Privileged Structures Research Articles

Synthesis, crystal structure, structural and spectroscopic analysis of (2E)-1-(4-chlorophenyl)-3-(4-methoxyphenyl)prop-2-en-1-one

Chalcones are privileged structures in chemistry because they present a variety of possibilities for the construction of new molecules, which can be obtained from natural sources or by synthesis. In the solid-state, chalcones can crystalize into various space groups, and their molecular arrangements are directly associated with their chemical and physical properties. The aim of the present work was to investigate the structural, vibrational, electronic and non-linear optical (NLO) properties of a novel chalcone crystal (2E)-1-(4-chlorophenyl)-3-(4-methoxyphenyl)prop‑2-en-1-one (C16H13ClO3, hereafter named CLPMP). This chalcone was synthesized and characterized by single-crystal X-ray Diffraction (XRD), Fourier Transform Raman (FT-Raman), Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR), and Ultraviolet-visible (UV–Vis) spectroscopy. The thermal stability of CLPMP was also evaluated by thermogravimetric analysis (TGA) and differential thermogravimetric (DTG). Theoretical quantum chemistry calculations were performed to obtain information about their chemical and physical properties. Our crystallographic data show that at room temperature, CLPMP has a monoclinic structure with P21/c space group, and four molecules per unit cell, with the following cell lengths: a = 15.5924 (4) Å, b = 14.5537 (4) Å, c = 5.90980 (10) Å, and β = 90.046(2)°. A comparison between the experimental and theoretical Raman spectra allowed us to assign all normal modes of this crystal. Through the experimental and theoretical UV absorption spectra of chalcone CLPMP, it was possible to identify the electronic transitions of its first six singlet states. From the Hirshfeld surfaces analysis it was verified that short intermolecular contacts are responsible for stabilizing the packing of the CLPMP crystal. Our NLO study and thermal analysis showed that the chalcone CLPMP can be a good material for optical applications.

Benzimidazole: A Promising target for the development of novel drug molecules against breast cancer

Breast cancer is considered as one of the deadliest diseases dominantly in developed and developing countries. Continuous research is required in order to design and develop better therapeutic agents for cancer treatment with more selectivity, efficacy and reduced toxicity. Fused heterocyclic ring system has been identified as a privileged structure by several researchers that can be used as a template for drug discovery and development in Medicinal Chemistry. Wide range of drugs with therapeutic potential contain hetero-aromatic bicyclic ring system as pharmacophore. According to various research outputs in the literature substituted benzimidazoles have wide range of pharmacological profiles with multi-targeting ability, making them an important basic nucleus for the design and development of novel therapeutic agents for the treatment of complex cancers including breast cancer, skin cancer, and blood cancer. In the presented article we have discussed research outputs by many scientists in the last few years that support the candidature of benzimidazole scaffold for the development of novel therapeutic agents against breast cancer along with their mechanism of action. This review also focuses on little introductory idea about benzimidazole nucleus and types of breast cancer.

Diarylether‐Amino Acid Conjugates as New Class of Anticancer Agents

AbstractDiarylether (DE) is a privileged structure found in both natural products and synthetic compounds including small molecule drugs. We present the synthesis of a series of 13 new DE‐amino acid conjugates which were screened for cancer cells antiproliferation activity. Structure‐activity relationship suggests ester and phenyl groups in DE‐Phe‐OEt 4 c are important for the activity. Compound 4 c inhibited strongly MCF‐7 3D tumor sphere formation and have favourable calculated physical chemical properties according to Lipinski's rule of 5. Docking study suggests estrogen receptor and/ or 3a‐HSD type 3 protein could be the target(s) for anticancer activity of this class of compounds.

Synthesis, Biological, Spectroscopic and Computational Investigations of Novel N-Acylhydrazone Derivatives of Pyrrolo[3,4-d]pyridazinone as Dual COX/LOX Inhibitors.

