Base-catalyzed Cyclization Research Articles

Synthesis, enzyme inhibitory kinetics, & computational studies of N-(substituted phenyl)-(5-(3,4-dichlorobenzyl)-4-(4-chlorophenyl)-4H-1,2,4-triazol-3-ylthio)methylbenzamides: As potent alkaline phosphatase inhibitors

The present research work encompass an innovative approach towards the synthesis of potent series of target compounds (8a-j) having 1,2,4-triazole and benzamide moieties as alkaline phosphatase inhibitors. The synthetic methodology was initiated by Fischer's esterification of 3,4-dichlorophenylacetic acid (1) to achieve ethyl 2-(3,4-dichlorophenyl)acetate (2) which underwent hydrazinolysis using hydrazine hydrate under reflux to 2-(3,4-dichlorophenyl)acetohydrazide (3). The compound (3) with 4-chlorophenyl isothiocyanate (4) was base-catalyzed cyclization (10% aqueous NaOH) to 4-(4-chlorophenyl)-5-(3,4-dichlorobenzyl)-4H-1,2,4-triazole-3-thiol (5) under reflux via N-(4-chlorophenyl)-2-(2-(3,4-dichlorophenyl)acetyl)hydrazinecarbocarbothioamide, as an intermediate. Finally, a series of derivatives (8a-j) was synthesized by reacting (5) with different electrophiles; N-(aryl)-4-(chloromethyl)benzamides (7a-j) which were obtained by the reaction of substituted aryl amines (6a-j) with 4-(chloromethyl)benzoyl chloride in aqueous alkaline medium. The structural confirmation of all these novel derivatives was corroborated by contemporary spectral analysis i.e., IR, EI-MS, 1H and 13CNMR . The in vitro inhibitory potential of these benzamides against alkaline phosphatase enzyme disclosed that nine out of ten exhibited potent inhibition relative to standard used. Among these, 8i was identified as most potent molecule with IC50 value of (0.046 ± 0.013 μM), comparative to standard (5.241 ± 0.471 μM). The Kinetics mechanism examined by Lineweaver-Burk Plots (LBP), which revealed that 8i inhibited alkaline phosphatase enzyme competitively by forming an enzyme-inhibitor complex. The inhibition constant Ki determined from Dixon plots of this compound was 0.02 µM. The results of computational study were in full agreement with experimental proceedings and these ligands showed good interactions with the active site of enzyme. Based on the current investigations, these potent inhibitotrs might lead to further research gateways for the discovery of non-toxic medicinal scaffolds for dealing with the alkaline phosphatase ailments such as bone diseases and liver dysfunction. DFT analysis was also performed.

Regioselective Synthesis of 2,4- and 2,5-Disubstituted 1,3-Thiazoles from 2-Oxo-2-(amino)ethanedithioates via Base-Catalyzed Cyclization

AbstractFacile and efficient methods are reported for the synthesis of 2,4- and 2,5-disubstituted-1,3-thiazoles by the cyclization of 2-oxo-2-(amino)ethanedithioates with TosMIC and α-haloketones in high yields. Key structures were confirmed based on X-ray crystallographic studies. In addition, investigation of ground state geometry, electronic and molecular structural properties, FMOs, global reactivity descriptors, MEP and NCI analyses were predicted to access the information related to the stability, reactivity, and strength of the interactions present in the molecules by quantum chemical calculations. Further, the potency of derivatives was tested against the SARS-Cov2 receptor (PDB ID: 7mc6) via molecular docking approach with binding scores of –6.0 to –8.4 kcal/mol.

Synthesis of 2-(2-nitrophenyl)indoline-3-acetic acid derivatives via base-catalyzed cyclization of N-(2-nitrobenzyl)-2-aminocinnamic acid derivatives.

A protocol for the synthesis of 2-(2-nitrophenyl)indoline-3-acetic acid derivatives was developed via base-catalyzed cyclization of N-(2-nitrobenzyl)-2-aminocinnamic acid derivatives. The synthetic utility of this methodology was illustrated by the concise synthesis of dihydropaullone, a partially saturated analog of paullone. Furthermore, the indoline scaffold could be further converted to the corresponding indoles and other indole-fused heterocycles.

Regioselective Synthesis of 5- and 3-Hydroxy-N-Aryl-1H-Pyrazole-4-Carboxylates and Their Evaluation as Inhibitors of Plasmodium falciparum Dihydroorotate Dehydrogenase.

