Synthesis and biological evaluation of phenolic 4,5-dihydroisoxazoles and 3-hydroxy ketones as estrogen receptor α and β agonists

Exploring the impact of trifluoromethyl (-CF3) functional group on the anti-cancer activity of isoxazole-based molecules: design, synthesis, biological evaluation and molecular docking analysis

Herein we report the design and synthesis of a series of fully-substituted 4-(trifluoromethyl)isoxazoles and evaluation of their anti-cancer activities against MCF-7, 4T1 and PC-3 cell lines as a proof of concept study. 4-(Trifluoromethyl)isoxazole is a synthetically challenging class of molecules and very few synthetic methods have been developed so far and all of them suffered from several serious limitations. Recently we developed a novel, metal-free, and general synthetic strategy to access synthetically challenging 4-(trifluoromethyl)isoxazoles starting from readily available chalcones using cheap CF3SO2Na as the source of the -CF3 group and multitasking t BuONO as an oxidant as well as the source of N and O and thus we have overcome the limitations of the previous methods. Based on the structure of an isoxazole-based anti-cancer agent, 3-(3,4-dimethoxyphenyl)-5-(thiophen-2-yl)isoxazole 14, we designed a set of 4-(trifluoromethyl)isoxazoles for synthesis and further anti-cancer evaluation. Among various molecules, 3-(3,4-dimethoxyphenyl)-5-(thiophen-2-yl)-4-(trifluoromethyl)isoxazole 2g (IC50 = 2.63 μM) and 3-(thiophen-2-yl)-5-(4-(thiophen-2-yl)-1H-pyrrol-3-yl)-4-(trifluoromethyl)isoxazole 5 (IC50 = 3.09 μM) exhibited the best anti-cancer activity against the human breast cancer cell-lines (MCF-7), 2g being the lead molecule among all. Interestingly, 2g is found to be almost 8 times more active compared to its non-trifluoromethylated analogue, i.e., 3-(3,4-dimethoxyphenyl)-5-(thiophen-2-yl)isoxazole 14 (IC50 = 19.72 μM) which revealed the importance of a 'CF3' moiety in enhancing the anti-cancer activity of 14. Further studies such as apoptosis induction, cell cycle analysis, and nuclear staining revealed an apoptotic cell death mechanism. The in silico molecular docking, induced fit analysis, and ADME studies further supported the effect of a -CF3 moiety on the enhancement of anti-cancer activity of isoxazole-based anti-cancer molecules. Further exploration of the biodistribution and therapeutic efficacy of lead 2gin vivo holds significant promise, positioning it as a potential candidate for anticancer therapy.

Pro-aromatic Dihydroquinazolinones - From Multigram Synthesis to Reagents for Gram-scale Metallaphotoredox Reactions

Dihydroquinazolinone (DHQZ) has recently been harnessed as a ketone-derived pro-aromatic reagent extensively employed in (metalla)photoredox reactions as versatile group transfer agents. In this work, we outline a column chromatography-free protocol for the multigram-scale synthesis of pro-aromatic DHQZs as well as its use in a gram-scale nickel/photoredox dual-catalyzed cross-coupling in single-batch, photoflow, and simultaneous multiple smaller batches. While the single-batch approach leveraged moderate yields, a simple plug-flow photoreactor also exhibited amenable productivity (up to 45 % yield) despite the use of a heterogeneous base. Meanwhile, performing the metallaphotoredox-catalyzed reaction in multiple smaller batches in an improvised photoreactor facilitated high yields of up to 59 % and good reproducibility, implying a convenient alternative in the absence of photoflow setups.

O-H bond activation of β,γ-unsaturated oximes via hydrogen atom transfer (HAT) and photoredox dual catalysis

Hydrogen atom transfer (HAT) and photoredox dual catalysis provides a unique opportunity in organic synthesis, enabling the direct activation of C/Si/S-H bonds. However, the activation of O-H bonds of β,γ-unsaturated oximes poses a challenge due to their relatively high redox potential, which exceeds the oxidizing capacity of most currently developed photocatalysts. We here demonstrate that the combination of HAT and photoredox catalysis allows the activation of O-H bond of β,γ-unsaturated oximes. The strategy effectively addresses the oxime's high redox potential and offers a universal pathway for iminoxyl radical formation. Leveraging the versatility of this approach, a diverse array of valuable heterocycles have been synthesized with the use of different radical acceptors. Mechanistic studies confirm a HAT process for the O-H bond activation.

Ti-Catalyzed Modular Ketone Synthesis from Carboxylic Derivatives and gem-Dihaloalkanes

Ketones are ubiquitous in organic synthesis. However, the general method to convert widely available carboxylic acids, unactivated esters, and amides into ketones remains elusive. Herein, we describe the Ti-catalyzed modular ketone synthesis from carboxylic derivatives and easily accessed gem-dihaloalkanes. Notably, this protocol could achieve the direct catalytic olefination of carboxylic acids. This method features a sequence of olefination and electrophilic transformation and good functional group compatibility and allows rapid access to various functionalized ketones. Preliminary mechanistic studies provide insights into the reaction pathway and support the intermediacy of plausible alkylidene titanocene and gem-bimetallic complexes.

