scholarly journals 5-Membered cyclic ethers via phenonium ion mediated cyclization through carbonate chemistry

2018 ◽  
Vol 90 (1) ◽  
pp. 93-107 ◽  
Author(s):  
Fabio Aricò ◽  
Andrea Maranzana ◽  
Manuele Musolino ◽  
Pietro Tundo
Keyword(s):  
Intramolecular Cyclization ◽  
Theoretical Calculations ◽  
Cyclic Ether ◽  
Hydroxyl Group ◽  
Cyclic Ethers ◽  
Carbonate Chemistry ◽  
Reaction Conditions ◽  
Leaving Group ◽  
Acidic Conditions ◽  
First Time

AbstractCyclization of 2-(2-hydroxyethyl)phenol via DMC chemistry in acidic conditions is herein discussed for the first time. Reaction conditions have been investigated and optimized. This substrate is quite appealing as it incorporates a 2-hydroxyethyl moiety in ortho to the aromatic hydroxyl group capable of stabilizing the related phenonium ion. When the reaction mechanism was investigated via theoretical calculations, the results suggest that the most favorable pathway encompasses a DMC-mediated formation of the phenonium ion that is converted into the 2-(2-methoxyethyl)phenol. The related cyclic ether is then formed via intramolecular cyclization of this intermediate. This peculiar cyclization reaction is another example of the versatility of DMC herein used as solvent, methoxycarbonylation agent and leaving group in the intramolecular cyclization leading to the phenonium ion.

α-Glucosidase Inhibition and Docking Studies of 5-Deoxyflavonols and Dihydroflavonols Isolated from Abutilon pakistanicum

2019 ◽  
Vol 23 (17) ◽  
pp. 1857-1866
Author(s):  
Munawar Hussain ◽  
Zaheer Ahmed ◽  
Shamsun N. Khan ◽  
Syed A. A. Shah ◽  
Rizwana Razi ◽  
...  
Keyword(s):  
Methanolic Extract ◽  
Docking Studies ◽  
Hydroxyl Group ◽  
Coumaric Acid ◽  
In Vitro Activity ◽  
Aerial Parts ◽  
First Time ◽  
Acid Esters ◽  
Phenol Moiety

Three new 5-deoxyflavonoid and dihydroflavonoids 2, 3 and 4 have been isolated from the methanolic extract of Abutioln pakistanicum aerial parts, for which structures were elucidated explicitly by extensive MS- and NMR-experiments. In addition to these, 3,7,4′-trihydroxy-3′-methoxy flavonol (1) is reported for the first time from Abutioln pakistanicum. Compound 2 and 4 are p-coumaric acid esters while compounds 2–4 exhibited α-glucosidase inhibitory activity. Docking studies indicated that the ability of flavonoids 2, 3 and 4 to form multiple hydrogen bonds with catalytically important residues is decisive hence is responsible for the inhibition activity. The docking results signified the observed in-vitro activity quite well which is in accordance with previously obtained conclusion that phenol moiety and hydroxyl group are critical for the inhibition of α-glucosidase enzyme.

Participation of 19-substituents in electrophilic additions to 6,7-unsaturated 5α-cholestane and B-homo 5α-cholestane derivatives; A case of competition between the participation of an ambident neighboring group and external nucleophile attack

1980 ◽  
Vol 45 (2) ◽  
pp. 559-583 ◽  
Author(s):  
Pavel Kočovský ◽  
Ladislav Kohout ◽  
Václav Černý
Keyword(s):  
Perchloric Acid ◽  
Hydrobromic Acid ◽  
Cyclic Ether ◽  
Cyclic Ethers ◽  
Neighboring Group ◽  
Acid Cleavage ◽  
Neighbouring Group Participation ◽  
Aqueous Perchloric Acid ◽  
The Difference ◽  
Electrophilic Additions

Hypobromous acid action upon the 6,7-unsaturated 19-substituted 5α-cholestans Va-Vc results in the formation of two types of products, the cyclic ethers IX as products of 5(O)n participation of the 19-substituent, and the bromohydrins X. All these compounds are formed from the 6α,7α-bromonium ions Va'-Vc'. Under the same conditions the B-homo-5α-cholestane derivatives VIIa-VIIc afforded solely the cyclic ethers XIV as products of 5(O)n participation of the 19-substituent in the cleavage of the bromonium ions VIIa'-VIIc'. Acid cleavage of the 6α,7α-epoxides VIb and VIc with aqueous perchloric acid or hydrobromic acid gave two types of products, i.e. the cyclic ethers XI and the diols XII or bromohydrines XIII. The cyclic ethers XI arise by 5(O)n participation of the 19-substituent. The B-homo-6α, 7α-epoxide VIIIc on cleavage with aqueous perchloric acid have solely the cyclic ether XVc and by treatment with hydrobromic acid VIIIc afforded the mixture of XVc, as the main product, and of the bromohydrin XVIc. Discussed is the similarity of the bromonium ion cleavage with the fission of the corresponding epoxides, the mechanism of these reactions and the difference in the behaviour of the isomeric olefins Ia-c, IIIa-c, Va-c and VIIa-c and epoxides IIb,c, IVb,c, VIb,c and VIIIb,c. The competition between ambident neighbouring group participation and external nucleophile attack is discussed as well as the dependence of the products ratio on the nucleophilicity of the attacking species.

