Aryl Substitution Research Articles

Enantioselective Synthesis of α‐Aryl Ketones by a Cobalt‐Catalyzed Semipinacol Rearrangement

AbstractA highly enantioselective cobalt‐catalyzed semipinacol rearrangement of symmetric α,α‐diarylallylic alcohols is disclosed. A chiral cobalt‐salen catalyst generates a highly electrophilic carbocation surrogate following hydrogen atom transfer and radical–polar crossover steps. This methodology provides access to enantioenriched α‐aryl ketones through invertive displacement of a cobalt(IV) complex during 1,2‐aryl migration. A combination of readily available reagents, silane and N‐fluoropyridinium oxidant, are used to confer this type of reactivity. An exploration into the effect of aryl substitution revealed the reaction tolerates para‐ and meta‐halogenated, mildly electron‐rich and electron‐poor aromatic rings with excellent enantioselectivities and yields. The yield of the rearrangement diminished with highly electron‐rich aryl rings whereas very electron‐deficient and ortho‐substituted arenes led to poor enantiocontrol. A Hammett analysis demonstrated the migratory preference for electron‐rich aromatic rings, which is consistent with the intermediacy of a phenonium cation.

Enantioselective Synthesis of α-Aryl Ketones by a Cobalt-Catalyzed Semipinacol Rearrangement.

A highly enantioselective cobalt-catalyzed semipinacol rearrangement of symmetric α,α-diarylallylic alcohols is disclosed. A chiral cobalt-salen catalyst generates a highly electrophilic carbocation surrogate following hydrogen atom transfer and radical-polar crossover steps. This methodology provides access to enantioenriched α-aryl ketones through invertive displacement of a cobalt(IV) complex during 1,2-aryl migration. A combination of readily available reagents, silane and N-fluoropyridinium oxidant, are used to confer this type of reactivity. An exploration into the effect of aryl substitution revealed the reaction tolerates para- and meta-halogenated, mildly electron-rich and electron-poor aromatic rings with excellent enantioselectivities and yields. The yield of the rearrangement diminished with highly electron-rich aryl rings whereas very electron-deficient and ortho-substituted arenes led to poor enantiocontrol. A Hammett analysis demonstrated the migratory preference for electron-rich aromatic rings, which is consistent with the intermediacy of a phenonium cation.

Isothiourea‐Catalysed Acylative Kinetic Resolution of Tertiary Pyrazolone Alcohols

AbstractThe development of methods for the selective acylative kinetic resolution (KR) of tertiary alcohols is a recognised synthetic challenge with relatively few successful substrate classes reported to date. In this manuscript, a highly enantioselective isothiourea‐catalysed acylative KR of tertiary pyrazolone alcohols is reported. The scope and limitations of this methodology have been developed, with high selectivity observed across a broad range of substrate derivatives incorporating varying substitution at N(2)‐, C(4)‐ and C(5)‐, as well as bicyclic constraints within the pyrazolone scaffold (30 examples, selectivity factors (s) typically >100) at generally low catalyst loadings (1 mol %). The application of this KR method to tertiary alcohols derived directly from a natural product (geraniol), alongside pharmaceutically relevant drug compounds (indomethacin, gemfibrozil and probenecid), with high efficiency (s >100) is also described. The KR process is readily amenable to scale up using bench grade solvents and reagents, with effective resolution on a 50 g (0.22 mol) scale demonstrated. The key structural motif leading to excellent selectivity in this KR process has been probed through computation, with an NC=O⋅⋅⋅isothiouronium interaction from substrate to acylated catalyst observed within the favoured transition state. Similarly, the effect of C(5)‐aryl substitution that leads to reduced experimental selectivity is probed, with a competitive π–isothiouronium interaction identified as leading to reduced selectivity.

Isothiourea-Catalysed Acylative Kinetic Resolution of Tertiary Pyrazolone Alcohols.

