Fe(III)-Catalyzed Bicyclization of Yne-Allenones With Indoles for the Atom-Economic Synthesis of 3-Indolyl Cyclobutarenes

A new Fe(III)-catalyzed bicyclization reaction of yne-allenones with indoles has been established, enabling the direct construction of cyclobuta[a]naphthalen-4-ols with an all-carbon quaternary center in good to excellent yields. This reaction was performed by using low-cost FeCl3 as the catalyst and EtOH as the environmentally benign solvent, providing a green protocol for constructing the cyclobutarene framework with a high degree of atom economy and functional group compatibility. The reaction mechanism was proposed to proceed through a [2 + 2] cycloaddition/1,6-conjugate addition cascade

Cobalt-catalysed site-selective intra- and intermolecular dehydrogenative amination of unactivated sp3 carbons

Cobalt-catalysed sp2 C–H bond functionalization has attracted considerable attention in recent years because of the low cost of cobalt complexes and interesting modes of action in the process. In comparison, much less efforts have been devoted to the sp3 carbons. Here we report the cobalt-catalysed site-selective dehydrogenative cyclization of aliphatic amides via a C–H bond functionalization process on unactivated sp3 carbons with the assistance of a bidentate directing group. This method provides a straightforward synthesis of monocyclic and spiro β- or γ-lactams with good to excellent stereoselectivity and functional group tolerance. In addition, a new procedure has been developed to selectively remove the directing group, which enables the synthesis of free β- or γ-lactam compounds. Furthermore, the first cobalt-catalysed intermolecular dehydrogenative amination of unactivated sp3 carbons is also realized., Functionalizing unactivated carbon–hydrogen bonds is challenging, especially when using non-precious metals and dealing with sp3 hybridized carbons. Here, the authors report an intramolecular cobalt catalysed amination of C–H bonds of sp3 carbons, giving access to β- and γ-lactams

Construction of a bacterial autoinducer detection system in mammalian cells

Quorum sensing (QS) is a cell density-dependent signaling system used by bacteria to coordinate gene expression within a population. QS systems in Gram negative bacteria consist of transcription factors of the LuxR family and their acyl homoserine lactone (AHL) ligands. We describe here a method for examining QS signaling systems in mammalian cells that uses engineered LuxR-type proteins from the opportunistic pathogen, Pseudomonas aeruginosa, which can function as AHL-dependent transcription factors. The engineered proteins respond to their cognate ligands and display sequence specific DNA binding properties. This system has several potential biotechnological and biological applications. It may be used to characterize any LuxR-type protein, screen animal and plant cell extracts or exudates for compounds that mimic or interfere with AHL signaling or to screen different cell types for AHL inactivating activities

Light-activated ferroelectric transition in layer dependent Bi2O2Se films

Bi2O2Se has attracted intensive attention due to its potential in electronics, optoelectronics, as well as ferroelectric applications. Despite that, there have only been a handful of experimental studies based on ultrafast spectroscopy to elucidate the carrier dynamics in Bi2O2Se thin films, Different groups have reported various ultrafast timescales and associated mechanisms across films of different thicknesses. A comprehensive understanding in relation to thickness and fluence is still lacking. In this work, we have systematically explored the thickness-dependent Raman spectroscopy and ultrafast carrier dynamics in chemical vapor deposition (CVD)-grown Bi2O2Se thin films on mica substrate with thicknesses varying from 22.44 nm down to 4.62 nm at both low and high pump fluence regions. Combining the thickness dependence and fluence dependence of the slow decay time, we demonstrate a ferroelectric transition in the thinner (< 8 nm) Bi2O2Se films, influenced by substrate-induced compressive strain and non-equilibrium states. Moreover, this transition can be manifested under highly non-equilibrium states. Our results deepen the understanding of the interplay between the ferroelectric phase and semiconducting characteristics of Bi2O2Se thin films, providing a new route to manipulate the ferroelectric transition

Four-layer folding framework: design, GAP synthesis, and aggregation-induced emission

The design and synthesis of a type of [1 + 4 + 2] four-layer framework have been conducted by taking advantage of Suzuki–Miyaura cross-coupling and group-assisted purification (GAP) chemistry. The optimized coupling of double-layer diboronic esters with 1-bromo-naphth-2-yl phosphine oxides resulted in a series of multilayer folding targets, showing a broad scope of substrates and moderate to excellent yields. The final products were purified using group-assisted purification chemistry/technology, achieved simply by washing crude products with 95% EtOH without the use of chromatography and recrystallization. The structures were fully characterized and assigned by performing X-ray crystallographic analysis. UV–vis absorption, photoluminescence (PL), and aggregation-induced emission (AIE) were studied for the resulting multilayer folding products

