Evidence for Atropisomerism in Polycyclic γ-Butenolides: Synthesis,Scope, and Spectroscopic Studies

Design and development of a domino cyclative approach for the synthesis of new polycyclic γ-butenolides from β-aryl-Z-enoate propargylic alcohols, through the interception of an intermediate of the Z-enoate-assisted Meyer–Schuster rearrangement, has been reported. A systematic NMR analysis of various derivatives of this class revealed and supported the potential atropisomerism associated with them. These molecules represent first examples of butenolide ring-based atropisomeric compounds in organic chemistry. The synthetic process involves a synchronous construction of both rings with concurrent creation of the potential stereogenic rotational axis.     

Numerical investigation on the effect of magnetic field on natural convection heat transfer from a pair of embedded cylinders within a porous enclosure

The present work examines the influence of magnetohydrodynamic field on natural convection phenomena inside a porous square enclosure with a pair of embedded hot circular cylinders. Numerical investigations are performed to understand the effects of interspacing distance between the embedded cylinders, Hartmann number, Rayleigh number and Darcy number on the thermal transport process and the total irreversibility generation. It is observed that the isotherm distribution is strongly affected by the presence of magnetic field although the distribution of streamlines remains independent of the strength of magnetic field. This underlines the fact that magnetic field strongly influences the heat transfer process and entropy generation characteristics. It reveals that the natural convection is suppressed in the presence of a higher magnetic field as evident from the reduction in Nusselt number. It is observed that an increase in the spacing between the cylinders increases the heat transfer rate, and moreover, the effect of the magnetic field on heat transfer is more pronounced at higher interspacing distance between the embedded cylinders. The heat transfer rate increases significantly with the increase in the permeability of the medium. The entropy generation rate is independent of the strength of applied magnetic field. Further, the contribution of the entropy generation owing to friction is found to be negligible in total irreversibility obtained at lower values of Rayleigh number irrespective of Darcy number. However, the contribution of irreversibility owing to heat transfer is found to be minimal at higher values of Rayleigh number.

     

Diastereoselective Biomimetic Synthesis of Dimeric Tetrahydrocarbazoles via a Copper(II)-Catalyzed Cycloisomerization-[3+2] Cyclodimerization Cascade

The cyclodimerization (homochiral- and heterochiral−) of monomeric units for the construction of stereodefined polycyclic systems is a powerful strategy in both biosynthesis and biomimetic synthesis. Herein we have discovered and developed a Cu^II- catalyzed, biomimetic, diastereoselective tandem cycloisomerization-[3+2] cyclodimerization of 1-(indol-2-yl)pent-4-yn-3-ol. This novel strategy operates under very mild conditions, providing access to structurally unprecedented dimeric tetrahydrocarbazoles fused to a tetrahydrofuran unit in excellent yields of the products. Several fruitful control experiments, isolation of the monomeric-cycloisomerized products and their subsequent conversion into the corresponding cyclodimeric products supported their intermediacy and the possible mechanism as a cycloisomerization-diastereoselective [3+2] cyclodimerization cascade. The cyclodimerization involves a substituent controlled, highly diastereoselective homochiral [3+2] annulation or heterochiral [3+2] annulation of in situ generated 3-hydroxytetrahydrocarbazoles. The key and important features of this strategy are: a) construction of three new C−C bonds & one new C−O bond; b) creation of two new stereocenters, and c) construction of three new rings, in a single operation; d) low catalyst loading (1–5 mol %); e) 100 % atom economy; and f) rapid construction of structurally unprecedented natural product like polycyclic frameworks. A chiral pool version using an enantio- and diastereopure substrate was also demonstrated.     

PTAB mediated open air synthesis of sulfonamides,thiosulfonates and symmetrical disulfanes

A facile methodology has been described which has successfully simplified the generation of sulfonamides, thiosulfonates and symmetric disulfanes. This “trio” of reactions occur in an open air metal free atmosphere and has also been scaled up to grams making it suitable for commercialization. The reactions also have been successfully carried out with asymmetric variants, thus contributing to the chiral pool. The user friendly “trio” enables easy generation of these versatile sulfur analogues and the reaction condition employed depict an economic outline.     

