AC Ring Research Articles

Synthesis of the ABC Core of Daphniphyllum Alkaloids with a [5-6-7] Azatricyclic Scaffold via Ring Expansion of Azabicyclic and Azatricyclic Building Blocks.

The [5-6-7] azatricyclic ABC core, found in several Daphniphyllum alkaloids, has been synthesized through a novel route involving ring expansion of a perhydroindolone to afford the AC ring system and a radical B ring closure as key steps. The level of functionalization of the reported octahydro-1,7-ethanocyclohepta[b]pyrroles suggests that they can serve as valuable building blocks in this alkaloid field. Also reported is the first synthesis of homomorphans by the ring enlargement of 2-azabicyclo[3.3.1]nonanes.

Novel architectures for power management in AC ring main system connected to electric vehicle charging station

The Domestic Photovoltaic (DPV) installation along with Domestic Energy Storage System (DESS) can play effective role in AC Ring Main Residential Distribution Network (ACRMRDN) to address the impact of Electric Vehicle (EV) charging on residential distribution network. This paper proposed two different architectures with structural changes for effective energy management in AC ring main system connected to electric charging station. The main aim of this research is to design the electric vehicle charging infrastructure in support of DPV and DESS. The effective implementation of such charging infrastructure motivate domestic consumer to play a role of prosumer. It also encourages prosumer to install independent domestic energy storage system to speedily recover installation cost of DPV and earn regular income by selling out power to electric charging stations during peak load condition. It creates win-win situation for prosumers and EV charging station to earn profit. The suggested architectures help the power system to grow individually. Such decentralization of power system reduces the impact of EV load demand and improves the reliability and stability of power system. A proposed novel architecture helps in promoting use of electric vehicle and Renewable Energy Sources (RES). On the basis of number of EVs predictions and corresponding EV load data the profit of prosumers and electric charging stations are increased to 50% and impact of EV load on the AC grid is reduced to 100%. The analysis of equivalent model of proposed architecture is done through MATLAB software.

Calculation study on complex formation of catechins with β-cyclodextrin using density function theory

The inclusion of catechins with cyclodextrin (CD) is performed for the purpose of improving the water solubility and reducing the bitterness of catechins. In this study, the effect of catechins’ conformation on the formation of an inclusion complex between catechins and β-CD was examined by density functional theory (DFT) calculation at the B3PW91/cc-pVDZ level. It is known that the main components of catechins in tea leaves are (−)-epigallocatechin (EGC), which is a non-gallate-type catechin, and (−)-epigallocatechin gallate (EGCg), which is a gallate-type catechin. Catechins have a plurality of sites that can be included by β-CD (EGC: AC ring and B ring, EGCg: AC ring, B ring, and B′ ring). First, initial models for the calculation in which each ring of catechins gradually approaches into the cavity of β-CD were built. These initial models were optimized in water and then the optimized structure of the inclusion complex in water was determined. From the results of calculation, the degree of penetration of each ring into the β-CD cavity, the complex formation energy, and the number of intermolecular hydrogen bonds were examined. The results of calculation showed that the AC ring of catechins is most deeply included in the β-CD cavity and the B′ ring of catechins forms an energetically stable complex with β-CD. It was found that the inclusion complex of catechins and β-CD is stabilized energetically by intermolecular hydrogen bonds.

Substituent effect on emission of flavonolate-boron difluoride complexes: The role of π-system for dual-state (solution and solid) emission

