Moderate Yields Research Articles

Determination of aquifer hydraulic parameters and groundwater protective capacity in parts of Nsukwa clan, Nigeria.

The goal of this study is to determine aquifer parameters and groundwater protective capacity in parts of the Nsukwa clan using geoelectric and pumping test methods. Seventeen vertical electrical soundings were acquired to determine the geoelectric properties, while two wells were drilled to determine the lithology and the aquifer parameters of the area. The result showed that the lithology comprised lateritic topsoil and sand, fine sand, medium sand, and coarse sand, respectively. Geoelectric data interpretation using Win Resist software revealed a close correlation with the well record. Geoelectric data analysis indicated that prolific aquifer can be sourced within the third and fourth layers, located within 24.2-43.8m and comprised medium to coarse sand. The aquifer resistivity ranged from 703.1 to 26,367.7Ωm. The Dar Zarrouk parameters, such as transverse resistance (R) and longitudinal conductance (S), were applied to determine the aquifer transmissivity (T) and hydraulic conductivity (K). The computed T and K from geoelectric sounding ranged from 11.37 to 34.79m2/day, with a mean value of 18.51m2/day and 0.8243m/day, respectively, while the T and K values from the pumping test are 18.58m2/day and 0.8251m/day, respectively. S and R values ranged from 0.001179 to 0.0131619Ω-1 and 2434 to 102,090Ωm2, respectively, revealing a poor aquifer protective capacity and moderate yield. The storativity and storage coefficient of the aquifer values of 0.0023 and 0.072m2/min, respectively, revealed a confined aquifer capable of providing sufficient water to the people. These findings showed moderate aquifer potential with poor protective capacity; thus, adequate aquifer protective strategies are recommended.

Organocatalytic Enantioselective (4+2) Annulation of Cyclopropane Carbaldehydes with 2‐Mercapto‐1‐Arylethanones

AbstractHere, we report the organocatalytic enantioselective synthesis of dihydrothiopyran derivatives from trans racemic donor–acceptor cyclopropane carbaldehydes (DACCs) and 2‐mercapto‐1‐arylethanone via formal thio (4+2) cycloaddition involving thia‐Michael aldol condensation and annulation. Mechanistic studies indicate a typical kinetic resolution (KR) is involved in this transformation, which results in moderate yields and enantiomeric ratios. Remarkably, this method is characterized by its one‐pot simplicity, mild reaction conditions, and resilience towards air and moisture interference.

Synthesis of V-shaped Thiophene Based Rotor-Stilbene: Substituent Dependent Aggregation and Photophysical Properties.

Thiophene core V-shaped rotor-stilbene derivatives have been synthesized utilizing two-fold Heck coupling reaction. These compounds are blue emitters with moderate quantum yield in dilute solution. Rotor nature of the synthesized stilbenes supports aggregation induced emission (AIE) behaviour and they show substituent dependent emission behavior in aggregate state. In presence of donating groups (e.g., tert-butyl, methoxy, diphenylamine group) in stilbenes, they exhibit AIE property. But with the introduction of electron withdrawing group (nitro group), they shows aggregation caused quenching (ACQ) behavior. Different types of nano-aggregates formation is observed in aggregated state, which was confirmed by dynamic light scattering (DLS) and scanning electron microscopy (SEM) studies. The details photophysical (absorption, fluorescence, and lifetime), electrochemical property (cyclic voltammetry) and thermal stability have been investigated. Optimized structure, energy and electronic distribution of molecular orbitals have been studied by theoretical calculation.

Chemoselective Synthesis of Unsymmetrical Dithioacetals through Sequential Carbene Insertion and Acetal Exchange of Acylsilanes and Thiols under Visible Light Irradiation.

Dithioacetals are a frequently used motif in synthetic organic chemistry, and most existing reports discuss only symmetrical dithioacetals. Examples of unsymmetrical dithioacetals are scarce, and few general methods for the selective synthesis of these compounds exists. An intriguing visible-light-induced strategy has been established in this work for sequential reactions of S-H insertion and acetal exchange between acylsilanes and two different thiols that deliver a wide variety of unsymmetrical dithioacetals in moderate yields. The unsymmetrical dithioacetals were obtained with high selectivity, and a great variety of functional groups were tolerated.

Novel Benzotriazole-β-lactam Derivatives as Antimalarial Agents: Design, Synthesis, Biological Evaluation and Molecular Docking Studies.

