Nonpeptide angiotensin II receptor antagonists. Synthesis and biological activity of benzimidazolecarboxylic acids

Medicinal (Radio) Chemistry: Building Radiopharmaceuticals for the Future

Radiopharmaceuticals are increasingly playing a leading role in diagnosing, monitoring, and treating disease. In comparison with conventional pharmaceuticals, the development of radiopharmaceuticals does follow the principles of medicinal chemistry in the context of imaging-altered physiological processes. The design of a novel radiopharmaceutical has several steps similar to conventional drug discovery and some particularity. In the present work, we revisited the insights of medicinal chemistry in the current radiopharmaceutical development giving examples in oncology, neurology, and cardiology. In this regard, we overviewed the literature on radiopharmaceutical development to study overexpressed targets such as prostate-specific membrane antigen and fibroblast activation protein in cancer; β-amyloid plaques and tau protein in brain disorders; and angiotensin II type 1 receptor in cardiac disease. The work addresses concepts in the field of radiopharmacy with a special focus on the potential use of radiopharmaceuticals for nuclear imaging and theranostics.

Growing Utilization of Radical Chemistry in the Synthesis of Pharmaceuticals

Our current unhealthy lifestyle and the exponential surge in the population getting affected by a variety of diseases have made pharmaceuticals or drugs an imperative part of life, making the development of innovative strategies for drug discovery or the introduction of refined, cost-effective and modern technologies for the synthesis of clinically used drugs, a need of the hour. Ever since their discovery, free radicals and radical cations or anions as reactive intermediates have captivated the chemists, resulting in an exceptional utilization of these moieties throughout the field of chemical synthesis, owing to their unprecedented and widespread reactivity. Sticking with the idea of not judging the book by its cover, despite the conventional thought process of radicals being unstable and difficult to control entities, scientists and academicians around the globe have done an appreciable amount of work utilizing both persistent as well as transient radicals for a variety of organic transformations, exemplifying them with the synthesis of significant biologically active pharmaceutical ingredients. This review truly accounts for the organic radical transformations including radical addition, radical cascade cyclization, radical/radical cross-coupling, coupling with metal-complexes and radical cations coupling with nucleophiles, that offers fascinating and unconventional approaches towards the construction of intricate structural frameworks of marketed APIs with high atom- and step-economy; complementing the otherwise employed traditional methods. This tutorial review presents a comprehensive package of diverse methods utilized for radical generation, featuring their reactivity to form critical bonds in pharmaceutical total synthesis or in building key starting materials or intermediates of their synthetic journey, acknowledging their excellence, downsides and underlying mechanisms, which are otherwise poorly highlighted in the literature. Despite great achievements over the past few decades in this area, many challenges and obstacles are yet to be unraveled to shorten the distance between the academics and the industry, which are all discussed in summary and outlook.

Facile Synthesis of Benzimidazoles via N-Arylamidoxime Cyclization

A facile synthesis of benzimidazoles was described by a one-pot process containing acylation-cyclization of N-arylamidoxime. This method provided an alternative synthesis of benzimidazoles with a certain diversity of substituted groups in acceptable yields (up to 96%). More importantly, the construction of bis-benzimidazole (8), the key intermediate for making telmisartan, was achieved by adopting this method that enabled avoiding the undesired nitration with nitric/sulfuric acid and the cyclization in polyphosphoric acid in the existing operations.

Copper(II) mediated ortho C-H alkoxylation of aromatic amines using organic peroxides: efficient synthesis of hindered ethers

Synthesis of hindered alkyl aryl ether derivatives (R-O-Ar) remains a huge challenge and highly desirable in organic and medicinal chemistry because extensive substitution on the ether bond prevents the undesired metabolic process and thus avoids rapid degradation in vivo. Herein, we report an unprecedented hindered alkoxylation of picolinamide attached aromatic amines using economic copper salt and organic peroxide to get highly desirable α-tertiary alkyl aryl ethers.

Regioselective C-H Azidation of Anilines and Application to Synthesis of Key Intermediate for Pharmaceutical

A catalytic system for regioselective C-H azidation of inactive anilines was developed. In the presence of CuSO₄·5H₂O, simultaneous addition of NaN₃ and Na₂S₂O₈ to aq. CH₃CN solution of free anilines under weakly acidic conditions (pH 4.5) smoothly underwent C-H azidation to provide corresponding α-azidated products in high yields. Methyl α-azidoanthranilate obtained by this method was readily transformed via simple reduction followed by cyclization to methyl 2-ethoxybenzimidazol-7-carboxylate, a key intermediate for antihypertensive Candesartan Cilexetil.