In silico evaluation of various regioisomeric 5- and 3-hydroxy-substituted alkyl 1-aryl-1H-pyrazole-4-carboxylates and their acyclic precursors yielded promising results with respect to their binding in the active site of dihydroorotate dehydrogenase of Plasmodium falciparum (PfDHODH). Consequently, four ethyl 1-aryl-5-hydroxy-1H-pyrazole-4-carboxylates and their 3-hydroxy regioisomers were prepared by two-step syntheses via enaminone-type reagents or key intermediates. The synthesis of 5-hydroxy-1H-pyrazoles was carried out using the literature protocol comprising acid-catalyzed transamination of diethyl [(dimethylamino)methylene]malonate with arylhydrazines followed by base-catalyzed cyclization of the intermediate hydrazones. For the synthesis of isomeric methyl 1-aryl-3-hydroxy-1H-pyrazole-4-carboxylates, a novel two-step synthesis was developed. It comprises acylation of hydrazines with methyl malonyl chloride followed by cyclization of the hydrazines with tert-butoxy-bis(dimethylamino)methane. Testing the pyrazole derivatives for the inhibition of PfDHODH showed that 1-(naphthalene-2-yl)-5-hydroxy-1H-pyrazole-4-carboxylate and 1-(naphthalene-2-yl)-, 1-(2,4,6-trichlorophenyl)-, and 1-[4-(trifluoromethyl)phenyl]-3-hydroxy-1H-pyrazole-4-carboxylates (~30% inhibition) were slightly more potent than a known inhibitor, diethyl α-{[(1H-indazol-5-yl)amino]methylidene}malonate (19% inhibition).

Discovery of new pyrimido[5,4-c]quinolines as potential antiproliferative agents with multitarget actions: Rapid synthesis, docking, and ADME studies

A novel series of pyrimido[5,4-c]quinoline derivatives variously substituted at positions 2 and 5 have been synthesized, in good to excellent yields, via rapid base-catalyzed cyclization reaction of 2,4-dichloroquinoline-3-carbonitrile (5) with guanidine hydrochlorides 6a-c. All the synthesized compounds were screened for their in vitro antiproliferative activity. The most active hybrids 26a-d, 28a-d, and 30B were assessed against topoisomerase (topo) I, topo IIα, CDK2, and EGFR. The majority of the tested compounds exhibited selective topo I inhibitory activity while had weak topo IIα inhibitory action with compounds 30B and 28d, showed better topo I inhibitory activity than the reference camptothecin. Compound 30B, the most potent derivative as antiproliferative agent, exhibited moderate activity against CDK2 (IC50 = 1.60 µM). The results of this assay show that CDK2 is not a potential target for these compounds, implying that the observed cytotoxicity of these compounds is due to a different mechanism. Compounds 30B, 28d, and 28c were found to be the most potent against EGFR and their EGFR inhibitory activities (IC50 = 0.40 ± 0.2, 0.49 ± 0.2, and 0.64 ± 0.3, respectively) relative to the positive control erlotinib (IC50 = 0.07 ± 0.03 µM). These results revealed that topo I and EGFR are attractive targets for this class of chemical compounds.

Cyclic Peroxidic Carbon Dioxide Dimer Fuels Peroxyoxalate Chemiluminescence.

Peroxyoxalate chemiluminescence is used in self-contained light sources, such as glow sticks, where oxidation of aromatic oxalate esters produces a high-energy intermediate (HEI) that excites fluorescence dyes via electron transfer chemistry, mimicking bioluminescence for efficient chemical energy-to-light conversion. The identity of the HEI and reasons for the efficiency of the peroxyoxalate reaction remain elusive. We present here unequivocal proof that the HEI of the peroxyoxalate system is a cyclic peroxidic carbon dioxide dimer, namely, 1,2-dioxetanedione. Oxalic peracids bearing a substituted phenyl group were unable to directly excite fluorescent dyes; hence, they could be ruled out as the HEI. However, base-catalyzed cyclization of these species results in bright chemiluminescence, with decay rates and chemiexcitation quantum yields that are influenced by the electronic phenylic substituent properties. Hammett (ρ = +2.2 ± 0.1) and Brønsted (β = -1.1 ± 0.1) constants for the cyclization step preceding chemiexcitation imply that the loss of the phenolate-leaving group and intramolecular nucleophilic attack of the percarboxylate anion occur in a concerted manner, generating 1,2-dioxetanedione as the unique outcome. The presence of better leaving groups influences the reaction mechanism, favoring the chemiluminescent reaction pathway over the nonemissive formation of aryl-1,2-dioxetanones.