Novel N-Acyl Hydrazone Compounds as Promising Anticancer Agents: Synthesis and Molecular Docking Studies

In this study, a new series of N-acyl hydrazones 7a-e, 8a-e, and 9a-e, starting from methyl δ-oxo pentanoate with different substituted groups 1a-e, were synthesized as anticancer agents. The structures of obtained target molecules were identified by spectrometric analysis methods (FT-IR, ¹¹H NMR, ¹³C NMR, and LC-MS). The antiproliferative activity of the novel N-acyl hydrazones was evaluated on the breast (MCF-7) and prostate (PC-3) cancer cell lines by an MTT assay. Additionally, breast epithelial cells (ME-16C) were used as reference normal cells. All newly synthesized compounds 7a-e, 8a-e, and 9a-e exhibited selective antiproliferative activity with high toxicity to both cancer cells simultaneously without any toxicity to normal cells. Among these novel N-acyl hydrazones, 7a-e showed the most potent anticancer activities with IC₅₀ values at 7.52 ± 0.32-25.41 ± 0.82 and 10.19 ± 0.52-57.33 ± 0.92 μM against MCF-7 and PC-3 cells, respectively. Also, molecular docking studies were applied to comprehend potential molecular interactions between compounds and target proteins. It was seen that the docking calculations and the experimental data are in good agreement.

Pd-Catalysed [3 + 2]-cycloaddition towards the generation of bioactive bis-heterocycles/identification of COX-2 inhibitors via in silico analysis

In the current research, we envisaged the synthesis of bis-heterocycles containing the dihydroisoxazole ring by [3 + 2] cycloaddition of VECs (vinyl ethylene carbonates) and nitrile oxides, assisted by a Pd catalyst. Herein we explored hydroximoyl chlorides as versatile precursors for the in situ generation of nitrile oxides that were exploited to achieve the cycloaddition reaction on a vinyl group of VECs to generate bis-heterocycles. In silico-based studies of bis-heterocycles on the cyclooxygenase (COX) enzyme displayed selective COX-2 inhibition.

BF3·OEt2-mediated cyclization of β,γ-unsaturated oximes and hydrazones with N-(arylthio/arylseleno)succinimides: an efficient approach to synthesize isoxazoles or dihydropyrazoles

A highly efficient BF3·OEt2-mediated cyclization of β,γ-unsaturated oximes and tosylhydrazones with N-(arylthio/arylseleno)succinimides has been established for the construction of N-heterocycles in a one-step manner. This metal-free cyclization provides direct access to isoxazoles and dihydropyrazoles in good to excellent yields at room temperature. The mechanistic experiments support the formation of a cationic species PhS+ which plays a critical role in this cyclization process.

Metal-free oxysulfonylation and aminosulfonylation of alkenyl oximes: synthesis of sulfonylated isoxazolines and cyclic nitrones

Intramolecular oxysulfonylation of alkenyl oximes was reported. Using iodine as the catalyst, TBHP as the oxidant, and sulfonyl hydrazides as the sulfonyl radical source, a variety of sulfonylated isoxazolines were obtained in moderate to excellent yields. Cyclic nitrones could also be readily obtained under the same conditions.

Hypervalent iodine-mediated Ritter-type amidation of terminal alkenes: The synthesis of isoxazoline and pyrazoline cores

Hypervalent iodine-mediated olefin functionalization provides a rapid gateway towards accessing both various heterocyclic cores and functional groups. In this regard, we have developed a Ritter-type alkene functionalization utilizing a PhI(OAc)₂ ((diacetoxyiodo)benzene, PIDA)/Lewis acid combination in order to access isoxazoline and pyrazoline cores. Based on allyl ketone oximes and allyl ketone tosylhydrazones, we have developed an alkene oxyamidation and amido-amidation protocol en route to accessing both isoxazoline and pyrazoline cores. Additionally, acetonitrile serves as both the solvent and an amine source in the presence of this PIDA/Lewis acid combination. This operationally straightforward and metal-free protocol provides an easy access to isoxazoline and pyrazoline derivatives.

Iodine(iii)-mediated intramolecular sulfeno- and selenofunctionalization of β,γ-unsaturated tosyl hydrazones and oximes

A cascade radical cyclization/sulfenylation or selenylation of β,γ-unsaturated hydrazones and oximes was realized under mild conditions with phenyliodine(iii) diacetate (PIDA) as the sole oxidant, leading to the construction of diversely functionalized heteroatom-containing pyrazoline and isoxazoline derivatives.

Copper-mediated oxysulfonylation of alkenyl oximes with sodium sulfinates: a facile synthesis of isoxazolines featuring a sulfone substituent

A novel and efficient Cu(OAc)₂-mediated oxysulfonylation of alkenyl oximes with sodium sulfonates was developed. The reactions are easy to conduct, occur under mild conditions, and form a broad range of sulfone-substituted isoxazolines in good yields.