Development of a novel [18 F]fluorobenzyl derivative of the AT1 receptor antagonist Candesartan

Candesartan is a clinically approved angiotensin II type 1 receptor (AT1 R)-blocker that selectively binds AT1 Rs in high affinity. We report here the radiosynthesis and automation of the novel [18 F]fluorobenzyl derivative of Candesartan using the Sonogashira cross-coupling reaction. [18 F]Fluorobenzyl-Candesartan ([18 F]7) was developed from 4-[18 F]fluoroiodobenzene ([18 F]FIB) that was conjugated with alkyne-trityl-candesartan with the assistance of a Pd (PPh3 )4 /CuI catalyst followed by acid deprotection. The three-step two-reactor 2-HPLC purification process was automated resulting in >90% pure [18 F]7 in a RCY of 4.6 ± 1.1% (decay corrected from EOB) and molar activities of 1,406-5,513 GBq/mmol. [18 F]FIB was reproducibly obtained by direct radiofluorination of the mono-iodinated triphenylsulfonium salt in the presence of K222/K2 CO3 in an ~30% yield (decay-corrected). [18 F]7 was stable (>97%) up to 4 h in solution and up to 1 h in rat plasma at 37°C. However, the use of Sonogashira cross-coupling reaction to produce [18 F]7 in high yields and molar activities was found to be challenging for routine use in radiochemistry labs.

Recent Advances in Therapeutic Applications of Bisbenzimidazoles

Nitrogen-containing heterocycles are one of the most common structural motifs in approximately 80% of the marketed drugs. Of these, benzimidazoles analogues are known to elicit a wide spectrum of pharmaceutical activities such as anticancer, antibacterial, antiparasitic, antiviral, antifungal as well as chemosensor effect. Based on the benzimidazole core fused heterocyclic compounds, crescent-shaped bisbenzimidazoles were developed which provided an early breakthrough in the sequence-specific DNA recognition. Over the years, a number of functional variations in the bisbenzimidazole core have led to the emergence of their unique properties and established them as versatile ligands against several classes of pathogens. The present review provides an overview of diverse pharmacological activities of the bisbenzimidazole analogues in the past decade with a brief account of its development through the years.

Development of novel benzimidazole-derived neddylation inhibitors for suppressing tumor growth invitro and invivo

Ubiquitin-like protein neddylation is overactivated in various human cancers and correlates with disease progression, and targeting this pathway represents a valuable therapeutic strategy. Our previous work disclosed an antihypertensive agent, candesartan cilexetic (CDC), serves as a novel neddylation inhibitor for suppressing tumor growth by targeting Nedd8-activating enzyme (NAE). In this study, 42 benzimidazole derivatives were designed and synthesized based on lead compound CDC to improve the neddylation inhibition and anticancer efficacy. Optimal benzimidazole-derived 35 displayed superior neddylation inhibition in enzyme assay compared to CDC (IC50 = 5.51 μM vs 16.43 μM), along with promising target inhibitory activity and killing selectivity in cancer cell. The results of cellular mechanism research combined with tumor growth suppression in human lung cancer cell A549 in vivo, accompanied with docking model, revealed that 35 has the potential to be developed as a promising neddylation inhibitor for anticancer therapy.

Application of organometallic catalysts for the synthesis of o-tolyl benzonitrile, a key starting material for sartans

This review describes methods for the synthesis of o-tolyl benzonitrile, such as Pd-, Ni-catalyzed Suzuki, Negishi and Kumada couplings reactions.

Generation of Sulfonylated Tetrazoles through an Iron-Catalyzed Multicomponent Reaction Involving Sulfur Dioxide

As a privileged motif, tetrazoles can be widely found in pharmaceuticals and materials science. Herein, a five-component reaction of cycloketone oxime esters, alkynes, DABCO·(SO₂)₂, and two molecules of trimethylsilyl azide under iron catalysis is developed, giving rise to a range of cyano-containing sulfonylated tetrazoles in moderate to good yields. This multicomponent reaction exhibits excellent selectivity and enables the formation of multiple new chemical bonds in one pot. A possible mechanism involving azidosulfonylation of alkynes, C-C bond cleavage of both cycloketone oxime esters and alkynes, and [3 + 2] cycloaddition of trimethylsilyl azide and the nitrilium cation intermediate is proposed. Additionally, the potential of terminal alkynes acting as powerful synthons for the synthesis of tetrazoles in a radical initiated process is demonstrated for the first time.