Synthesis, Spectral Evaluation and in Silico Studies of S-Aralkylated 5-(4-methoxyphenyl)-4-phenyl-4H-1,2,4-triazole-3-thiols: As suitable Alzheimerand#39;s disease drug candidates

Our efforts lay emphasis on synthesis of S-aralkylated 5-(4-OMeC6H5)-4-phenyl-4H-1,2,4-triazol-3-thiols like pharmacologically active candidates to counter neurodegenerative disorder; Alzheimerand#39;s disease. A synthetic strategy was instigated by esterifying 4-methoxybenzoic acid through Fisher esterificationand#39;s methodology. Hydrazinolysis of corresponding ester was performed under reflux with methanolic hydrated hydrazine to afford 4-methoxybenzohydrazide (I) which refluxing with phenyl isothiocyanate (II) in MeOH to yield a reactive intermediate (III). The later underwent base-catalyzed intermolecular cyclization to furnish 5-(4-OMeC6H5)-4H-1,2,4-triazol-3-thiol (IV). Ultimately, IV was aralkylated at thiol position with aralkyl halides V(a-l) in polar aprotic solvent and catalytic amounts of LiH to provide S-aralkylated 5-(4- OMeC6H5)-4-phenyl-4H-1,2,4-triazol-3-thiols VI(a-l). Modern spectral analysis data explicitly established all the substitutions on nucleophilic S-atom of parent 1,2,4-triazol-3-thiol ring. Effective anti-cholinesterase potential depicted in 3-(phenylpropylthio)-5-(4-OMeC6H5)-4-phenyl-4H-1,2,4-triazole; VIc (IC50; 3.26and#177;0.35 μM) against acetyl cholinesterase; AChE and 3-(phenethylthio)-5-(4-OMeC6H5)-4-phenyl-4H-1,2,4-triazole; VIb (IC50; 8.52and#177;0.54 μM) against butyrylcholinesterase; BChE enzyme as compared to standard Eserine for both enzymes (IC50; 0.04and#177;0.01 μM). Molecular modelling analyses had been conducted to recognize the interconnection of these compounds with enzymes that suggested key interactions (Docking is made to untie the active binding sites). Anti-proliferative activity results showed VIg and VIj with -Cl groups on benzylic ring as promising candidates with HCT-116 cell viability of 14.83 % and 3.09 % respectively.

Synthesis of Natural and Unnatural Quinolones Inhibiting the Growth and Motility of Bacteria.

Synthesis of a recently discovered S-methylated quinolone natural product (1) was carried out, in addition to the production of a range of 2-substituted 4-quinolone derivatives (2-11). Two approaches were used: (i) the base-catalyzed cyclization of N-(ketoaryl)amides; (ii) attachment of the substituent to the quinolone core via a Suzuki-Miyaura cross-coupling. Also produced were a small suite of related 2(1H)-quinolones (12-19). The synthesized compounds were assessed for their antimicrobial properties. The alkene-substituted 4-quinolone 8 significantly inhibited the growth of a Pseudomonas aeruginosa strain, and both 4-quinolones and 2(1H)-quinolones were capable of inhibiting the swarming behavior of Bacillus subtilis.

Synthesis of N-substituted-4-methylene-oxazolidinones via base-catalyzed cyclization of propargylic alcohols with p-toluenesulfonyl isocyanate

A practical method is developed for the synthesis of oxazolidinone derivatives, an important class of heterocyclic compounds. The effect of bases and solvents on this cyclization reaction is discussed and a simple new base–solvent system (triethylamine in toluene) is found to be the most effective. The reaction conditions developed here are mild and no by-products are observed. Moreover, using optimized conditions, a number of differently substituted propargylic alcohols are cyclized to the corresponding N-substituted-4-methylene-oxazolidinones in yields of up to 99%.

Synthesis, inhibition studies against AChE and BChE, drug-like profiling, kinetic analysis and molecular docking studies of N-(4-phenyl-3-aroyl-2(3H)-ylidene) substituted acetamides

Halogenated and non-halogenated N-(4-phenyl-3-aroyl-2(3H)-ylidene) substituted acetamides were prepared by base-catalyzed cyclization of corresponding acetyl thioureas with phenacyl bromide. The synthesized compounds were structurally characterized by 1H NMR and 13C NMR spectroscopy and were screened against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzyme inhibition activities. Molecular docking studies, drug-like profiling and kinetic analysis were performed to further investigate the inhibition mechanism of the compounds. This study provided useful insights into the design and development of novel dual inhibitors, in addition to understanding the mechanism by which such drugs interact with targets and exert their biochemical action. All the compounds showed superior inhibition profile compared to the standards possessing sub-micromolar and micromolar IC50 values for AChE and BChE, respectively. Docking simulations revealed that the compound 6g showed strong binding inside the active site gorges of both AChE and BChE. An excellent agreement was obtained as the best docked poses showed important binding features mostly based on interactions due to aromatic moieties and oxygen atoms of the compound. Cation-pi/pi-pi interactions together with hydrogen bond forces were the key players responsible for ligand anchoring in the active sites. The striking results accomplished both in docking computations and experimental findings ascertained that the compound 6g can serve as a scaffold for both AChE and BChE inhibition.