Many people around the world suffer from malaria, especially in tropical or subtropical regions. While malaria medications have shown success in treating malaria, there is still a problem with resistance to these drugs. Herein, we designed and synthesized some structurally novel benzotriazole-β-lactams using 2-(1H-benzo[d][1,2,3]triazol-1-yl)acetic acid as a key intermediate. To synthesize the target molecules, the ketene-imine cycloaddition reaction was employed. First, The reaction of 1H-benzo[d][1,2,3]triazole with 2-bromoacetic acid in aqueous sodium hydroxide yielded 2-(1H-benzo[d][1,2,3]triazol-1-yl)acetic acid. Then, the treatment of 2-(1H-benzo[d][1,2,3]triazol-1-yl)acetic acid with tosyl chloride, triethyl amine, and Schiff base provided new β-lactams in good to moderate yields.The formation of all cycloadducts was confirmed by elemental analysis, FT-IR, NMR and mass spectral data. Moreover, X-ray crystallography was used to determine the relative stereochemistry of 4a compound. The in vitro antimalarial activity test was conducted for each compound against P. falciparum K1. The IC50 values ranged from 5.56 to 25.65 μM. A cytotoxicity profile of the compounds at 200 μM final concentration revealed suitable selectivity of the compounds for malaria treatment. Furthermore, the docking study was carried out for each compound into the P. falciparum dihydrofolate reductase enzyme (PfDHFR) binding site to analyze their possible binding orientation in the active site.

Direct Intramolecular Coupling of Primary/Secondary Alcohols with Secondary Alcohols for Macrocyclic Alkenylation Using Ni‐Zeolite Catalyst Under Continuous‐Flow Conditions

AbstractHerein, we report the direct intramolecular coupling of primary and secondary alcohols for the selective synthesis of macrocyclic olefins in the presence of Ni‐zeolite catalyst under continuous flow. This reaction proceeds via dehydration of secondary alcohols to alkenes, which subsequently undergo intramolecular dehydrative coupling reaction with a primary alcohol to obtain moderate yields of macrocyclic olefins. This reaction is also effective for the coupling of secondary‐secondary alcohols and alkene‐alcohols to produce diverse macrocyclic olefin products. This unique approach has various advantages including step‐economy, no additives and pre‐functionalization required, inexpensive and reusable catalyst, and exemplification with 23 macrocycles in different ring sizes. The continuous flow macrocyclisation afforded higher productivity and space‐time yield than the batch reaction conditions.

Synthesis of 2-Amino-N'-aroyl(het)arylhydrazides, DNA Photocleavage, Molecular Docking and Cytotoxicity Studies against Melanoma CarB Cell Lines.

Diacylhydrazine bridged anthranilic acids with aryl and heteroaryl domains have been synthesized as the open flexible scaffold of arylamide quinazolinones in order to investigate flexibility versus rigidity towards DNA photocleavage and sensitivity. Most of the compounds have been synthesized via the in situ formation of their anthraniloyl chloride and subsequent reaction with the desired hydrazide and were obtained as precipitates, in moderate yields. All compounds showed high UV-A light absorption and are eligible for DNA photocleavage studies under this "harmless" irradiation. Despite their reduced UV-B light absorption, a first screening indicated the necessity of a halogen at the p-position in relation to the amine group and the lack of an electron-withdrawing group on the aryl group. These characteristics, in general, remained under UV-A light, rendering these compounds as a novel class of UV-A-triggered DNA photocleavers. The best photocleaver, the compound 9, was active at concentrations as low as 2 μΜ. The 5-Nitro-anthranilic derivatives were inactive, giving the opposite results to their related rigid quinazolinones. Molecular docking studies with DNA showed possible interaction sites, whereas cytotoxicity experiments indicated the iodo derivative 17 as a potent cytotoxic agent and the compound 9 as a slight phototoxic compound.

Electrochemical bromination of electron-rich compounds employing LiBr as a “Br” source

A direct electrochemical-mediated CH bromination strategy of electron-rich compound is established using LiBr as a “Br” source under transition metal-free and oxidant-free catalysis condition. This method is performed in a green and sustainable system. A wide range of electron-rich compounds were found to be compatible, providing the corresponding products with moderate yields.

Synthesis of Heterodiarylmethanes via Metallaphotoredox Decarboxylative Arylation

AbstractA metallaphotoredox-catalyzed synthesis of heterodiarylmethanes using mild reaction conditions, commercially available substrates, and bench-stable catalysts is demonstrated. Moderate yields are obtained, and further derivatization of the newly formed benzylic position is shown.

Dinucleating N‐donor Ligands with 1,2‐Diethynylbenzene Backbone for the Copper‐Mediated Monooxygenation of Phenols

AbstractNew dinucleating, tweezer‐like ligands with 1,2‐diethynyl‐benzene backbone containing three pyridines (Tw1), a combination of pyridine and pyrazole (Tw2) or pyridine and triazole (Tw3), respectively, have been synthesized and characterized spectroscopically and by single crystal structure determination. The ability of the derived copper(I) complexes CuTw1–3 to act as model systems for tyrosinase (Ty) was investigated by studying the reactivity toward monophenolic substrates. No dioxygen intermediate was detected at low temperatures, and CuTw1 was found to be inactive toward monoxygenation of phenolic substrate DTBP‐H. However, a crystal structure containing a μ‐hydroxo ligand, similar to the met‐form of Ty, underlines the ability of the complex to bind oxygen. In contrast, CuTw2 converts phenols to o‐quinones with moderate yield and this activity is even higher when using CuTw3. The observed differences in reactivity are discussed.