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High-value tetrazole motifs were synthesized via a five-component reaction

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Fixing sulfur dioxide into tetrazole molecules under mild conditions

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Low-cost iron catalyst initiated the transformation

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Excellent selectivity with the formation of multiple new chemical bonds

Synthesis of the Novel AT1 Receptor Tracer [18F]Fluoropyridine-Candesartan via Click Chemistry

A novel 7-((4-(3-((2-[¹⁸F]fluoropyridin-3-yl)oxy)propyl)-1H-1,2,3-triazol-1-yl)methyl)-1H-benzo[d]imidazole derivative of the angiotensin II type-1 receptor (AT₁R) blocker candesartan, [¹⁸F]fluoropyridine-candesartan, was synthesized via the copper-catalyzed azide-alkyne cycloaddition click reaction between 2-[¹⁸F]fluoro-3-(pent-4-yn-1-yloxy)pyridine ([¹⁸F]FPyKYNE) and the tetrazole-protected azido-candesartan derivative, followed by acid deprotection. This three-step, two-pot, and two-step purification synthesis was done within 2 h. The use of tris[(1-hydroxypropyl-1H-1,2,3-triazol-4-yl)methyl]amine (THPTA) as a Cu(I) stabilizing agent increased the overall radiochemical yield by 4-fold (10 ± 2%, n = 13) compared to the reaction without THPTA (2.4 ± 0.2%, n = 3; decay-corrected from ¹⁸F produced at the end-of-beam). Complete separation of [¹⁸F]FPyKYNE from its nitro precursor and [¹⁸F]fluoropyridine-candesartan from the deprotected azido-candesartan allowed for high molar activities (>380 GBq/μmol) of the tracer. The use of 0.1% trifluoroacetic acid in water for reformulation and the addition of sodium ascorbate to the final formulation (1.6 ± 0.2 GBq/mL, n = 3) prevented tracer radiolysis with >97% radiochemical purity for a period of up to 10 h after the end-of-synthesis. A significant reduction in the uptake (86 ± 3%, n = 8) of the tracer was observed ex vivo in rats (at 20 min postinjection) in the AT₁R-rich kidney cortex following pretreatment with saturating doses of the AT₁R antagonist candesartan or losartan. This specific binding to AT₁R was confirmed in vitro in the rat renal cortex (autoradiography) by a reduction of 26 ± 5% (n = 12) with losartan coincubation (10 μM). These favorable binding properties support further studies to assess the potential of [¹⁸F]fluoropyridine-candesartan as a tracer for the positron emission tomography imaging of renal AT₁R.

The design, synthesis and evaluation of 2-aminobenzoxazole analogues as potent and orally efficacious ChemR23 inhibitors

We previously reported 2-aminobenzoxazole analogue 1 as a potent ChemR23 inhibitor. The compound showed inhibitory activity against chemerin-induced calcium signaling through ChemR23 internalization in CAL-1 cells, which are cell lines of plasmacytoid dendric cells (pDCs). Furthermore, compound 2 inhibited chemotaxis of CAL-1 triggered by chemerin in vitro. However, we noted a difference in the ChemR23 response to our inhibitor between rodents and non-rodents in a previous study. To address this issue, we performed optimization of ChemR23 inhibitors using CAL-1 cells endogenously expressing human ChemR23 and conducted a pharmacokinetics study in cynomolgus monkeys. Various substituents at the 4-position of the benzoxazole ring exhibited potent in vitro bioactivity, while those at the 6-position were not tolerated. Among substituents, a carboxyl group was identified as key for improving the oral bioavailability in cynomolgus monkeys. Compound 38a with the acidic part changed from a tetrazole group to a 1,2,4-oxadiazol-5-one group to improve bioactivity and pharmacokinetic parameters exhibited inhibitory activity against chemerin-induced chemotaxis in vitro. In addition, we confirmed the ChemR23 internalization of pDCs by compound 38a orally administered to cynomolgus monkeys. These 2-aminobenzoxazole-based ChemR23 inhibitors may be useful as novel immunotherapeutic agents capable of suppressing the migration of pDCs, which are known to be major producers of type I interferons in the lesion area of certain autoimmune diseases, such as systemic lupus erythematosus and psoriasis.