A General Synthesis of Benzoazepinoindoles – A New Class of Heterocycles

A new class of heterocyclic compounds, namely the benzoazepinoindolones, has been synthesised through a base-catalysed cyclisation reaction of 1,4-bis(2-aminophenyl)-2-phenylbutane-1,4-dione derivatives and features the prominent seven-membered azepine ring moiety. This synthesis has considerable scope for the rapid generation of more complex structures and is inexpensive and generally applicable.

Highly efficient enantioselective synthesis of 1,3-disubstituted 2,5-diketopiperazine derivatives via microwave irradiation

Chiral 2,5-diketopiperazine (2,5-DKP) derivatives have a broad range of biological activities in the medicinal field. The synthetic protocols of 1,3-disubstituted 2,5-DKPs via base-catalyzed cyclization of chloroacetamide have been reported. However, there are several drawbacks, such as an overly long reaction time, low to moderate yield, and racemization of the products. The sequence modified herein of 1,3-disubstituted 2,5-DKPs involves microwave-assisted cyclization. It increases yields and reduces reaction time. Furthermore, employing N-PMB protection prevents racemization, which frequently occurs in the base-catalyzed cyclization reaction. Consequently, the rapid synthetic method of enantiomerically pure 1,3-disubstituted 2,5-DKPs via microwave reaction was established successfully.

A facile method for monitoring solid-phase peptide synthesis and for N-terminal modification of peptides: synthesis of short peptides for imaging specific cells

A simple method for naked-eye detection of free amine groups during solid-phase peptide synthesis is reported. The technique involves base-catalyzed cyclization of 2-(2-oxo-2H-acenaphthylene-1-ylidene)-malononitrile (1) and subsequent oxidative substitution of aryl moiety by free amine group present at the N-terminus of the peptide chain that leads to the formation of a chromophore, which distinguishes the deprotected peptide chain from the protected one. The reaction is fast, does not require heating, and allows N-terminal modification of peptides suitable for imaging specific cells. Base catalyzed cyclization of 2-(2-oxo-2H-acenaphthylene-1-ylidene)-malononitrile and subsequent oxidative substitution by free amine group leads to the formation of a chromophore, which permits naked-eye detection of the deprotected peptide on resin support.

Synthesis of Phostones via the Palladium-Catalyzed Ring Opening of Epoxy Vinyl Phosphonates.

The reaction of epoxy aldehydes with tetraethyl methylenediphosphonate gave γ,δ-epoxy vinyl phosphonates. The palladium-catalyzed addition of primary alcohols gave the monoprotected diols as single diastereoisomers. The trans- and cis-epoxides lead to opposite ( syn and anti) diastereoisomers of the addition products. The alkene of the vinyl phosphonates was subjected to hydrogenation, and the resulting saturated phosphonates underwent base-catalyzed cyclization to give phostones with a very high diastereoselectivity in the formation of the new chiral center at the phosphorus atom.

Efficient synthesis of pyrazolopyridines containing a chromane backbone through domino reaction.

An efficient approach for the synthesis of pyrazolopyridines containing the aminochromane motif through a base-catalyzed cyclization reaction is reported. The synthesis was carried out through a three-component reaction of (arylhydrazono)methyl-4H-chromen-4-one, malononitrile, primary amines in the presence of Et3N at room temperature. However, carrying out the reaction under the same conditions without base led to a fused chromanyl-cyanopyridine. High selectivity, high atom economy, and good to high yields in addition to mild reaction conditions are the advantages of this approach.