Synthesis of bruguierol A employing ring closing metathesis

An expedient synthesis of bruguierol A encompassing a novel 2,3-benzo-8-oxabicyclo[3.2.1]octane ring system is described employing ring closing metathesis to generate the oxa-bridged tricyclic core.     

Nanomotors Sense Local Physicochemical Heterogeneities in Tumor Microenvironments**

The invasion of cancer is brought about by continuous interaction of malignant cells with their surrounding tissue microenvironment. Investigating the remodeling of local extracellular matrix (ECM) by invading cells can thus provide fundamental insights into the dynamics of cancer progression. In this paper, we use an active untethered nanomechanical tool, realized as magnetically driven nanomotors, to locally probe a 3D tissue culture environment. We observed that nanomotors preferentially adhere to the cancer-proximal ECM and magnitude of the adhesive force increased with cell lines of higher metastatic ability. We experimentally confirmed that sialic acid linkage specific to cancer-secreted ECM makes it differently charged, which causes this adhesion. In an assay consisting of both cancerous and non-cancerous epithelia, that mimics the in vivo histopathological milieu of a malignant breast tumor, we find that nanomotors preferentially decorate the region around the cancer cells.     

Mathematical analysis of the motion of a rigid body in a compressible Navier–Stokes–Fourier fluid

We study an initial and boundary value problem modelling the motion of a rigid body in a heat conducting gas. The solid is supposed to be a perfect thermal insulator. The gas is described by the compressible Navier–Stokes–Fourier equations, whereas the motion of the solid is governed by Newton's laws. The main results assert the existence of strong solutions, in an ‐ setting, both locally in time and globally in time for small data. The proof is essentially using the maximal regularity property of associated linear systems. This property is checked by proving the ‐sectoriality of the corresponding operators, which in turn is obtained by a perturbation method.     

A Rationally Designed Thymidine‐Based Self‐Assembled Monolayer on a Gold Electrode for Electroanalytical Applications

A self‐assembled monolayer (SAM) of 1‐(3,5‐epidithio‐2,3,5‐trideoxy‐β‐d ‐threo‐pentofuranosyl)thymine (EFT) on a gold electrode was prepared and characterized by Raman spectral and electrochemical measurements. Voltammetric and electrochemical impedance measurements show that the SAM of EFT on a Au electrode impedes the electron‐transfer reaction. The SAM of EFT was successfully used for the voltammetric sensing of urate in neutral solution. The coexisting ascorbate anion does not interfere and therefore the EFT‐based electrode was able to quantify urate at the micromolar level in the presence of a large excess amount of ascorbate. To demonstrate the practical applications, the amount of urate in two different human serum samples was quantified by using the EFT‐based electrode; the results are in good agreement with those determined by the clinical method. DFT calculations show that both ascorbate and urate have noncovalent interactions including hydrogen‐bonding interactions with EFT.     

A biomimetic type expedient approach to the tricyclic core of xyloketals. Application to a short, stereocontrolled synthesis of alboatrin and a remarkable epi to natural isomerisation

An expedient synthesis of the linear tetrahydrofurano benzopyran ring system of xyloketals is described involving an ortho ester Claisen rearrangement and an intramolecular cationic cyclisation. This strategy was applied for a short, stereocontrolled and high yield synthesis of the phytotoxic metabolite alboatrin.     

Radical-induced expeditious stereoselective synthesis of 2-alkyl 3-allyl trans-2,3-dihydrobenzofurans (TADHBs)

A thorough study on radical-induced cyclopropyl ring fragmentation with encompassed olefinic and cyclopropane environment has been performed. Interestingly, the fragmentation has occasioned onto a stereoselective synthesis of 3-allyl trans-2,3-dihydrobenzofurans with impressive yields. The trans-dihydrobenzofurans are present as central core in many molecules of medicinal interest and the present protocol deliver a straight forward access to the embedded molecular architecture.