Synthetic assembly of α-O-linked-type GlcNAc using polymer chemistry affords sugar clusters, which effectively bind to lectins

Fischer’s glycoside synthesis was applied to linker precursor alcohols of two different lengths having appropriate alkane chains to obtain the corresponding α-glycoside and it was found to be applicable with moderate yields. Water-soluble glycomonomers were systematically prepared from N-acetyl-d-glucosamine (GlcNAc) by introducing two kinds of alcohols having different methylene lengths. Typical radical polymerizations of the glycomonomers with acrylamide as a modulator for control of the distance between carbohydrate residues in water in the presence of ammonium persulfate (APS)-N,N,N’,N’-tetramethylethylenediamine (TEMED) gave a series of glycopolymers with various α-glycoside-type GlcNAc residue densities. Fluorometric analysis of the interaction of wheat germ agglutinin (WGA) with the glycopolymers was performed and the results showed unique binding specificities based on structural differences.

CO2 to Cyclic Carbonate: A Mechanistic Insight of a Benign Route Using Zinc(II) Salophen Complexes

AbstractZinc(II) Schiff base complexes with different substituents at 5, 5’ positions have been synthesized to study the effect of the electronic environment of the metal towards the cycloaddition reaction between CO2 and epoxide. The complexes have been characterized by FT‐IR, XPS, NMR, electronic spectroscopy, LC–MS, and TGA. We have used density functional theory to study the electronic structure of the Zn(II) complexes and modelled the electronic spectra and the mechanism of catalysis. Results obtained from DFT and LC–MS indicate the dimeric structures for all the complexes except ZnL4. The monomeric ZnL4 has the strongest electron withdrawing group, i. e., −NO2 at 5, 5’ positions along with two labile water molecules attached to the Zn center. The dimeric complexes exhibit good to moderate yield for cycloaddition reaction to styrene carbonate under solvent‐free conditions and a relatively low reaction temperature of 80 °C, with CO2 pressure of ~1 atm. The best yield has been achieved by ZnL4. Different rate‐determining steps are captured by the DFT studies for dimeric and monomeric complexes. Without taking any preventing measure of dimerization by attaching the bulky tBu groups, relatively lesser catalytic amounts of all the complexes have shown yields of cyclic carbonate between 53–74 %, depending on the nature of the substituent present.

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.

Sc(OTf)3‐catalyzed tandem (3+3)‐annulation/lactonization of cyclopropanes with salicylaldehyde nitrones to access polycyclic 1,2‐oxazines

AbstractA Sc(OTf)3‐catalyzed tandem (3 + 3)‐annulation/lactonization of donor‐acceptor cyclopropane 1,1‐dieters with salicylaldehyde nitrones has been reported, affording a wide range of tetrahydrochromeno[4,3‐c][1,2]oxazin‐5(1H)‐ones in moderate yields with excellent diastereoselectivities. Besides, the gram‐scale reaction has also been explored to demonstrate the utility of this protocol. Moreover, the mechanism was investigated through control experiments, which show the reaction proceeds via a tandem (3 + 3)‐annulation/lactonization reaction.

A facile synthesis of precursor for the σ-1 receptor PET radioligand [18 F]FTC-146 and its radiofluorination.

The σ-1 receptor is a non-opioid transmembrane protein involved in various human pathologies including neurodegenerative diseases, inflammation, and cancer. The previously published ligand [18 F]FTC-146 is among the most promising tools for σ-1 molecular imaging by positron emission tomography (PET), with a potential for application in clinical diagnostics and research. However, the published six- or four-step synthesis of the tosyl ester precursor for its radiosynthesis is complicated and time-consuming. Herein, we present a simple one-step precursor synthesis followed by a one-step fluorine-18 labeling procedure that streamlines the preparation of [18 F]FTC-146. Instead of a tosyl-based precursor, we developed a one-step synthesis of the precursor analog AM-16 containing a chloride leaving group for the SN 2 reaction with 18 F-fluoride. 18 F-fluorination of AM-16 led to a moderate decay-corrected radiochemical yield (RCY = 7.5%) with molar activity (Am ) of 45.9GBq/μmol. Further optimization of this procedure should enable routine radiopharmaceutical production of this promising PET tracer.

Regio- and Stereoselective Hexafluoroisopropoxylation and Trifluoroethoxylation of Allenamides.