scholarly journals A Sustainable Improvement of ω-Bromoalkylphosphonates Synthesis to Access Novel KuQuinones

Organics ◽  
2021 ◽  
Vol 2 (2) ◽  
pp. 107-117
Author(s):  
Mattia Forchetta ◽  
Valeria Conte ◽  
Giulia Fiorani ◽  
Pierluca Galloni ◽  
Federica Sabuzi
Keyword(s):  
Metal Oxides ◽  
Phosphonic Acid ◽  
Organic Molecules ◽  
Building Blocks ◽  
Reaction Conditions ◽  
Phosphonic Acids ◽  
Sustainable Improvement ◽  
Phosphonate Esters ◽  
First Time ◽  
Complex Organic

Owing to the attractiveness of organic phosphonic acids and esters in the pharmacological field and in the functionalization of conductive metal-oxides, the research of effective synthetic protocols is pivotal. Among the others, ω-bromoalkylphosphonates are gaining particular attention because they are useful building blocks for the tailored functionalization of complex organic molecules. Hence, in this work, the optimization of Michaelis–Arbuzov reaction conditions for ω-bromoalkylphosphonates has been performed, to improve process sustainability while maintaining good yields. Synthesized ω-bromoalkylphosphonates have been successfully adopted for the synthesis of new KuQuinone phosphonate esters and, by hydrolysis, phosphonic acid KuQuinone derivatives have been obtained for the first time. Considering the high affinity with metal-oxides, KuQuinones bearing phosphonic acid terminal groups are promising candidates for biomedical and photo(electro)chemical applications.

Sulfonyl Radical Triggered Selective Iodosulfonylation and Bicycli-zations of 1,6-Dienes

2021 ◽  
Author(s):  
Shi-Ping Wu ◽  
Dong-Kai Wang ◽  
Qing-Qing Kang ◽  
Guo-Ping Ge ◽  
Hongxing Zheng ◽  
...  
Keyword(s):  
Functional Group ◽  
High Selectivity ◽  
Reaction Conditions ◽  
First Time

A novel sulfonyl radical triggered selective iodosulfonylation and bicyclizations of 1,6-dienes has been described for the first time. High selectivity and efficiency, mild reaction conditions, excellent functional group compatibility, and...

scholarly journals Bufadienolides from the Skin Secretions of the Neotropical Toad Rhinella alata (Anura: Bufonidae): Antiprotozoal Activity against Trypanosoma cruzi

Molecules ◽  
2021 ◽  
Vol 26 (14) ◽  
pp. 4217
Author(s):  
Candelario Rodriguez ◽  
Roberto Ibáñez ◽  
Luis Mojica ◽  
Michelle Ng ◽  
Carmenza Spadafora ◽  
...  
Keyword(s):  
Vero Cells ◽  
Chemical Diversity ◽  
Hydroxyl Group ◽  
Antitrypanosomal Activity ◽  
The Family ◽  
Toad Venom ◽  
Skin Secretions ◽  
Pharmacological Potential ◽  
First Time ◽  
Mcf 7

Toads in the family Bufonidae contain bufadienolides in their venom, which are characterized by their chemical diversity and high pharmacological potential. American trypanosomiasis is a neglected disease that affects an estimated 8 million people in tropical and subtropical countries. In this research, we investigated the chemical composition and antitrypanosomal activity of toad venom from Rhinella alata collected in Panama. Structural determination using mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy led to the identification of 10 bufadienolides. Compounds identified include the following: 16β-hydroxy-desacetyl-bufotalin-3-adipoyl-arginine ester (1), bufotalin (2), 16β-hydroxy-desacetyl-bufotalin-3-pimeloyl-arginine ester (3), bufotalin-3-pimeloyl-arginine ester (4), 16β-hydroxy-desacetyl-bufotalin-3-suberoyl-arginine ester (5), bufotalin-3-suberoyl-arginine ester (6), cinobufagin-3-adipoyl-arginine ester (7), cinobufagin-3-pimeloyl-arginine ester (8), cinobufagin-3-suberoyl-arginine ester (9), and cinobufagin (10). Among these, three new natural products, 1, 3, and 5, are described, and compounds 1–10 are reported for the first time in R. alata. The antitrypanosomal activity assessed in this study revealed that the presence of an arginyl-diacid attached to C-3, and a hydroxyl group at C-14 in the structure of bufadienolides that is important for their biological activity. Bufadienolides showed cytotoxic activity against epithelial kidney Vero cells; however, bufagins (2 and 10) displayed low mammalian cytotoxicity. Compounds 2 and 10 showed activity against the cancer cell lines MCF-7, NCI-H460, and SF-268.