Secure and efficient treatment of diverse pain and inflammatory disorders is continually challenging. Although NSAIDs and other painkillers are well-known and commonly available, they are sometimes insufficient and can cause dangerous adverse effects. As yet reported, derivatives of pyrrolo[3,4-d]pyridazinone are potent COX-2 inhibitors with a COX-2/COX-1 selectivity index better than meloxicam. Considering that N-acylhydrazone (NAH) moiety is a privileged structure occurring in many promising drug candidates, we decided to introduce this pharmacophore into new series of pyrrolo[3,4-d]pyridazinone derivatives. The current paper presents the synthesis and in vitro, spectroscopic, and in silico studies evaluating the biological and physicochemical properties of NAH derivatives of pyrrolo[3,4-d]pyridazinone. Novel compounds 5a-c-7a-c were received with high purity and good yields and did not show cytotoxicity in the MTT assay. Their COX-1, COX-2, and 15-LOX inhibitory activities were estimated using enzymatic tests and molecular docking studies. The title N-acylhydrazones appeared to be promising dual COX/LOX inhibitors. Moreover, spectroscopic and computational methods revealed that new compounds form stable complexes with the most abundant plasma proteins-AAG and HSA, but do not destabilize their secondary structure. Additionally, predicted pharmacokinetic and drug-likeness properties of investigated molecules suggest their potentially good membrane permeability and satisfactory bioavailability.

Design, synthesis and biological evaluation of a novel bioactive indane scaffold 2-(diphenylmethylene)c-2,3-dihydro-1H-inden-1-one with potential anticancer activity

Over the past decades, designing of privileged structures has emerged as a useful approach to the discovery and optimisation of novel biologically active molecules, and many have been successfully exploited across and within different target families. Examples include indole, quinolone, isoquinoline, benzofuran and chromone, etc. In the current study, we focus on synthesising a novel hybrid scaffold constituting naturally occurring benzophenone (14) and indanone (22) ring systems, leading to a general structure of 2-(diphenylmethylene)-2,3-dihydro-1H-inden-1-one (23). It was hypothesised this new hybrid system would provide enhanced anti-cancer activity owing to the presence of the common features associated with the tubulin binding small molecule indanocine (10) and the estrogen receptor (ER) antagonist tamoxifen (24). Key hybrid molecules were successfully synthesised and characterised, and the in vitro cytotoxicity assays were performed against cancer cell lines: MCF7 (breast) and SKBR3 (breast), DU145 (prostate) and A549 (lung). The methyl-, chloro- and methoxy-, para-substituted benzophenone hybrids displayed the greatest degree of cytotoxicity and the E-configuration derivatives 45, 47 and 49 being significantly most potent. We further verified that the second benzyl moiety of this novel hybrid scaffold is fundamental to enhance the cytotoxicity, especially in the SKBR3 (HER2+) by the E-methyl lead molecule 47, MCF7 (ER+) by 45 and 49, and A549 (NSCLC) cell lines by 49. These hybrid molecules also showed a significant accumulation of SKBR3 cells at S-phase of the cell cycle after 72 hrs, which demonstrates besides of being cytotoxic in vitro against SKBR3 cells, 47 disturbs the replication and development of this type of cancer causing a dose-dependent cell cycle arrest at S-phase. Our results suggest that DNA damage might be involved in the induction of SKBR3 cell death caused by the hybrid molecules, and therefore, this novel system may be an effective suppressor of HER2+/Neu-driven cancer growth and progression. The present study points to potential structural optimisation of the series and encourages further focussed investigation of analogues of this scaffold series toward their applications in cancer chemoprevention or chemotherapy.

Visible-Light Photoswitchable Benzimidazole Azo-Arenes as β-Arrestin2-Biased Selective Cannabinoid 2 Receptor Agonists.