Azilsartan medoxomil

Azilsartan is used for treatment of the high blood pressure (hypertension). Reducing high blood pressure enables avoid strokes, heart attacks and problems of kidneys. Azilsartan comes under the name angiotensin receptor blocker (ARBs) as a class of drugs. It acts by relaxing blood vessels to make it easier for blood to flow. Azilsartan Medoxomil's a comprehensive profile containing the description, formulae, Elemental Analysis, Uses and application. Furthermore, methods and schemes are outlined for the preparation of the drug substance. The physical properties of the medication include constant of ionization, solubility, X-ray powder diffraction pattern, differential scanning calorimetry, thermal conduct and spectroscopic studies are investigated. The methods employed in bulk medicines and/or in pharmaceutical formulations to analyze the drug substance include spectrophotometric, electrochemical and the chromatographic methods. Other studies on this drug substance include drug stability, Pharmaceutical Applications, Mechanism of Action, Pharmacodynamics, and a Dosing Information are reviewed. At the end of this profile, there are more than sixty references were listed.

Chlorodifluoromethane as a C1 Synthon in the Assembly of N-Containing Compounds

The development of C1 synthons to afford the products that add one extra carbon has become an important research theme in the past decade, and significant progress has been achieved with CO₂, CO, HCOOH, and others as C1 units. Despite the great advance, the search for new C1 synthons that display unique reactivity, complement to the current C1 sources, and add more value to C1 chemistry is still desirable. Herein, we report a quadruple cleavage of chlorodifluoromethane to yield a C1 source, which was successfully employed in the construction of various N-containing compounds especially with pharmaceutical molecules under mild conditions. This strategy provides a useful method for late-stage modification of pharmaceutical compounds. Four bonds in ClCF₂H were orderly cleaved under basic conditions in the absence of transition metals. Preliminary mechanistic studies revealed that (E)-N-phenylformimidoyl fluoride intermediate is involved in this process by in situ¹H NMR studies and control experiments.

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Quadruple cleavage of ClCF₂H to afford a C1 synthon

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The cleavage of two stable C(sp³)-F bonds in aliphatic gem-difluoroalkanes

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Enrich C1 chemistry, green chemistry, and fluorine chemistry

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Various N-containing compounds were afforded via different role of ClCF₂H

Synthesis and characterization of related substances of Azilsartan Kamedoxomil

Azilsartan Kamedoxomil is an AT1-subtype angiotensin II receptor blocker (ARB). During the laboratory synthesis of Azilsartan Kamedoxomil, four related substances of Azilsartan Kamedoxomil were observed and identified. These were 2-Ethoxy-3-[[4-[2- [4-[(5-methyl-2-oxo-1,3-dioxol-4-yl)methyl]-5-oxo-1,2,4-oxadiazol-3-yl]phenyl]phenyl] methyl] benzimidazole-4-carboxylic acid (azilsartan N-medoxomil, 9), (5-methyl-2-oxo- 1,3-dioxol-4-yl)methyl 2-ethoxy-3-[[4-[2-[4-[(5-methyl-2-oxo-1,3-dioxol-4-yl)methyl]-5- oxo-1,2,4-oxadiazol-3-yl]phenyl]phenyl] methyl] benzimidazole-4-carboxylate (azilsartan dimedoxomil, 10), (5-methyl-2-oxo-1,3-dioxo-4-yl)methyl 1-[2’-(4,5-dihydro-5-oxo-4H- 1,2,4-oxadiazol-3-yl)biphenyl-4-yl]methyl]-2-methoxy-1H-benzimidazole-7-carboxylate (methoxy analogue of azilsartan medoxomil, 11), Methyl 1-((2’-amidobiphenyl-4-yl) methyl)-2-ethoxy-1H-benzo[d]imidazole-7-carboxylate (amide methyl ester, 12). The present work describes the origin, synthesis and characterization of these related substances.