Discovery of Novel Selective ERα/ERβ Ligands by Multi-pharmacophore Modeling and Virtual Screening

Estrogen receptor α (ERα) and estrogen receptor β (ERβ) regulate different sets of gene expression, and have different ligand responses, which make the estrogen tissue-specific. Thus, the estrogen receptor (ER) subtype-selective ligands can improve the target-site selectivity and decrease the off-target effect. In order to discover the selective ER subtype ligands with novel scaffolds, in this work three-dimensional (3D) pharmacophore models of the ERα ligands (Hypo 1) and the ERβ ligands (Hypo 2) were established (correlation coefficients were 0.959 and 0.966) and validated (R=0.936 and 0.879; enrichment factors (EFs) at 2% were 16.2 and 8.4; areas under the concentration-time curve (AUC) of the receiver operating curve (ROC) were 0.88 and 0.91) using the Discovery Studio 4.0 software package. Hypo 1 and Hypo 2 were then employed for virtual screening and ten hits were found as potential candidate leads. Based on their ERα/ERβ binding affinity results by fluorescence polarization technology, two of these leads, AH-262/34334025 (AH) and AG-670/08803023 (AG) with novel scaffolds were identified as selective ERα ligands. A molecular docking study was also performed, which provided the explanation for the ER subtype preferences for AH and AG.

Substituent effect study on experimental ¹³C NMR chemical shifts of (3-(substituted phenyl)-cis-4,5-dihydroisoxazole-4,5-diyl)bis(methylene)diacetate derivatives

Eleven novel (3-(substituted phenyl)-cis-4,5-dihydroisoxazole-4,5-diyl)bis(methylene) diacetate derivatives were synthesized in the present study. These dihydroisoxazole derivatives were characterized by IR, (1)H NMR, (13)C NMR and elemental analyses. Their (13)C NMR spectra were measured in Deuterochloroform (CDCl3). The correlation analysis for the substituent-induced chemical shift (SCS) with Hammett substituent constant (σ), inductive substituent constant (σI), different of resonance substituent constants (σR, σR(o)) and Swain-Lupton substituent parameters (F, R) were performed using SSP (single substituent parameter), and DSP (dual substituent parameter) methods, as well as single and multiple regression analysis. From the result of regression analysis, the effect of substituent on the (13)C NMR chemical shifts was explained.

Catalytic Enantioselective 1,4-Iodofunctionalizations of Conjugated Dienes

The first catalytic enantioselective 1,4-iodofunctionalizations of conjugated dienes have been developed. Starting from β,γ,δ,ε-unsaturated oximes and 4-Ns hydrazones, these N-iodosuccinimide-mediated reactions are catalyzed by newly modified tertiary aminothiourea derivatives and furnish Δ(2)-isoxazoline and Δ(2)-pyrazoline derivatives, respectively, containing an (E)-allyl iodide group at the quaternary stereogenic center generally in high yield and with excellent enantioselectivity (up to 98.5:1.5 er).

Iodine(III)-Mediated Oxy-fluorination of Alkenyl Oximes: An Easy Path to Monofluoromethyl-Substituted Isoxazolines

A highly regioselective intramolecular oxy-fluorination of alkenyl oximes was achieved. This new transformation represents an efficient method for the preparation of monofluoromethyl-substituted isoxazolines. The synthetic application of the oxy-fluorination product was demonstrated by a one-step synthesis of monofluoromethyl-substituted β-hydroxyl ketone derivatives.

Copper-catalyzed intramolecular oxytrifluoromethylthiolation of unactivated alkenes

A mild, versatile, and convenient method for efficient intramolecular oxytrifluoromethylthiolation of unactivated alkenes catalyzed by Cu(OAc)2 has been developed. The reactions were carried out under aerobic conditions and formed a variety of isoxazolines bearing a -SCF3 substituent.

Estrogen receptor ligands: a patent review update

INTRODUCTION

The role of estrogens is mostly mediated by two nuclear receptors (ERα and ERβ) and a membrane-associated G-protein (GPR30 or GPER), and it is not limited to reproduction, but it extends to the skeletal, cardiovascular and central nervous systems. Various pathologies such as cancer, inflammatory, neurodegenerative and metabolic diseases are often associated with dysfunctions of the estrogenic system. Therapeutic interventions by agents that affect the estrogenic signaling pathway might be useful in the treatment of many dissimilar diseases.

AREAS COVERED

The massive chemodiversity of ER ligands, limited to patented small molecules, is herein reviewed. The reported compounds are classified on the basis of their chemical structures. Non-steroidal derivatives, which mostly consist of diphenolic compounds, are further segregated into chemical classes based on their central scaffold.

EXPERT OPINION

Estrogens have been used for almost a century and their earlier applications have concerned interventions in the female reproductive functions, as well as the treatment of some estrogen-dependent cancers and osteoporosis. Since the discovery of ERβ in 1996, the patent literature has started to pay a progressively increasing attention to this newer receptor subtype, which holds promise as a target for new indications, most of which still need to be clinically validated.