The cannabinoid 2 receptor (CB2 R) has high therapeutic potential for multiple pathogenic processes, such as neuroinflammation. Pathway-selective ligands are needed to overcome the lack of clinical success and to elucidate correlations between pathways and their respective therapeutic effects. Herein, we report the design and synthesis of a photoswitchable scaffold based on the privileged structure of benzimidazole and its application as a functionally selective CB2 R "efficacy-switch". Benzimidazole azo-arenes offer huge potential for the broad extension of photopharmacology to a wide range of optically addressable biological targets. We used this scaffold to develop compound 10 d, a "trans-on" agonist, which serves as a molecular probe to study the β-arrestin2 (βarr2) pathway at CB2 R. βΑrr2 bias was observed in CB2 R internalization and βarr2 recruitment, while no activation occurred when looking at Gα16 or mini-Gαi . Overall, compound 10 d is the first light-dependent functionally selective agonist to investigate the complex mechanisms of CB2 R-βarr2 dependent endocytosis.

Indol-3-ylglyoxylamide as Privileged Scaffold in Medicinal Chemistry.

In recent years, indolylglyoxylamide-based derivatives have received much attention due to their application in drug design and discovery, leading to the development of a wide array of compounds that have shown a variety of pharmacological activities. Combining the indole nucleus, already validated as a "privileged structure," with the glyoxylamide function allowed for an excellent template to be obtained that is suitable to a great number of structural modifications aimed at permitting interaction with specific molecular targets and producing desirable therapeutic effects. The present review provides insight into how medicinal chemists have elegantly exploited the indolylglyoxylamide moiety to obtain potentially useful drugs, with a particular focus on compounds exhibiting activity in in vivo models or reaching clinical trials. All in all, this information provides exciting new perspectives on existing data that can be useful in further design of indolylglyoxylamide-based molecules with interesting pharmacological profiles. The aim of this report is to present an update of collection data dealing with the employment of this moiety in the rational design of compounds that are able to interact with a specific target, referring to the last 20 years.

Mit sichtbarem Licht schaltbare Benzimidazol‐Azo‐Arene wirken als β‐Arrestin2 funktionell selektive Cannabinoid‐Rezeptor 2 Agonisten

AbstractDer Cannabinoid 2 Rezeptor (CB2R) besitzt großes therapeutisches Potential bei zahlreichen pathophysiologischen Prozessen wie z. B. der Neuroinflammation. Signalweg‐selektive Liganden werden benötigt, um mangelnden klinischen Erfolg zu überwinden und um die Zusammenhänge zwischen einzelnen Signalwegen und deren therapeutischen Effekten zu beleuchten. Hier berichten wir vom Design und der Synthese eines photoschaltbaren chemischen Gerüsts basierend auf der “privilegierten” Struktur des Benzimidazols und seiner Anwendung als funktionell selektiven CB2R “Wirksamkeitsschalter” (”efficacy switch”). Benzimidazol‐Azo‐Arene bieten großes Potential für eine breite Erweiterung der Photopharmakologie auf eine Vielzahl optisch adressierbarer biologischer Zielstrukturen. Wir haben dieses Gerüst verwendet, um Substanz 10 d zu entwickeln, ein “trans‐on” Agonist, der als molekulare Sonde dient, um den β‐Arrestin2 (βArr2) Signalweg am CB2R zu untersuchen. Die selektive Aktivierung des βΑrr2 Signalweges wurde mittels CB2R Internalisierung und βArr2 Rekrutierung nachgewiesen, während keine Aktivierung bei der Betrachtung von Gα16 oder mini‐Gαi auftrat. Insgesamt stellt Substanz 10 d den ersten Licht‐abhängigen funktionell selektiven Agonisten dar, mit dem die komplexen βArr2‐abhängigen Mechanismen der Endozytose am CB2R untersucht werden können.

The Importance of the Pyrazole Scaffold in the Design of Protein Kinases Inhibitors as Targeted Anticancer Therapies.