The development of methods for the selective acylative kinetic resolution (KR) of tertiary alcohols is a recognised synthetic challenge with relatively few successful substrate classes reported to date. In this manuscript, a highly enantioselective isothiourea-catalysed acylative KR of tertiary pyrazolone alcohols is reported. The scope and limitations of this methodology have been developed, with high selectivity observed across a broad range of substrate derivatives incorporating varying substitution at N(2)-, C(4)- and C(5)-, as well as bicyclic constraints within the pyrazolone scaffold (30 examples, selectivity factors (s) typically >100) at generally low catalyst loadings (1 mol%). The application of this KR method to tertiary alcohols derived from a natural product (geraniol), alongside pharmaceutically relevant drug compounds (indomethacin, gemfibrozil and probenecid), with high efficiency (s > 100) is also described. The KR process is readily amenable to scale up, with effective resolution on a 50 g (0.22 mol) scale demonstrated. The key structural motif leading to excellent selectivity in this KR process has been probed through computation, with an NC=O•••isothiouronium interaction observed within the favoured transition state. Similarly, the effect of C(5)-aryl substitution that leads to reduced experimental selectivity is probed, with a competitive π-isothiouronium interaction identified as leading to reduced selectivity.

Medium-Ring Keto Bislactams with Antischistosomal Activity.

We discovered medium-ring keto bislactams as a new antischistosomal chemotype. The ketone functional group and isoindolinone substructure were required for high antischistosomal activity. Aryl substitution with EWG functional groups decreased the chemical stability. These compounds were relatively polar with the measured LogD7.4 values ranging from <0 to 2.4, had kinetic aqueous solubilities between 40 and >320 μM, and had relatively low cytotoxicities with IC50s ranging from 52 to >390 μM. We identified two compounds with IC50 values < 5 μM against ex vivoSchistosoma mansoni (S. mansoni).

Efficient Synthesis of Dithieno[3,2‐B:2’,3’‐d]Thiophenes Derivatives with Promising Optoelectronic Properties Via a One‐Pot, Two‐Step Method with Elemental Sulfur

AbstractDithieno[3,2‐b:2’,3’‐d]thiophene (DTT) derivative contains three annulated thiophene rings, which have attracted great attention in the field of materials due to its planar and conjugated molecular, structural rigidity, and increased solubility. Herein, the one‐step modular construction of a series of structurally well‐defined 2,6‐disubstituted dithieno[3,2‐b:2’,3’‐d]thiophenes (2,6‐DTT) involves Pd/Cu(I)‐catalyzed Sonogashira coupling and LiNH2‐mediated ring‐closing reaction with element sulfur was reported. The method allows the selective and straightforward introduction of different aryl substitution into DTT without otherwise tedious separation and purification processes. The preliminary study of the thermal and photophysical properties demonstrated that the introduction of substituent in phenyl has great impact for the parent molecule, which enable this protocol to synthesis high‐performance 2,6‐DTT through the different alkynes.

Achieving 19.5% Efficiency via Modulating Electronic Properties of Peripheral Aryl-Substituted Small-Molecule Acceptors.

The advancement of acceptors plays a pivotal role in determining photovoltaic performance. While previous efforts have focused on optimizing acceptor-donor-acceptor1-donor-acceptor (A-DA1-D-A)-typed acceptors by adjusting side chains, end groups, and conjugated extension of the electron-deficient central A1 unit, the systematic exploration of the impact of peripheral aryl substitutions, particularly with different electron groups, on the A1 unit and its influence on device performance is still lacking. In this study, three novel acceptors - QxTh, QxPh, and QxPy - with distinct substitutions on the quinoxaline (Qx) are designed and synthesized. Density functional theory (DFT) analyses reveal that QxPh, featuring a phenyl-substituted Qx, exhibits the smallest molecular binding energies and a tightest π···π stacking distance. Consequently, the PM6:QxPh device demonstrates a better power conversion efficiency (PCE) of 17.1% compared to the blends incorporating QxTh (16.4%) and QxPy (15.7%). This enhancement is primarily attributed to suppressed charge recombination, improved charge extraction, and more favorable molecular stacking and morphology. Importantly, introducing QxPh as a guest acceptor into the PM6:BTP-eC9 binary system yields an outstanding PCE of 19.5%, indicating the substantial potential of QxPh in advancing ternary device performance. The work provides deep insights into the expansion of high-performance organic photovoltaic materials through peripheral aryl substitution strategy.

