, for example, the metabolic profile of the molecule in question. An alternative strategy involves replacement of the carboxylate by neutral functional groups. This review initially details carefully selected examples whereby tetrazoles, acyl sulfonamides or isoxazolols have been beneficially utilized as carboxylic acid bioisosteres altering physicohemical properties, interactions with the target and metabolism and/or pharmacokinetics, before delving further into the binding mode of carboxylic acid derivatives with their target proteins. This analysis highlights new ways to consider the replacement of carboxylic acids by neutral bioisosteric groups which either rely on hydrogen bonds or cation-π interactions. It should serve as a useful guide for scientists working in drug discovery.

Identification and characterization of forced degradation products of 5-hydroxymethyl-2-furaldehyde (5-HMF) by HPLC, LC-LTQ/Orbitrap and NMR studies

5-Hydroxymethyl-2-furaldehyde (5-HMF) is a kind of aldehyde compound with highly active furan ring, which is generated by dehydration of glucose, fructose, and other monosaccharides. It widely exists in drugs, foods, health products, cosmetics, and traditional Chinese medicine preparations with high sugar content. Due to the toxicity, the concentration of 5-HMF was always monitored to identify non-conformities and adulteration, as well as ensure the process efficiency, traceability and safety in foods or drugs in the pharmacopoeias of various countries. Herein, a comprehensive forced degradation study was performed to characterize the degradation products (DPs) of 5-HMF under hydrolytic (neutral, acidic, and alkaline) degradation, oxidative, thermal, humidity, and photolytic degradation conditions. A total of five degradants were identified, and two of them (DP-3 and DP-5) were novel DPs first reported in our study. Major DPs (i.e., DP-1 and DP-2) with relatively high peak areas were isolated using semi-preparative HPLC and characterized by LC-LTQ/Orbitrap and NMR. 5-HMF was only stable in alkaline hydrolysis condition. In addition, the degradation pathways and mechanism of these DPs were also explained using LC-LTQ/Orbitrap. In silico toxicity and metabolism behavior of the DPs were evaluated using Derek Nexus and Meteor Nexus software, respectively. The predicted toxicity data indicated that both the drug 5-HMF and its DPs bear the potential of hepatotoxicity, mutagenicity, chromosome damage, and skin sensitisation. Our research may be beneficial for the quality control and suitable storage conditions of 5-HMF.

Isolation, Characterization, and Toxicity Study of Stress Degradation Products of Pranlukast Hydrate

Pranlukast hydrate (PRN), a cysteinyl leukotriene receptor antagonist (CysLT₁), is used to treat bronchial asthma. The objective of this study is to perform the isolation, characterization, and toxicity analysis of stress degradation products of PRN. In high-performance liquid chromatography (HPLC), the separation was achieved using a Phenomenex Gemini C18 (250 × 4.6 mm, 5 μ) column; the ammonium format buffer (50 mM), pH 4, with formic acid: acetonitrile (50:50, v/v) was used as a mobile phase at a flow rate of 1.25 mL/min; and the photodiode array detector was used for detection at 230 nm. The drug was subjected to stress degradation as per ICH Q1A (R2) and ICH Q1B guidelines. The drug was found to be labile in alkaline (62.48% degradation) and photolytic (liquid state) (7.67% degradation) conditions, whereas the drug was found to be stable in acidic, peroxide, photolytic (solid state), and thermal conditions. The characterization of the drug and its degradation products was achieved using liquid chromatography-electrospray ionization-quadrupole time of flight tandem mass spectrometry (LC-ESI-QTOF-MS/MS), and the degradation mechanism was proposed. There were two degradation products observed in alkaline conditions (DP6 and DP9), whereas six novel degradation products were observed in photolytic degradation products (DP1, DP3, DP4, DP5, DP7, and DP10). The developed method was successfully validated as per the ICH Q2 (R1) guideline. The isolation of the alkaline degradation product DP9 was performed using preparative HPLC, and it was found to be 96.8% pure degradation product. The characterizations of the isolated degradation product (DP9) and procured impurity were performed using MS/MS, NMR, and FTIR. The mass of the procured impurity and DP9 were observed to be 404 and 500 Da, respectively. The in vitro cytotoxicity study of the procured impurity and DP9 was conducted using a 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay using an A549 cell line, and they were found to be cytotoxic at concentrations above 62.5 and 250 μg/mL, respectively. Furthermore, an in silico toxicity study was performed to predict the toxicity of all the major characterized degradation products of PRN using admetSAR software version 2.0. DP1, DP2, DP6, and DP10 were found to be hepatotoxic, mutagenic according to the micronucleus test, and aquatic toxic. We can conclude that the drug should be kept away from the direct exposure of light and the toxicity levels of DP1, DP2, DP6, and DP10 should be reduced below 0.1% to avoid their toxic effect.

Chromone as a Privileged Scaffold in Drug Discovery: Recent Advances

The use of privileged structures in drug discovery has proven to be an effective strategy, allowing the generation of innovative hits/leads and successful optimization processes. Chromone is recognized as a privileged structure and a useful template for the design of novel compounds with potential pharmacological interest, particularly in the field of neurodegenerative, inflammatory, and infectious diseases as well as diabetes and cancer. This perspective provides the reader with an update of an earlier article entitled "Chromone: A Valid Scaffold in Medicinal Chemistry" ( Chem. Rev. 2014 , 114 , 4960 - 4992 ) and is mainly focused on chromones of biological interest, including those isolated from natural sources. Moreover, as drug repurposing is becoming an attractive drug discovery approach, recent repurposing studies of chromone-based drugs are also reported.