Incorporating fluorinated moieties into organic molecules is an attractive strategy to enhance drug-like properties. Herein, we have developed a simple and self-promoted protocol for hexafluoroisopropoxylation and trifluoroethoxylation of allenamides with fluorinated alcohols such as HFIP and TFE. The reaction provided the fluoroalkoxylated products in a regio- and stereoselective manner in good to moderate yields under mild conditions.

Clay-supported bio-based Lewis acid ionic liquid as a potent catalyst for the dehydration of fructose to 5-hydroxymthylfurfural

Caffeine and halloysite nanoclay mineral that are bio-based compounds were utilized to synthesize a novel Lewis acid heterogeneous catalyst. To this aim, halloysite was functionalized with 2,4,6-trichloro-1,3,5-triazine and reacted with caffeine, which was then converted to ionic liquid via a reaction with ZnCl2. The catalyst was applied for promoting the dehydration of fructose to 5-hydroxymethylfurfural. To investigate the effects of the reaction variables, response surface methodology was used. The product was achieved in 98.5% in 100 min using a catalyst loading of 30 wt% at 100 °C. Moreover, the catalyst was recyclable up to six runs with slight zinc leaching. Comparison of the catalytic activity of the catalyst with that of halloysite and a control catalyst with one caffeine-based Lewis acid ionic liquid confirmed the superior activity of the former and the important role of 2,4,6-trichloro-1,3,5-triazine for increasing the number of the grafted caffeine and thus the acidic sites of the catalyst. A plausible reaction mechanism was proposed, and the activity of the catalyst for other carbohydrates was also studied. According to the results, this catalyst catalyzed the reaction of other substrates to furnish 5-hydroxymethylfurfural in low to moderate yields. According to the kinetic studies, the activation energy was estimated to be 22.85 kJ/mol.

Coordination chemistry of alkali metal dimesityl-thio- and dimesityl-selenophosphinites [(L)2A-EPMes2]2 (A = Li, Na, K; E = S, Se; L = THF, THP) and [(18C6)K-SPMes2

The reactions of dimesitylphosphane oxide Mes2P(O)H with Lawessons reagent and dimesitylphoshane with selenium yield Mes2P(E)H with E = S (1a) and E = Se (1b), respectively, with moderate yields. Metalation of dimesitylphosphane sulfide 1a with n-butyllithium, sodium hydride or potassium hydride in THF allows the isolation of dinuclear dimesityl-thiophosphinites of the type [(thf)2A-S-PMes2]2 [A = Li (4), Na (5), K (2a)] with central four-membered A2S2 rings. The weaker base THP leads to the very similar aggregate [(thp)2K-S-PMes2]2 (3a) as has also been observed for the homologous potassium dimesityl-selenophosphinites of the type [(L)2K-Se-PMes2]2 [L = thf (2b), thp (3b)]. Addition of 18-crown-6 ether leads to deaggregation and expectedly to formation of mononuclear [(18C6)K-S-PMes2] (6). Moderate yields have been obtained due to dismutation reactions that yield the corresponding phosphinates AE2PMes2 and phosphanides APMes2, a degradation process which has been observed earlier also for Li-O-PMes2. This side reaction hampers the application of these thio- and selenophosphinites as catalysts in the addition of phosphane sulfides and selenides across alkynes.

A homoleptic Fe(iv) ketimide complex with a low-lying excited state.

The reaction of 4 equiv. of Li(N[double bond, length as m-dash]C( t Bu)Ph) with FeIICl2 results in isolation of [Li(Et2O)]2[FeII(N[double bond, length as m-dash]C( t Bu)Ph)4] (1), in good yields. The reaction of 1 with 1 equiv. of I2 leads to formation of [FeIV(N[double bond, length as m-dash]C( t Bu)Ph)4] (2), in moderate yields. 57Fe Mössbauer spectroscopy confirms the Fe(iv) oxidation state of 2, and X-ray crystallography reveals that 2 has a square planar coordination geometry along with several intramolecular H⋯C interactions. Furthermore, SQUID magnetometry indicates a small magnetic moment at room temperature, suggestive of an accessible S = 1 state. Both density functional theory and multiconfigurational calculations were done to elucidate the nature of the ground state. Consistent with the experimental results, the ground state was found to be an S = 0 state with an S = 1 excited state close in energy.

Iridium-catalyzed diacylmethylation of tyrosine and its peptides with sulfoxonium ylides.

Pyridyloxy-directed Ir(III)-catalyzed diacylmethylation of protected tyrosines was achieved with alkyl and (hetero)aryl sulfoxonium ylides, furnishing tyrosine-based unnatural amino acids in good yields. Furthermore, the late stage exemplification of the strategy was successfully accomplished in tyrosine-containing dipeptides, tripeptides and tetrapeptides in moderate yields. This methodology is distinguished by its site-selectivity, tolerance of sensitive functional groups, scalability, and retention of the chiral configuration for tyrosine motifs.