Synthesis, anti-diabetic profiling and molecular docking studies of 2-(2-arylidenehydrazinyl)thiazol-4(5H)-ones.

Aim: To synthesize novel more potent anti-diabetic agents. Methodology: A simple cost effective Hantzsch's synthetic strategy was used to synthesize 2-(2-arylidenehydrazinyl)thiazol-4(5H)-ones. Results: Fifteen new 2-(2-arylidenehydrazinyl)thiazol-4(5H)-ones were established to check their anti-diabetic potential. From alpha(α)-amylase inhibition, anti-glycation and anti-oxidant activities it is revealed that most of the compounds possess good anti-diabetic potential. All tested compounds were found to be more potent anti-diabetic agents via anti-glycation mode. The results of α-amylase and anti-oxidantinhibitionrevealed that compounds are less active against α-amylase and anti-oxidant assays. Conclusion: This study concludes that introduction of various electron withdrawing groups at the aryl ring and substitution of different functionalities around thiazolone nucleus could help to find out better anti-diabetic drug.

Structure-Photoreactivity Studies of BODIPY Photocages: Limitations of the Activation Barrier for Optimizing Photoreactions.

BODIPY photocages are photoreactive chromophores that release covalently linked cargo upon absorption of visible light. Here, we used computations of the T1 photoheterolysis barrier to ascertain whether a computational approach could assist in a priori structure design by identifying new structures with higher quantum yields of photorelease. The electronic structure-photoreactivity relationships were elucidated for boron-substituted and core-functionalized 2-substituted BODIPY photocages as well as aryl substitutions at the meso-methyl position. Although there is a clear trend for the 2-substituted derivatives, with donor-substituted derivatives featuring both lower computed barriers and higher experimental quantum yields, no trend in the quantum yield with the computed activation barrier is found for the meso-methyl-substituted or boron-substituted derivatives. The lack of a correlation between the experimental quantum yield with the computed barrier in the latter two substitution cases is attributed to the substituents having larger effects on the rates of competing channels (internal conversion and competitive photoreactions) than on the rate of the photoheterolysis channel. Thus, although in some cases computed photoreaction barriers can aid in identifying structures with higher quantum yields, the ignored impacts of how changing the structure affects the rates of competing photophysical/photochemical channels limit the effectiveness of this single-parameter approach.

Receptor-based pharmacophore modeling, molecular docking, synthesis and biological evaluation of novel VEGFR-2, FGFR-1, and BRAF multi-kinase inhibitors

A receptor-based pharmacophore model describing the binding features required for the multi-kinase inhibition of the target kinases (VEGFR-2, FGFR-1, and BRAF) were constructed and validated. It showed a good overall quality in discriminating between the active and the inactive in a compiled test set compounds with F1 score of 0.502 and Mathew’s correlation coefficient of 0.513. It described the ligand binding to the hinge region Cys or Ala, the glutamate residue of the Glu-Lys αC helix conserved pair, the DFG motif Asp at the activation loop, and the allosteric back pocket next to the ATP binding site. Moreover, excluded volumes were used to define the steric extent of the binding sites. The application of the developed pharmacophore model in virtual screening of an in-house scaffold dataset resulted in the identification of a benzimidazole-based scaffold as a promising hit within the dataset. Compounds 8a-u were designed through structural optimization of the hit benzimidazole-based scaffold through (un)substituted aryl substitution on 2 and 5 positions of the benzimidazole ring. Molecular docking simulations and ADME properties predictions confirmed the promising characteristics of the designed compounds in terms of binding affinity and pharmacokinetic properties, respectively. The designed compounds 8a-u were synthesized, and they demonstrated moderate to potent VEGFR-2 inhibitory activity at 10 µM. Compound 8u exhibited a potent inhibitory activity against the target kinases (VEGFR-2, FGFR-1, and BRAF) with IC50 values of 0.93, 3.74, 0.25 µM, respectively. The benzimidazole derivatives 8a-u were all selected by the NCI (USA) to conduct their anti-proliferation screening. Compounds 8a and 8d resulted in a potent mean growth inhibition % (GI%) of 97.73% and 92.51%, respectively. Whereas compounds 8h, 8j, 8k, 8o, 8q, 8r, and 8u showed a mean GI% > 100% (lethal effect). The most potent compounds on the NCI panel of 60 different cancer cell lines were progressed further to NCI five-dose testing. The benzimidazole derivatives 8a, 8d, 8h, 8j, 8k, 8o, 8q, 8r and 8u exhibited potent anticancer activity on the tested cell lines reaching sub-micromolar range. Moreover, 8u was found to induce cell cycle arrest of MCF-7 cell line at the G2/M phase and accumulating cells at the sub-G1 phase as a result of cell apoptosis.