Synthetic modification and cytotoxic evaluation of 2-cyano-3,4-secotriterpenic methylketones

Triterpenic methylketones, known earlier and obtainable as a result of oxidative transformation of double bond(s) in 2-cyano-3,4-secoderivatives of the lupane and 18αH-oleanane types, can be regarded as promising intermediates for synthetic transformation. This study has demonstrated the acid-catalyzed α-bromination of methylketones as capable of providing a series of various bromine-substituted ketones with different degrees of halogenation, as well as the 3,23,24-trinor-3,4-seco-18αH-oleanane acid resulting from the tribromoketone by elimination of a bromoform fragment under the same conditions. The 3,4-seco-acid ester derivative was then transformed, via the base-catalyzed intramolecular nitrile anion cyclization, to a derivative with the ketonitrile fragment in the five-membered A cycle, dehydrogenation of which afforded a cyano enone derivative. With use of the base catalysis, the 3,4-secotriterpenic bromohydrins synthesized via stereoselective reduction of 18αH-oleanane mono- and dibromoketones were transformed to C(4) epimeric terminal 4,23-epoxides. According to cytotoxic screening of the synthesized compounds, the bromoketones showed the most pronounced cytotoxic effect, whereas their derivatives partially or completely lost their cytotoxicity against the tumor cell lines under MTT test. The IC50 values characterizing the proliferation inhibition of HCT116, MS, RD TE32, and PC3 cells for the most active 2-cyano-24,24-dibromo-19β,28-epoxy-3,4-seco-3,23-dinor-18αH-olean-4-one 7 spanned the range 2.06–7.51 μM.

Cyclizations of The Isothiocyanates‐Derived Azatrienes: The CuBr–Catalyzed Switching from Thiophenes to Pyrroles

Azatrienes, alkyl 2‐alkoxy‐N‐buta‐2,3‐dienimidothioates, prepared from isothiocyanates, lithiated alkoxyallenes, and alkyl 2‐bromoacetates, readily cyclize in the presence of CuBr to selectively give rare functionalized pyrroles in up to 82 % yield that contrasts with the base‐catalyzed cyclization of the same azatrienes affording only thiophenes. This switching becomes possible due to the preisolation of azatrienes and their further contact with CuBr (6–9 mol‐%). A synthetically convenient route to so far inaccessible densely functionalized pyrroles has been developed.

Withaferin A and Withanolide D Analogues with Dual Heat-Shock-Inducing and Cytotoxic Activities: Semisynthesis and Biological Evaluation.

Withanolides constitute a valuable class of bioactive natural products because some members of the class are known to exhibit cytotoxic activity and also induce a cytoprotective heat-shock response. In order to understand the relationship between their structures and these dual bioactivities of the withanolide scaffold, we obtained 25 analogues of withaferin A (WA) and withanolide D (WD) including 17 new compounds by semisynthesis involving chemical and microbial transformations. Hitherto unknown 16β-hydroxy analogues of WA and WD were prepared by their reaction with triphenylphosphine/iodine, providing unexpected 5β-hydroxy-6α-iodo analogues (iodohydrins) followed by microbial biotransformation with Cunninghamella echinulata and base-catalyzed cyclization of the resulting 16β-hydroxy iodohydrins. Evaluation of these 25 withanolide analogues for their cytotoxicity and heat-shock-inducing activity (HSA) confirmed the known structure-activity relationships for WA-type withanolides and revealed that WD analogues were less active in both assays compared to their corresponding WA analogues. The 5β,6β-epoxide moiety of withanolides contributed to their cytotoxicity but not HSA. Introduction of a 16β-OAc group to 4,27-di- O-acetyl-WA enhanced cytotoxicity and decreased HSA, whereas introduction of the same group to 4- O-acetyl-WD decreased both activities.

Total Synthesis and Structure Revision of (±)-Clavilactone D Through Selective Cyclization of an α,β-Dicarbonyl Peroxide.

The structure of (±)-clavilactone D was revised, and the synthesis was achieved in seven steps from a substituted benzaldehyde. The key step was the base-catalyzed cyclization of an α,β-carbonyl peroxide, which was obtained by an iron-catalyzed three-component reaction of a benzaldehyde, an alkene, and TBHP. NaBH4-mediated reductive lactonization of the resulting cis-dicarbonyl epoxide led to the α,β-epoxy-γ-butyrolactone skeleton highly stereoselectively. The synthesis provides a concise, reliable, and practical route to the revised structure of clavilactone D.

Fast and efficient synthesis of flavanones from cinnamic acids

ABSTRACTA fast and efficient synthesis of flavanones from cinnamic acids in three steps has been developed. First, the cinnamic acid was converted to cinnamyol chlorides using SOCl2. The acid chlorides were then treated with substituted phenols in BF3 · OEt2 to furnish corresponding chalcones in 42(75% yields. Base-catalyzed cyclization of the chalcones at room temperature afforded corresponding flavones in 85–95% yields. The conversion of the cinnamic acid derivatives to corresponding chalcones was found to be sensitive to the position and nature of the substituents on the aromatic rings.