The altered activation or overexpression of protein kinases (PKs) is a major subject of research in oncology and their inhibition using small molecules, protein kinases inhibitors (PKI) is the best available option for the cure of cancer. The pyrazole ring is extensively employed in the field of medicinal chemistry and drug development strategies, playing a vital role as a fundamental framework in the structure of various PKIs. This scaffold holds major importance and is considered a privileged structure based on its synthetic accessibility, drug-like properties, and its versatile bioisosteric replacement function. It has proven to play a key role in many PKI, such as the inhibitors of Akt, Aurora kinases, MAPK, B-raf, JAK, Bcr-Abl, c-Met, PDGFR, FGFRT, and RET. Of the 74 small molecule PKI approved by the US FDA, 8 contain a pyrazole ring: Avapritinib, Asciminib, Crizotinib, Encorafenib, Erdafitinib, Pralsetinib, Pirtobrutinib, and Ruxolitinib. The focus of this review is on the importance of the unfused pyrazole ring within the clinically tested PKI and on the additional required elements of their chemical structures. Related important pyrazole fused scaffolds like indazole, pyrrolo[1,2-b]pyrazole, pyrazolo[4,3-b]pyridine, pyrazolo[1,5-a]pyrimidine, or pyrazolo[3,4-d]pyrimidine are beyond the subject of this work.

Is It Possible to Obtain a Product of the Desired Configuration from a Single Knoevenagel Condensation? Isomerization vs. Stereodefined Synthesis.

The biological activity of compounds directly depends on the three-dimensional arrangement of affinity fragments since a high degree of pharmacophore compliance with the binding site is required. 3-Benzylidene oxindoles are privileged structures due to their wide spectrum of biological activity, synthetic availability, and ease of modification. In particular, both kinase inhibitors and kinase activators can be found among 3-benzylidene oxindoles. In this work, we studied model compounds obtained via oxindole condensation with aldehydes and alkylphenones. These condensation products can exist in the form of E- and Z-isomers and also undergo isomerization in solutions. The factors causing isomeric transformation of these compounds were established. Comparative kinetic studies to obtain quantitative characteristics of UV-driven isomerization were first performed. The results obtained indicate dramatic differences in two subclasses, which should be considered when developing biologically active molecules.

C-H Glycosylation of Native Carboxylic Acids: Discovery of Antidiabetic SGLT-2 Inhibitors.

C-Glycosides are critical motifs embedded in many bioactive natural products. The inert C-glycosides are privileged structures for developing therapeutic agents owing to their high chemical and metabolic stability. Despite the comprehensive strategies and tactics established in the past few decades, highly efficient C-glycoside syntheses via C-C coupling with excellent regio-, chemo-, and stereoselectivity are still needed. Here, we report the efficient Pd-catalyzed glycosylation of C-H bonds promoted by weak coordination with native carboxylic acids without external directing groups to install various glycals to the structurally diverse aglycon parts. Mechanistic evidence points to the participation of a glycal radical donor in the C-H coupling reaction. The method has been applied to a wide range of substrates (over 60 examples), including many marketed drug molecules. Natural product- or drug-like scaffolds with compelling bioactivities have been constructed using a late-stage diversification strategy. Remarkably, a new potent sodium-glucose cotransporter-2 inhibitor with antidiabetic potential has been discovered, and the pharmacokinetic/pharmacodynamic profiles of drug molecules have been changed using our C-H glycosylation approach. The method developed here provides a powerful tool for efficiently synthesizing C-glycosides to facilitate drug discovery.

Sparteine-Free, Highly Stereoselective Construction of Complex Allylic Alcohols Using 1,2-Metallate Rearrangements.

Stereotriads bearing allylic alcohols are privileged structures in natural products, and new methods accessing these in a stereoselective fashion are highly sought after. Toward this goal, we found that the use of chiral polyketide fragments allows for performing the Hoppe-Matteson-Aggarwal rearrangement in the absence of sparteine with high yields and diastereoselectivities, rendering this protocol a highly valuable alternative to the Nozaki-Hiyama-Takai-Kishi reaction. The switch of directing groups in most cases resulted in the reversed stereochemical outcome, which could be explained by conformational analysis on density functional theory level and a Felkin-like model.