[3+2] Cycloaddition of azide with aldehyde hydrazone through an aminyl radical-polar crossover strategy

A novel approach to obtain functionalized tetrazoles through an aminyl radical-power crossover strategy is reported.

Synthesis and Crystal Structures of Benzimidazole-2-thione Derivatives by Alkylation Reactions

Alkylated, benzylated and bromoalkylated benzimidazole-thione that intramolecularly heterocyclized to 3,4-dihydro-2H-[1,3]thiazino[3,2-a]benzimidazole were synthesized. The chemical structure of the synthesized product was characterized by Infra Red, ¹H-NMR, ¹³C-NMR, and Mass spectroscopy. Furthermore, the molecular structures of 8 and 9 were confirmed by X-ray single crystallography in different space groups, Pbca and P2₁/c, respectively.

Discovery of Potent Antihypertensive Ligands Substituted Imidazolyl Biphenyl Sulfonylureas Analogs as Angiotensin II AT1 Receptor Antagonists by Molecular Modelling Studies

To elucidate the structural properties required for antihypertensive activity, three different molecular modelling techniques, two-dimensional quantitative structure activity relationship (2D-QSAR), group-based quantitative structure activity relationship (G-QSAR), and three-dimensional quantitative structure activity relationship (3D-QSAR) studies, have been carried out on a series of substituted imidazolyl biphenyl sulfonylureas derivatives. Multiple linear regressions methodology, viz. variable simulated annealing and stepwise methods, was applied to derive models which were further validated for statistical significance and predictive ability by internal and external validation. The best 2D-QSAR model was selected, having showed best predictability of activity with cross-validated value [Formula: see text], coefficient of determination [Formula: see text]. The [Formula: see text]_pred value of 0.7651 indicates predictability of test set analogues and reveals a significant and robust model, and best G-QSAR model having [Formula: see text] and [Formula: see text] with pred_[Formula: see text] was developed by SA-MLR. Using k-nearest neighbour approach, various 3D-QSAR models were generated and selected on the basis of [Formula: see text] and predictive [Formula: see text] values. The analysed best 3D-QSAR model revealed a good fit, having [Formula: see text] value of 0.8240 and [Formula: see text] value of 0.7523. The predictive power of the model generated was validated using a test set comprising molecules with pred_[Formula: see text] value of 0.7299. The results of two-dimensional QSAR and group-based QSAR showed that a combination of revealed the key role of Baumann's alignment-independent topological descriptors along with other descriptors such as the number of SsssCH count, SaasCE-index, SsOHcount indices properties could be explored to design potent antihypertensive agents. Finally, it is hoped that the work presented here will play an important role in understanding the relationship of physiochemical parameters with structure and biological activity.

Design, synthesis and biological activity of 4′-[(benzimidazol-1-yl)methyl]biphenyl-2-sulphonamides as dual angiotensin II and endothelin A receptor antagonists

A series of novel 4′-[(benzimidazol-1-yl)methyl]biphenyl-2-sulphonamides was designed, and their molecular model simulation fitting to a new HipHop 3D pharmacophore model was examined.

Copper(ii)-catalyzed methoxylation of unactivated (hetero)aryl C–H bonds using a removable bidentate auxiliary

A copper-catalyzed methoxylation of unactivated (hetero)aryl C–H bonds has been developed.

Discovery of potent antihypertensive ligands substituted imidazolyl biphenyl sulfonylureas analogs as angiotensin II AT1 receptor antagonists by molecular modelling studies

To elucidate the structural properties required for antihypertensive activity, three different molecular modeling techniques; two-dimensional Quantitative structure activity relationship (2D-QSAR), Group-Based Quantitative structure activity relationship (G-QSAR), and three-dimensional Quantitative structure activity relationship (3D-QSAR) studies have been carried out on a series of substituted imidazolyl biphenyl sulfonylureas derivatives. Multiple linear regressions methodology, viz. variable simulated annealing (SA) and stepwise (SW) methods, was applied to derive models which were further validated for statistical significance and predictive ability by internal and external validation. The best 2D-QSAR model was selected, having showed best predictability of activity with cross validated value (q2) = 0.7866, coefficient of determination (r2) =0.8003. The r2_pred value of 0.7651 indicates predictability of test set analogues and reveals a significant and robust model and best G-QSAR model having r2 = 0.7459 and q2 = 0.6712 with pred_r2 = 0.7105 was developed by SA -MLR. Using k-nearest neighbour (kNN) approach, various 3D QSAR models were generated and selected on the basis of q2 and predictive r2 values. The analyzed best 3D-QSAR model revealed a good fit, having r2 value of 0.8240 and q2 value of 0.7523. The predictive power of the model generated was validated using a test set comprising molecules with pred_r2 value of 0.7299. The results of two-dimensional QSAR, Group based QSAR showed that a combination of revealed the key role of Baumann's alignment independent topological descriptors along with other descriptors such as the number of hydrogen bond acceptors, hydrogen bond donors, rotatable bonds indices properties and auto-correlation descriptors of different atomic properties could be explored to design potent antihypertensive agents. Finally, it is hoped that the work presented here will play an important role in understanding the relationship of physiochemical parameters with structure and biological activity.