Role of SAM Chain Length in Enhancing the Sensitivity of Nanopillar Modified Electrodes for Glucose Detection

In this report, alkanethiol self assembled monolayers (SAM) with two different chain lengths were used to immobilize the functionalizing enzyme (glucose oxidase) onto gold nanopillar modified electrodes and the electrochemical processes of these functionalized electrodes in glucose detection were investigated. First, the formation of these SAMs on the nanopillar modified electrodes was characterized by the cyclic voltammetry and electrochemical impedance spectroscopy techniques, and then the detection sensitivity of these functionalized electrodes to glucose was evaluated by the amperometry technique. Results showed that the SAM of alkanethiols with a longer chain length resulted in a higher degree of surface coverage with less defect and a higher electron transfer resistance, whereas the SAM of alkanethiols with a shorter chain length gave rise to a higher detection sensitivity to glucose. This study sheds some new insight into how to enhance the sensing performance of nanopillar modified electrodes

Asymmetric synthesis of unusual amino acids for peptide molecular design and molecular recognition studies.

Asymmetric synthetic organic chemistry of amino acids is of fundamental importance for the study of peptide and protein molecular design and molecular recognition. The designed unusual amino acids can provide unique conformational and topographical properties that are crucial for molecular recognition processes between peptide ligands and specific receptors, receptor subtypes, and the related signal transduction processes. It is necessary to design and synthesize optically pure unusual amino acids to meet different stereochemical requirements for different receptors and the various active sites on receptors. The Evans-type auxiliary has played an important role in the asymmetric synthesis of optically pure amino acids in the past decade. However, a lot of theoretical and practical research aspects in this field which are related to sensitive chiral enolates, new methodologies and new synthetic procedures need to be investigated. This thesis will present some new tactics for peptide molecular design, for asymmetric synthesis of β-branched α-amino acids and for the related mechanistic organic chemistry which include: a one-pot tandem Michael-like addition/electrophilic bromination reaction and its application to the total asymmetric synthesis of four individual four individual isomers of 2', β-di-methyl tyrosine; an efficient mono- and di-demethylation procedure for aryl-methyl ethers of unusual amino acids; 1,2-asymmetric cis electrophilic induction in allylic-strained boron enolates and its potential application for the asymmetric synthesis of unusual amino acids; a new strategy for the total synthesis of the four individual isomers of β-methylphenylalanine by using 4-phenyl-oxazolidinone as a new chiral resolution reagent and simultaneously as a chiral auxiliary which can provide complete stereoselectivities; a concise method to separate racemic Boc-amino acids, including Boc-unusual amino acids, and a new chiral resolution reagent for HPLC and NMR analysis; a mechanistic study of the asymmetric Michael-like addition reaction by using 4-phenyl-oxazolidinone as a chemical probe (and a potential probe to study biological processes in the future when this motif is incorporated into biologically active molecules). In the last part of the thesis, a new method for the synthesis of the peptide Biphalin, which is perhaps the most potent antinociceptive molecule examined thus far, by solution phase procedures which greatly accelerates the synthetic process and the structure-activity relationships study of Biphalin from the new uses of β-constrained unusual amino acids. Finally, some new strategies for peptide molecular design are discussed

Group-assisted purification (GAP) chemistry for the synthesis of Velcade via asymmetric borylation of N-phosphinylimines

The authors acknowledge the financial support from the NIH (R33DA031860), the Robert A. Welch Foundation (D-1361) and the Jiangsu Innovation Team Program (P. R. China) for their support of this research. They also thank NSF Grant CHE-1048553 and the CRIF program for supporting their NMR facility.A new approach to the anticancer drug Velcade was developed by performing asymmetric borylation of an imine anchored with a chiral N-phosphinyl auxiliary. Throughout the 7-step synthesis, especially in the imine's synthesis and in the asymmetric borylation reactions, operations and work-up were conducted in simple and easy ways without any column chromatographic purification, which defines the GAP (group-assisted purification) chemistry concept. It was found that the optically pure isomer (dr > 99: 1) can be readily obtained by washing the crude mixture of the asymmetric borylation reaction with hexane; the chiral N-phosphinyl auxiliary can be easily recovered after deprotection is finished. Several other N-phosphinylimines were also investigated for the asymmetric borylation reaction. The absolute configuration of the borylation product was confirmed by single crystal X-ray diffraction analysis.Publisher PDFPeer reviewe