scholarly journals Insights on forming N,O-coordinated Cu single-atom catalysts for electrochemical reduction CO2 to methane

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yanming Cai ◽  
Jiaju Fu ◽  
Yang Zhou ◽  
Yu-Chung Chang ◽  
Qianhao Min ◽  
...  
Keyword(s):  
Energy Barrier ◽  
Active Sites ◽  
Theoretical Calculations ◽  
High Energy ◽  
Single Atom ◽  
Faradaic Efficiency ◽  
High Energy Barrier ◽  
Catalytic Sites ◽  
Electron Reduction ◽  
First Time

AbstractSingle-atom catalysts (SACs) are promising candidates to catalyze electrochemical CO2 reduction (ECR) due to maximized atomic utilization. However, products are usually limited to CO instead of hydrocarbons or oxygenates due to unfavorable high energy barrier for further electron transfer on synthesized single atom catalytic sites. Here we report a novel partial-carbonization strategy to modify the electronic structures of center atoms on SACs for lowering the overall endothermic energy of key intermediates. A carbon-dots-based SAC margined with unique CuN2O2 sites was synthesized for the first time. The introduction of oxygen ligands brings remarkably high Faradaic efficiency (78%) and selectivity (99% of ECR products) for electrochemical converting CO2 to CH4 with current density of 40 mA·cm-2 in aqueous electrolytes, surpassing most reported SACs which stop at two-electron reduction. Theoretical calculations further revealed that the high selectivity and activity on CuN2O2 active sites are due to the proper elevated CH4 and H2 energy barrier and fine-tuned electronic structure of Cu active sites.

scholarly journals The SN2 reaction and its relationship with the Walden inversion, the Finkelstein and Menshutkin reactions together with theoretical calculations for the Finkelstein reaction

2021 ◽  
Author(s):  
Ibon Alkorta ◽  
José Elguero
Keyword(s):  
Linear Models ◽  
Theoretical Calculations ◽  
Computational Method ◽  
Basis Set ◽  
Free Energies ◽  
Nitrogen And Phosphorus ◽  
Atom Pairs ◽  
Leaving Groups ◽  
First Time ◽  
Nitrogen Phosphorus

AbstractThis communication gives an overview of the relationships between four reactions that although related were not always perceived as such: SN2, Walden, Finkelstein, and Menshutkin. Binary interactions (SN2 & Walden, SN2 & Menshutkin, SN2 & Finkelstein, Walden & Menshutkin, Walden & Finkelstein, Menshutkin & Finkelstein) were reported. Carbon, silicon, nitrogen, and phosphorus as central atoms and fluorides, chlorides, bromides, and iodides as lateral atoms were considered. Theoretical calculations provide Gibbs free energies that were analyzed with linear models to obtain the halide contributions. The M06-2x DFT computational method and the 6-311++G(d,p) basis set have been used for all atoms except for iodine where the effective core potential def2-TZVP basis set was used. Concerning the central atom pairs, carbon/silicon vs. nitrogen/phosphorus, we reported here for the first time that the effect of valence expansion was known for Si but not for P. Concerning the lateral halogen atoms, some empirical models including the interaction between F and I as entering and leaving groups explain the Gibbs free energies.

Palladium-promoted sulfur atom migration on carboranes: facile B(4)−S bond formation from mononuclear Pd-B(4) complexes

2018 ◽  
Vol 90 (4) ◽  
pp. 607-616
Author(s):  
Yin-Ping Wang ◽  
Yue-Jian Lin ◽  
Guo-Xin Jin
Keyword(s):  
Sulfur Atom ◽  
Bond Formation ◽  
Reaction Process ◽  
One Pot ◽  
Leaving Group ◽  
Atom Migration ◽  
First Time

AbstractFor the first time, carborane complexes containing a B(4)–S bond were obtained directly by heating mononuclear Pd-B(4)-bound carborane complexes. A possible mechanism involved in sulfur atom migration is presented in which the leaving group, pyridine, benzyl isocyanide or PPh3, is demonstrated to be the trigger of the reaction process. In this work, efficient routes are developed through one-pot reactions to prepare B(4)-S carborane derivatives.