In a quest for the still elusive dual-state emission (DSE), i.e., intense emissions both in solution and in the solid state, the luminescence properties of novel boron difluoride complexes with flavonolates bearing substituent(s) at the B ring (R: 4-Ph (2b); 4-OPh (2c); 4-NPh2 (2d); 2,6-Me2 (2e)) have been investigated. The emission intensity and maximum wavelength are strongly influenced by the electronic and steric factors of the substituents, which are responsible for the character of the π-conjugated system over the ligand. Complexes 2b and 2c with a rigid flat π-skeleton exhibited DSE (emission quantum yield (Φ) ≥ 0.34). Complex 2d bearing a rotatable diphenylamino group showed an aggregation-induced enhanced emission (AIEE), that is strong (Φ = 0.38) in the solid state but weak (Φ = 0.13) in CH2Cl2. Thus, 2b–2d exhibited intense solid-state emissions, although the corresponding ligands presented quenched solid-state emissions. Conversely, complex 2e, in which the B ring adopted a twisted position from the fused AC ring, that is, a twisted π-system, exhibited an aggregation-caused quenching (ACQ) resulting in an intense (Φ = 0.50) and a weak (Φ = 0.02) emission in CH2Cl2 and the solid state, respectively. This work provides important insights into the role of the π-system in the changeover of emission features in dual-state.

Delocalization of the Unpaired Electron in the Quercetin Radical: Comparison of Experimental ESR Data with DFT Calculations.

In the antioxidant activity of quercetin (Q), stabilization of the energy in the quercetin radical (Q•) by delocalization of the unpaired electron (UE) in Q• is pivotal. The aim of this study is to further examine the delocalization of the UE in Q•, and to elucidate the importance of the functional groups of Q for the stabilization of the UE by combining experimentally obtained spin resonance spectroscopy (ESR) measurements with theoretical density functional theory (DFT) calculations. The ESR spectrum and DFT calculation of Q• and structurally related radicals both suggest that the UE of Q• is mostly delocalized in the B ring and partly on the AC ring. The negatively charged oxygen groups in the B ring (3′ and 4′) of Q• have an electron-donating effect that attract and stabilize the UE in the B ring. Radicals structurally related to Q• indicate that the negatively charged oxygen at 4′ has more of an effect on concentrating the UE in ring B than the negatively charged oxygen at 3′. The DFT calculation showed that an OH group at the 3-position of the AC ring is essential for concentrating the radical on the C2–C3 double bond. All these effects help to explain how the high energy of the UE is captured and a stable Q• is generated, which is pivotal in the antioxidant activity of Q.

Efficient Synthesis of the AC Ring System of Daphnilactone B

Efficient Synthesis of the AC Ring System of Daphnilactone B

Synthesis of Tricyclic Marine Alkaloids, Cylindricines, Lepadiformines, Fasicularin, and Polycitorols: A Recent Update

Cylindricines, lepadiformines, and fasicularin are tricyclic marine alkaloids bearing perhydropyrrolo- and pyrido[2,1-j] frameworks having divergent chemical functionalities. They have been isolated from marine tunicates over the last two decades and found to have a range of cytotoxicity such as DNA-alkylating ability. Recently, polycitorols have emerged as a new member of this alkaloid family. Their unique structural features and biological activities have intrigued many researchers and challenged them in their synthesis. This review describes recent syntheses of the tricyclic alkaloids based on key synthetic approaches.1 Introduction2 Total and Formal Syntheses2.1 Overview of Synthetic Strategies2.2 Azaspirocycle (BC Ring) Approaches2.3 Indolizidine (AC Ring) Approaches2.4 Azadecalin (AB Ring) Approaches2.5 Tandem Cyclization Approaches3 Summary and Future Perspective

Total Syntheses of Lepadiformine Marine Alkaloids with Enantiodivergency, Utilizing Hg(OTf)2 -Catalyzed Cycloisomerization Reaction and their Cytotoxic Activities.

The enantioselective total syntheses of lepadiformine marine alkaloids, azatricyclic natural products isolated from marine tunicates, were completed. These alkaloids have a unique chemical structure characterized by the trans-1-azadecalin (AB ring system) fused with the spirocyclic ring (AC ring system). Here we found that a cycloisomerization reaction from functionalized linear substrates to a 1-azaspiro[4.5]decane framework corresponding to the AC ring in lepadiformines is promoted by a catalytic amount of mercury(II) triflate (Hg(OTf)2 ). The total syntheses of (-)-lepadiformines A and B were achieved in 28 % and 21 % overall yields, respectively, through the novel cycloisomerization reaction. The syntheses of (+)- and (-)-lepadiformine C hydrochloride salts also enabled us to determine the absolute configuration of natural lepadiformine C. It has been found that a phenomenon of enantiodivergence occurs in lepadiformine alkaloids from a single species of marine tunicate, Clavelina moluccensis. The cytotoxic activities of synthesized lepadiformine hydrochloride salts and their synthetic intermediates were evaluated.

