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.

Concise Synthesis of the ABC-Ring System of the Azafluoranthene, Tropoisoquinoline and Proaporphine Alkaloids: An Olefin Hydroacylation/Pomeranz–Fritsch Cyclization Approach

A straightforward approach toward a decorated cyclopenta[ij]isoquinoline embodying the ABC-ring system characteristic of the azafluoranthene (triclisine), tropoisoquinoline (pareitropone) and proaporphine (prodensiflorin B) alkaloids, is reported. The synthetic ­sequence entailed a novel 40% KF/Al2O3-mediated hydroacylation of a 2-allyl-benzaldehyde derivative, obtained in two steps from isovanillin, through O-allylation and Claisen rearrangement to assemble the AC-ring system. This was followed by an O-methylation and a reductive ­amination of the resulting indanone with aminoacetal. A modified Pomeranz–Fritsch cyclization was next implemented to install ring B, through sulfonamidation, followed by acid-promoted cyclization and ­final desulfonylation in situ.

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

AC Ring Distribution: Architecture for Subsea Power Distribution

Subsea power transmission and distribution is an emerging technology that may enable the oil and gas industry to produce hydrocarbon reserves in deeper and more remote offshore waters. The longer tieback subsea operations will likely require pumps and compressors driven by electric motors to be located on the sea floor to pressure boost the oil and gas to surface and/or onshore platforms. Existing HVAC and HVDC technologies are efficient means for subsea power transmission and distribution. However, they are subject to a variety of limitations, for instance, the single-point failures that would impact production uptime. Furthermore, it is challenging to implement subsea bulk power transmission and distribution by using existing architectures due to the footprint, weight and electrical insulation requirements. This paper describes a subsea power distribution architecture — AC ring. It can be used to interface a high-voltage bulk power transmission network, either AC or DC, to a subsea multi-load AC system. The new topology uses series-connected, by-passable, open-winding transformers to provide better modular design flexibility. The system is expected to be more reliable than conventional “hub and spoke” architectures and more technically feasible regarding practical subsea equipment designs.