Wallach rearrangement of azoxypyridines and azoxypyridine N-oxides — Charge distributions and dramatic reactivity differences

2008 ◽  
Vol 86 (4) ◽  
pp. 298-304 ◽  
Author(s):  
Erwin Buncel ◽  
Sam-Rok Keum ◽  
Srinivasan Rajagopal ◽  
Eric Kiepek ◽  
Robin A Cox
Keyword(s):  
Sulfuric Acid ◽  
Positive Charge ◽  
Theoretical Calculations ◽  
Medium Effect ◽  
Mulliken Charge ◽  
Reaction Intermediates ◽  
Charge Distributions ◽  
First Time ◽  
Acid Region

Extension of our studies of the generic Wallach rearrangement (of azoxybenzene to 4-hydroxyazobenzene) to the heteroaromatic series (azoxypyridines and axoxypyridine N-oxides) has revealed some dramatic reactivity differences, particularly for the α and β compounds. We have studied the 3-isomers and the 4-isomers in each series, each with α and β forms, eight compounds in all, in the 100 wt% sulfuric acid region of acidity. In those cases in which a product could be observed, the α and β isomers both give the same one, the corresponding 4′-hydroxyazo compounds. All the compounds react much more slowly than does azoxybenzene itself, presumably because of the extra positive charge present in the substrates, but the β isomers have half-lives of seconds and the α isomers half-lives of hundreds of hours in the 100 wt% H2SO4 acidity region. The α compounds have measurable pKBH+ values, but the β compounds do not, exhibiting only a medium effect in the acidity region in which the α compounds protonate. This means that for the β compounds, the protonated intermediates must be much less stable and the postulated reaction intermediates must be much more stable than for the α compounds. To clarify this, we have obtained Mulliken charge distributions for the various species concerned, calculating the charge carried by each half of the molecule, larger charge separations being taken to indicate lesser stability. As far as we can establish, this is the first time that this technique has been used to indicate the stabilities of carbocationic species.Key words: azoxypyridines, azoxypyridine N-oxides, Wallach rearrangement, excess acidity, basicities, theoretical calculations, charge distributions, reactivities.

scholarly journals Analysis of free and protein-bound nitrotyrosine in human plasma by a gas chromatography/mass spectrometry method that avoids nitration artifacts

2000 ◽  
Vol 345 (3) ◽  
pp. 453-458 ◽  
Author(s):  
Matthew T. FROST ◽  
Barry HALLIWELL ◽  
Kevin P. MOORE
Keyword(s):  
Reactive Nitrogen Species ◽  
Plasma Proteins ◽  
Biological Fluids ◽  
Plasma Concentrations ◽  
Normal Subjects ◽  
Gas Chromatography Mass Spectrometry ◽  
Highly Sensitive ◽  
Acidic Conditions ◽  
First Time

Measurement of nitrotyrosine in biological fluids and tissues is increasingly being used to monitor the production of reactive nitrogen species in vivo. The detection of nitrotyrosine in vivo has been reported with the use of a variety of methods including immunoassay, HPLC and GLC/MS. The validity of HPLC and immunoassays have been questioned with regard to their selectivity and sensitivity limits. In principle, the measurement of nitrotyrosine by GLC/MS permits a highly specific, highly sensitive and fully quantitative assay. The nitration of tyrosine under acidic conditions in the presence of nitrite is well documented. Derivatization for the full quantification of nitrotyrosine by using GLC/MS can lead to the artifactual nitration of tyrosine if performed under acidic conditions in the presence of nitrite. We describe a novel alkaline method for the hydrolysis and derivatization of nitrotyrosine and tyrosine, and demonstrate its applicability to the measurement of plasma concentrations of both free and protein-bound nitrotyrosine and tyrosine. A detection limit of 1 pg for nitrotyrosine and 100 pg for tyrosine has been achieved. Our method allows, for the first time, the analysis of free and protein-bound nitrotyrosine and tyrosine in biological samples. The plasma concentrations (means±S.E.M.) of free tyrosine and nitrotyrosine in eight normal subjects were 12±0.6 μg/ml and 14±0.7 ng/ml respectively. Plasma proteins contained tyrosine and nitrotyrosine at 60.7±1.7 μg/mg and 2.7±0.4 ng/mg respectively.

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