Total Synthesis of (-)-Lepadiformine A Utilizing Hg(OTf)2-Catalyzed Cycloisomerization Reaction.

A cytotoxic marine alkaloid (-)-lepadiformine A (1) possesses a unique structure characterized by the trans-1-azadecalin AB ring system fused with the AC spiro-cyclic ring. In this research, we found that a cycloisomerization reaction from amino ynone 2 to a 1-azaspiro[4.5]decane skeleton 3, corresponding to the AC ring system of 1, is promoted by Hg(OTf)(2). Thus, we have accomplished the efficient total synthesis of (-)-lepadiformine A in 28% overall yield by featuring the novel Hg(OTf)(2)-catalyzed cycloisomerization.

Construction of the ABC Ring System of Taxanes via Stereoselective One-Pot Three-Component Coupling and Intramolecular Alkylation of a Protected Cyanohydrin Ether

Abstract Construction of the ABC ring system of taxanes via one-pot three-component coupling and intramolecular alkylation is accomplished. The 1,4-addition of a protected cyanohydrin ether to 2-methyl-2-cyclohexenone and subsequent addition of the resulting enolate to formaldehyde proceeded stereoselectively to provide the AC ring in 90% yield. The stereoselective reduction of the 2-keto group was achieved by using hydroxy-directed hydride reduction with LiAlH4. The intramolecular alkylation of the protected cyanohydrin ether furnished the ABC ring system of taxanes in 43% yield.

Stereoselective one-pot three-component coupling approach towards the synthesis of the AC ring system of taxanes

The stereoselective one-pot three-component coupling reaction was accomplished by 1,4-addition of the protected cyanohydrin ether 9f to cyclohexenone 10g and subsequent addition of the resulting enolate to formaldehyde in high yield for the formation of the AC ring system of taxanes. We found that the bulky substituents at the 10-position in the A ring prevent the desired 1,4-addition. Similarly, the bulky trialkylsiloxy groups at the 4-position in the C ring prevent the 1,4-addition and electron-donating alkoxy groups at the same position induce the undesired retro-Michael reaction.

Prediction of Collective Characteristics for Ion Ensembles in Quadrupole Ion Traps Without Trajectory Simulations

Fundamental aspects are presented of a two-temperature moment theory for quadrupole ion traps developed via transformation of the Boltzmann equation. Solutions of the moment equations correspond to changes in the ensemble average for any function of ion velocity, because the Boltzmann equation reflects changes to an ion distribution as a whole. The function of primary interest in this paper is the ion effective temperature and its behavior during ion storage and resonance excitation. Calculations suggest that increases in ion effective temperature during resonance excitation are due primarily to power absorption from the main RF trapping field rather than from the dipolar excitation signal. The dipolar excitation signal apparently serves mainly to move ions into regions of the ion trap where the RF electric field, and thus ion RF heating, is greater than near the trap center. Both ideal and non-ideal ion trap configurations are accounted for in the moment equations by incorporating parameterized variables a and q , which are modified versions of the commonly used forms for the DC and AC ring voltages, and b and d , which are new forms that account for the voltages applied to the endcaps. Besides extending the applicability of the moment equations to non-ideal quadrupole ion traps, the modified versions of the parameterized variables can have additional utility. Calculation of the spatial dependence of ion secular oscillation frequencies is demonstrated as an example.