O,S-Chelated bis(pentafluorophenyl)boron and diphenylboron-β-thioketonates: synthesis, photophysical, electrochemical and NLO properties.

Boron-β-diketonates are classical emissive materials that have been utilized in various fields, however, boron monothio-β-thioketonates, where one oxygen atom is exchanged for a sulphur atom, have not been explored in detail. To gain a better understanding of this class of materials, we synthesised various aryl substituted monothio-β-diketonate boron complexes with two different aryl substitutions on the boron center and studied their structural, optical and electrochemical properties. Single crystal X-ray analysis revealed that there is considerable deviation in B-O and B-S bond lengths for bis(pentafluorophenyl)boron complexes against diphenyl boron complexes. The bis(pentafluorophenyl)boron complexes have a relatively high absorption coefficient over diphenyl boron complexes. More importantly, a striking difference was observed for the emission behaviour of these compounds. The bis(pentafluorophenyl)boron complexes exhibit weak emission in the solution as well as in the solid state, whereas diphenyl boron complexes do not show any emission in either solution or the solid state. Further, the electrochemical study reveals that diphenyl boron complexes show a reduction potential that is more negative compared to the bis(pentafluorophenyl)boron complexes. The high absorption coefficient of the compounds pointed towards the possibility of high first order hyperpolarizability upon optical excitation, which motivated us to ascertain the nonlinear optical coefficients in the near infrared range, towards applicability of such compounds in optical limiting and switching. The open aperture Z-scan measurements at ultrashort time scales elucidated a few critical features of such compounds towards optical limiting applications.

Aryl-Modified Pentamethyl Cyanine Dyes at the C2' Position: A Tunable Platform for Activatable Photosensitizers.

Pentamethyl cyanine dyes are promising fluorophores for fluorescence sensing and imaging. However, advanced biomedical applications require enhanced control of their excited-state properties. Herein, a synthetic approach for attaching aryl substituents at the C2' position of the thio-pentamethine cyanine (TCy5) dye structure is reported for the first time. C2'-aryl substitution enables the regulation of both the twisted intramolecular charge transfer (TICT) and photoinduced electron transfer (PET) mechanisms to be regulated in the excited state. Modulation of these mechanisms allows the design of a nitroreductase-activatable TCy5 fluorophore for hypoxic tumor photodynamic therapy and fluorescence imaging. These C2'-aryl TCy5 dyes provide a tunable platform for engineering cyanine dyes tailored to sophisticated biological applications, such as photodynamic therapy.

Calcium-Catalyzed Synthesis of Fused Furo[2,3-b]furans and Substituted Furans from 2-Oxo Aldehydes and Cyclic Enols.

We report here an atom-economical, syn-diastereoselective synthesis of naphtho-fused furo[2,3-b]furans along with naphthofurans at room temperature using readily available 2-naphthols and 2-oxo aldehydes using an alkaline earth catalyst [Ca(OTf)2]. 2-Oxo aldehydes having both aryl and alkyl substitutions reacted well. A good number of arenols responded to give fused furans, but selected arenols gave only furofurans. Synthetic applications and gram-scale synthesis were also demonstrated to strengthen this strategy.