Design, synthesis, pharmacological evaluation and in silico ADMET prediction of novel substituted benzimidazole derivatives as angiotensin II-AT1 receptor antagonists based on predictive 3D QSAR models

In this study we designed novel substituted benzimidazole derivatives and predicted their absorption, distribution, metabolism, excretion and toxicity (ADMET) properties, based on a predictive 3D QSAR study on 132 substituted benzimidazoles as AngII-AT1 receptor antagonists. The two best predicted compounds were synthesized and evaluated for AngII-AT1 receptor antagonism. Three different alignment tools for comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were used. The best 3D QSAR models were obtained using the rigid body (Distill) alignment method. CoMFA and CoMSIA models were found to be statistically significant with leave-one-out correlation coefficients (q(2)) of 0.630 and 0.623, respectively, cross-validated coefficients (r(2)cv) of 0.651 and 0.630, respectively, and conventional coefficients of determination (r(2)) of 0.848 and 0.843, respectively. 3D QSAR models were validated using a test set of 24 compounds, giving satisfactory predicted results (r(2)pred) of 0.727 and 0.689 for the CoMFA and CoMSIA models, respectively. We have identified some key features in substituted benzimidazole derivatives, such as lipophilicity and H-bonding at the 2- and 5-positions of the benzimidazole nucleus, respectively, for AT1 receptor antagonistic activity. We designed 20 novel substituted benzimidazole derivatives and predicted their activity. In silico ADMET properties were also predicted for these designed molecules. Finally, the compounds with best predicted activity were synthesized and evaluated for in vitro angiotensin II-AT1 receptor antagonism.

2-(3,4-Di-fluoro-phen-yl)-1H-benzimidazole

In the title mol-ecule, C13H8F2N2, the dihedral angle between the benzimidazole ring system and the di-fluoro-substituted benzene ring is 30.0 (1)°. In the crystal, mol-ecules are linked by N-H⋯N hydrogen bonds, forming chains along [010]. In addition, weak C-H⋯F hydrogen bonds connect chains into a two-dimensional network parallel to (001). A weak C-H⋯π inter-action is observed between an H atom of the benzimidazole ring sytem and the π system of the di-fluoro-substituted benzene ring.

Pyrimido[5,4-e]tetrazolo[5,1-b][1,3,4]thiadiazines as a new heterocyclic system

Six novel 2-substituted pyrimido[5,4- e]tetrazolo[5,1- b][1,3,4]thiadiazines were prepared via a multistep synthetic sequence beginning with 5-bromo-2,4-dichloro-6-methylpyrimidine.

Theoretical studies on the tautomerism of tetrazole selenone

The tautomerism of all possible forms of tetrazole selenone (A-G), induced by proton transfer, was studied, theoretically, in different environments including gas phase, continuum solvent and microsolvated environment with one or two explicit water or ammonia molecules. The calculations were performed using two different levels of theory including mPW2PLYP and DFT-B3LYP. The 6-311++G(d,p) basis set was used for C, H, O and N and the standard relativistic effective core pseudo potential LANL2DZ basis set was used for Se atom. It was found that the tetrazole selenone, in the form of A, is the most stable isomer in all of the environments considered in this work. The kinetics of proton transfer reaction was studied in both gas and solvent environments and it was concluded that the activation energy of the reaction increases with going from the gas phase to polar solvents. Moreover, the proton transfer reaction assisted by one or two water or ammonia molecules was investigated and it was found that the activation energy significantly reduces.