1,3-Thiazole derivatives as privileged structures for anti-Trypanosoma cruzi activity: Rational design, synthesis, in silico and in vitro studies

Chagas disease is a deadly and centenary neglected disease that is recently surging as a potential global threat. Approximately 30% of infected individuals develop chronic Chagas cardiomyopathy and current treatment with the reference benznidazole (BZN) is ineffective for this stage. We presently report the structural planning, synthesis, characterization, molecular docking prediction, cytotoxicity, in vitro bioactivity and mechanistic studies on the anti-T. cruzi activity of a series of 16 novel 1,3-thiazoles (2–17) derived from thiosemicarbazones (1a, 1b) in a two-step and reproducible Hantzsch-based synthesis approach. The anti-T. cruzi activity was evaluated in vitro against the epimastigote, amastigote and trypomastigote forms of the parasite. In the bioactivity assays, all thiazoles were more potent than BZN against epimastigotes. We found that the compounds presented an overall increased anti-tripomastigote selectivity (Cpd 8 was 24-fold more selective) than BZN, and they mostly presented anti-amastigote activity at very low doses (from 3.65 μM, cpd 15). Mechanistic studies on cell death suggested that the series of 1,3-thiazole compounds herein reported cause parasite cell death through apoptosis, but without compromising the mitochondrial membrane potential. In silico prediction of physicochemical properties and pharmacokinetic parameters showed promising drug-like results, being all the reported compounds in compliance with Lipinski and Veber rules. In summary, our work contributes towards a more rational design of potent and selective antitripanosomal drugs, using affordable methodology to yield industrially viable drug candidates.

Design and synthesis of pseudo-rutaecarpines as potent anti-inflammatory agents via regulating MAPK/NF-κB pathways to relieve inflammation-induced acute liver injury in mice

Pseudo-natural products (PNPs) design strategy provides a great valuable entrance to effectively identify of novel bioactive scaffolds. In this report, novel pseudo-rutaecarpines were designed via the combination of several privileged structure units and 46 target compounds were synthesized. Most of them display moderate to potent inhibitory effect on LPS-induced NO production and low cytotoxicity in RAW264.7 macrophage. The results of the anti-inflammatory efficacy and action mechanism of compounds 7l and 8c indicated that they significantly reduced the release of IL-6, IL-1β and TNF-α. Further studies revealed that they can strongly inhibit the activation of NF-κB and MAPK signal pathways. The LPS-induced acute liver injury mice model studies not only confirmed their anti-inflammatory efficacy in vivo but also could effectively relieve the liver injury in mice. The results suggest that compounds 7l and 8c might serve as lead compounds to develop therapeutic drugs for treatment of inflammation.

Rhodium-Catalyzed Isoquinoline Synthesis Using Vinyl Selenone as Oxidizing Acetylene Surrogate

Isoquinoline is a privileged structure in many bioactive compounds and valuable ligands. Transition-metal-catalyzed oxidative annulation of imine derivatives has become a promising synthetic method; however, catalytic synthesis of 3,4-nonsubstituted isoquinolines by formal acetylene annulation has been scarce to date. Herein, we introduce vinyl selenone as an effective acetylene surrogate for the Rh-catalyzed annulative coupling under mild conditions. The Se fragment can be recovered as diselenide and recycled. The product can readily be converted to 1-aminoisoquinolines.

Application and SARs of Pyrazolo[1,5-a]pyrimidine as Antitumor Agents Scaffold.

Pyrazolo[1,5-a]pyrimidines are fused heterocycles that have spawned many biologically active antitumor drugs and are important privileged structures for drug development. Pyrazolo[1,5- a]pyrimidine derivatives have played an important role in the development of antitumor agents due to their structural diversity and good kinase inhibitory activity. In addition to their applications in traditional drug targets such as B-Raf, KDR, Lck, and Src kinase, some small molecule drugs with excellent activity against other kinases (Aurora, Trk, PI3K-γ, FLT-3, C-Met kinases, STING, TRPC) have emerged in recent years. Therefore, based on these antitumor drug targets, small molecule inhibitors containing pyrazolo[1,5-a]pyrimidine scaffold and their structure-activity relationships are summarized and discussed to provide more reference value for the application of this particular structure in antitumor drugs.