Effect of various aryl substitutions on the interfacial interaction energy of graphene/conductive polymer nanocomposites

Studying intermolecular interactions in polymer nanocomposites is highly effective in achieving high-efficiency nanocomposites. To investigate the polymer nanocomposites including conductive polymers, namely poly (3-phenylhydrazone thiophene) (PPHT), poly (3-(4-n-octyl)-phenylthiophene) (POPT), and functionalized graphene nanosheet (FGN), reactive molecular dynamics (RMD) simulation were employed. The FGN structures were a result of the arylation of graphene nanosheets containing different substitutions including sulfide, amine, di-amine, and thiol functional groups. According to interaction energies at polymers / arylated graphene nanosheet, the most interaction energies resulted in nanocomposites of PPHT/graphene-thiophenyl amine (G-PATP) and POPT/graphene-p-Phenylenediamine (G-PPD). Due to the polarity of PPHT, the formation of hydrogen bonding (H-bonding) was expected at specific sites, which were confirmed based on H-bonding interaction criteria. In reality, the criteria required for detecting H-bonding through RDF and the relevant angle measurement have been established. On the other hand, due to the acidic-sensitive hydrazone bond in PPHT, it was expected that the increasing trend in interaction energy of nanocomposites of PPHT could be solely justified based on the acidity of the functional groups employed. However, based on the obtained results, other factors such as the topological polar surface area (TPSA) and the formation of unconventional H-bonding, in addition to the acidity of functional groups, have been considered as influential factors in the changing of interaction energy. Also, the dynamic behavior of polymers was examined by plotting the radius of the gyration (Rg) parameter via time and functional groups. Finally, the temperature effect on interaction energy was determined, too.

Development of QTMP: A promising anticancer agent through NP-Privileged Motif-Driven structural modulation

In this study of creating new molecules from clinical trial agents, an approach of Combretastatin structural modulation with the installation of NP-privileged motifs was considered, and a series of trimethoxyphenyl-2-aminoimidazole with functionalized quinolines and isoquinolines was investigated. An exciting method of quinoline C3-H iodination coupled with imidazopyridine-C3-H arylation and hydrazine-mediated fused-ring cleavage enabled synthesizing a class of compounds with two specific unsymmetric aryl substitutions. Interestingly, three compounds (6, 11, and 13) strongly inhibited HeLa cell proliferation with a half-maximal inhibitory concentration (10–46 nM). Among the compounds, compound 6 (QTMP) showed stronger antiproliferative ability than CA-4 (a clinical trial agent) in various cancer cell lines, including cervical, lung, breast, highly metastatic breast, and melanoma cells. QTMP inhibited the assembly of purified tubulin, depolymerized microtubules of A549 lung carcinoma cells, produced defective spindles, and arrested the cells in the G2/M phase. Further, QTMP binds to the colchicine site in tubulin with a dissociation constant of 5.0 ± 0.6 µM. QTMP displayed higher aqueous stability than CA-4 at 37 °C. Further, in silico analysis of QTMP indicated excellent drug-like properties, including good aqueous solubility, balanced hydrophilicity-lipophilicity, and high GI-absorption ability. The results together suggest that QTMP has anticancer potential.

Novel quinazolinone derivatives as anticancer agents: Design, synthesis, biological evaluation and computational studies

A novel series of quinazoline-pyrimidine derivatives (3a-3i) linked to different aryl substitutions were designed and synthesized as promising anti-cancer candidates. The Chemical structures of the new compounds were confirmed by IR, 1HNMR, 13CNMR, and Mass spectroscopy. Antiproliferative activities of all synthesized compounds were evaluated against MCF-7 and SW480 cell lines by the MTT method. The biological results exhibited IC50 values in the range of 1.1 to 59.0 μM. Compounds 3d and 3f were found to be the most active compounds against the SW480 cell line, with IC50 = 1.1 and 8 μM respectively. Furthermore, in silico analyses of the Absorption, Distribution, Metabolism, Excretion, and Toxicity (ADMET) profiles of the synthesized compounds exhibited that our molecules have acceptable predictive ADMET features. The results of the docking studies were in line with biological outputs, Density functional theory (DFT) studied 3a and 3d's reactivity descriptors at the B3LYP/6-31G** level of theory. HOMO, LUMO, and electrostatic surface potential energy were also examined. According to DFT calculations, compound 3d exhibits higher reactivity than compound 3a, which is consistent with the experimental observations. Molecular dynamic simulation of the potent synthetic compound (3d) and native ligand (Erlotinib) was performed to validate the docking study and also, RMSD, RMSF, total hydrogen bond, and clusters were analyzed.