A Planar Catechin Analogue as a New Type of Synthetic Antioxidant

The protective role of antioxidants against free-radical associated diseases has been widely studied, leading to the development of new types of antioxidants to remove reactive oxygen species such as O2•- and •OH. We synthesized a new type of synthetic antioxidant in which the catechol (B ring) and chroman moieties (AC ring) within the (+)-catechin (CA) structure were constrained to be planar. As compared with CA, planar catechin (PCA) showed strong radical scavenging activities towards both galvinoxyl and cumylperoxyl radicals. Reduced prooxidant activity was also observed, consistent with the dianion form of PCA being weaker at generating O2•- than the dianion form of CA. PCA completely inhibited DNA-strand scission induced by the Fenton reaction, whereas CA exhibited not only antioxidant properties but also prooxidant properties consistent with enhanced DNA strand cleavage. As compared with hydrophilic CA, the lipophilicity of PCA due to its planarity may aid in penetration of these antioxidant molecules past the cell membrane. Further development of planar PCA may be a favorable approach towards new clinically useful antioxidants for the treatment of free-radical associated diseases.

Synthesis of the AC Ring of Paclitaxel: Formation of the C Ring by [3 + 2] Cycloaddition with a Preformed A Ring.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of the AC Ring of Paclitaxel: Formation of the C Ring by [3+2] Cycloaddition with a Preformed A Ring

The stereoselective formation of the C ring was accomplished by nitrile oxide [3+2] cycloaddition of an intermediate with the A ring already constructed. We found that stereoelectronic effect to a 1,1-substituted alkene moiety is important in the reaction.

Spintronic Faraday rotation spectroscopy and geometrical modulation of spin current in an Aharonov-Casher ring

We study the ballistic spin transmission through an AC ring between two ferromagnetic filter-electrodes in the presence of spin-orbit interaction, theoretically. It is shown that the spin precession of polarized electrons can be controlled via a cylindrically symmetric electric field, and the sequence of the polarized conductance depends on the relative orientation of magnetization between the left and right filters. The injected spin-polarized electrons can be blocked completely for the special values of electric field and angle of texture, which makes the magnetoresistance to be drastically enhanced. We also propose an interference scheme to detect the geometric phase.

Design, synthesis and biochemical evaluation of AC ring mimics as novel inhibitors of the enzyme estrone sulfatase (ES)

We report the results of our study into a series of 4′- O-sulfamoyl-4-biphenyl based compounds as novel inhibitors of the enzyme estrone sulfatase (ES). From the results of the molecular modeling design process, it was suggested that these compounds would be able to mimic both the A and C rings of the steroid backbone, and thus possess inhibitory activity against ES. The results of the biochemical evaluation study show that these compounds are indeed good inhibitors, possessing greater inhibitory activity than COUMATE, but weaker inhibitory activity than EMATE or the tricyclic derivative of COUMATE, namely 667-COUMATE. Furthermore, the compounds are observed to be irreversible inhibitors.

Logic circuits based on carbon nanotubes

We demonstrate logic circuits with field-effect transistors based on single carbon nanotubes. A new technique is used for achieving local gates in nanotube field-effect transistors that provide excellent capacitive coupling between the gate and nanotube, enabling the transistor to be ambipolar. The transistors show favorable device characteristics such as a high gain, a large on-off ratio, and room-temperature operation. Importantly, it also allows for the integration of multiple devices on a single chip. Indeed, we demonstrate 1-, 2-, and 3-transistor circuits that exhibit a wide range of digital logic operations such as an inverter, a logic NOR, and an AC ring oscillator.

Design, Synthesis and Biochemical Evaluation of AC Ring Mimics as Novel Inhibitors of the Enzyme Estrone Sulfatase (ES).

AbstractFor Abstract see ChemInform Abstract in Full Text.

Design, synthesis and biochemical evaluation of aC ring mimics as novel inhibitors of the enzyme estrone sulfatase (ES)

We report the initial results of our study into a series of simple 4′- O-sulfamoyl-4-biphenyl based compounds as novel inhibitors of the enzyme estrone sulfatase (ES). The results of the study show that these compounds are potent inhibitors, possessing greater inhibitory activity than COUMATE, but weaker inhibitory activity than EMATE or the tricyclic derivative of COUMATE, namely 667-COUMATE. Furthermore, the compounds are observed to be irreversible inhibitors.