Illuminating the Chemical Space of Untargeted Proteins

According to the Illuminating the Druggable Genome (IDG) initiative, 90% of the proteins encoded by the human genome still lack an identified active ligand, that is, a small molecule with biologically relevant binding potency or functional activity in an in vitro assay. Under this scenario, there is an urgent need for new approaches to chemically address these yet untargeted proteins. It is widely recognized that the best starting point for generating novel small molecules for proteins is to exploit the expected polypharmacology of known active ligands across phylogenetically related proteins following the paradigm that similar proteins are likely to interact with similar ligands. Here, we introduce a computational strategy to identify privileged structures that, when chemically expanded, are highly probable to contain active small molecules for untargeted proteins. The protocol was first tested on a set of 576 currently targeted proteins having at least one protein family sibling the year before their first active ligand was reported. A privileged structure contained in active ligands that were identified in the following years was correctly anticipated for 214 (37%) of those targeted proteins, a lower-bound recall estimate when considering data completeness issues. When applied to a set of 1184 untargeted potential druggable genes in cancer, the identification of privileged structures from known bioactive ligands of protein family siblings allowed for extracting a priority list of diverse commercially available small molecules for 960 of them. Assuming a minimum success rate of 37%, the chemical library selections should be able to deliver active ligands for at least 355 currently untargeted proteins associated with cancer.

Rapid and Efficient Access to Novel Bio-Inspired 3-Dimensional Tricyclic SpiroLactams as Privileged Structures via Meyers' Lactamization.

The concept of privileged structure has been used as a fruitful approach for the discovery of novel biologically active molecules. A privileged structure is defined as a semi-rigid scaffold able to display substituents in multiple spatial directions and capable of providing potent and selective ligands for different biological targets through the modification of those substituents. On average, these backbones tend to exhibit improved drug-like properties and therefore represent attractive starting points for hit-to-lead optimization programs. This article promotes the rapid, reliable, and efficient synthesis of novel, highly 3-dimensional, and easily functionalized bio-inspired tricyclic spirolactams, as well as an analysis of their drug-like properties.

Identification of Novel Zika Virus Inhibitors: A Screening using Thiosemicarbazones and Thiazoles Templates.

Zika virus (ZIKV) remains an important cause of congenital infection, fetal microcephaly, and Guillain-Barré syndrome in the population. In 2016, WHO declared a cluster of microcephaly cases and other neurological disorders reported as a global public health emergency in Brazil. There is still no specific treatment for Zika virus fever, only palliative care. Therefore, there is a need for new therapies against this disease. According to the literature, thiosemicarbazone, phthalimide and thiazole are privileged structures with several biological activities, including antiviral activity against various viruses. Based on this, this work presents an antiviral screening using previously synthesized compounds derived from thiosemicarbazone, phthalimide, and thiazole as new hits active against ZIKV. After synthesis and characterization, all compounds were submitted to Cytotoxicity by MTT and Antiviral activity against ZIKV assays. Compounds 63, 64, 65, and 73 exhibited major reductions in the ZIKV title from this evaluation. Compounds 63 (99.74%), 64 (99.77%), 65 (99.92%), and 73 (99.21%) showed a higher inhibition than the standard 6MMPr (98.74%) at the CC20 dose. These results revealed new chemical entities with anti-ZIKV activity. These derivatives are promising candidates for further assays. In addition, the current approach brings a new privileged scaffolding, which may drive future drug discovery for ZIKV.

Triethylammonium 2-(3-Hydroxy-2-oxoindolin-3-yl)-5,5-dimethyl-3-oxocyclohex-1-en-1-olate

In recent years, the application of privileged structures has become a powerful approach in the discovery of new biologically active molecules. Ion pairing is a strategy used to enhance the permeation of ionized topical drugs. A convenient and efficient method for the synthesis of triethylammonium 2-(3-hydroxy-2-oxoindolin-3-yl)-5,5-dimethyl-3-oxocyclohex-1-en-1-olate has been developed. The presented protocol includes an aldol reaction and the formation of an ammonium salt. Triethylamine is both a reactant and a catalyst in the process. The structure of the synthesized title compound has been established by 1H, 13C-NMR and IR spectroscopy, mass spectrometry, and elemental analysis.