Synthesis and Cap-Dependent Endonuclease Inhibition of Baloxavir Derivatives

Baloxavir marboxil is a creative antiviral drug for influenza A and B viruses with a novel mechanism of action. In this study, three series comprising a total of 21 previously unreported target compounds were designed and synthesized. The drug-likeness of these compounds was evaluated by molecular docking, PAINS-Remover and SwissADME. The inhibitory effect and affinity of the compounds on the cap-dependent endonuclease activity of the influenza virus were evaluated. Compounds I-4, II-1~II-9 and compound III-8 showed similar inhibitory activity to baloxavir (7.45 μM) on the cap-dependent endonuclease. In particular, compounds I-4 (3.29 μM) and II-2 (1.46 μM) showed strong cap-dependent endonuclease inhibitory activity. The structure–activity relationship studies showed that the inhibitive effect of the compounds on endonuclease was enhanced when the dibenzothiepin rings were substituted by diphenylmethyl containing chiral-center electron-withdrawing groups, dibenzocycloheptane, dihydrodibenzo[b,e]oxepin, and five-member heterocycles containing aryl substitution.

Mechanofluorochromic behaviours of functionalized carbazole-based difluoroboron compounds with different aryl substituents moieties.

To better understand the relationship between molecular structure and mechanofluorochromic characteristics, three carbazole-based N^O-chelated difluoroboron compounds (Cz-S-BF2 , Cz-PhNp-S-BF2 , and Cz-BNp-S-BF2 ) with different aryl substituents moieties were designed and synthesized. The mechanofluorochromic behaviours of Cz-S-BF2 (luminescence from bluish-green to yellowish-green, emission from 504 to 535 nm) without aryl substitution and Cz-PhNp-S-BF2 (luminescence from green and yellow, emission from 521 to 557 nm) with a phenyl-naphthalene group underwent reversible conversion using the grinding-fuming process. For Cz-BNp-S-BF2 this was not apparent due to the well coplanarity of the binaphthalene moiety. Mechanofluorochromic properties were demonstrated through XRD patterns measurement. We envisage that this study will provide a practicable reference to acquire organic molecules with mechanofluorochromic characteristics.

Synthesis and spectral properties of symmetrically arylated BODIPY dyes: Experimental and computational approach

In this study, a series of symmetrically arylated BODIPY dyes were synthesized using a pre-functionalization method, and their structures were characterized by several spectroscopic methods. The relationship between the aryl substitution pattern and the photophysical and electrochemical properties of the dyes was investigated using experimental and computational methods. It was found that electron-donating π-conjugated groups at the meso position and electron-accepting π-conjugated groups at the C3/C5 position led to blue-shifted spectra, while the opposite substitution pattern resulted in red-shifted spectra. Additionally, inductive electron-donating alkyl groups at the meso position produced a blue spectral shift and an alkyl group at the meso position significantly increased the fluorescence quantum yield compared to the arylated counterparts. Computational investigations revealed that a thioanisyl group at the C3/C5 position resulted in a significantly narrow band gap. These results provide valuable insights into the design and development of new BODIPY dyes with tailored properties for various applications.

N-Iodosuccinimide-mediated dimerization and macrocyclization of indodicarbocyanine dyes

The reaction of indodicarbocyanine dyes with N-iodosuccinimide produces dimeric molecules together with the corresponding meso-iodinated dyes depending on the aryl substitution of the dyes and reaction conditions. Iodinated dyes are more reactive in BF3-catalized dimerization than brominated analogues. Reaction of N-iodosuccinimide with N,N′-connected dimeric pentamethines gave rise to macrocyclic dyes with 16- and 20-membered cycles.