This communication describes a simple solvent-free method for fabricating chemoresistive gas sensors on the surface of paper. The method involves mechanical abrasion of compressed powders of sensing materials on the fibers of cellulose. We illustrate this approach by depositing conductive layers of several forms of carbon (e.g., single-walled carbon nanotubes [SWCNTs], multi-walled carbon nanotubes, and graphite) on the surface of different papers (Figure 1, Figure S1). The resulting sensors based on SWCNTs are capable of detecting NH3 gas at concentrations as low as 0.5 part-per-million.
ammonia; carbon nanotubes; mechanical abrasion; sensors; paper
Alzheimer’s Disease; β-Secretase; FRET; Imaging agents; Analytical Methods
boron; heterocycles; matrix isolation; benzene; density functional calculations
From the 19th century to the present, the complex indole alkaloid strychnine has engaged the chemical community. In this review, we examine why strychnine has been and remains today an important target for directed synthesis efforts. A selection of the diverse syntheses of strychnine is discussed with the aim of identifying their influence on the evolution of the strategy and tactics of organic synthesis.
natural products; strychnine; synthesis strategy; total synthesis
Genetic incorporation of a cyclopropene amino acid, Nε-(1-methylcycloprop-2-enecarboxamido)-lysine (CpK), into sperm whale myoglobin site-specifically in E. coli as well as enhanced green fluorescent protein in mammalian cells was achieved through amber codon suppression employing an orthogonal aminoacyl-tRNA synthetase/tRNACUA pair. Because of its high ring strain, cyclopropene exhibited fast reaction kinetics (up to 58 ± 16 M−1 s−1) in the photoclick reaction and allowed rapid (~ 2 min) bioorthogonal labeling of proteins in mammalian cells.
alkene; cyclopropene; tetrazole; bioorthogonal; proteins
A palladium-catalyzed reaction is presented for the synthesis of highly substituted indoles involving three independent components in a one-pot reaction. Two distinct palladium catalyzed coupling reactions occur using a single catalytic system: a Buchwald-Hartwig reaction and an arene-alkene coupling. Quantum chemical computations provide insight into the mechanism of the latter coupling step.
indole methodology; multicomponent; palladium catalysis
Sweet to the Core Enantioselective formal total syntheses of the Stemona alkaloids didehydrostemofoline and isodidehydrostemofoline were accomplished in 24 steps from commercially available 2-deoxy-d-ribose. The synthesis features a novel cascade of reactions culminating in an intramolecular dipolar cycloaddition to form the cage-like, tricyclic core of the stemofoline alkaloids from an acyclic diazo imine intermediate.
cascade reaction; stemofoline alkaloids; enantioselective; total synthesis; azomethine ylide; dipolar cycloaddition
Shine and rise! GABAA–receptors are ligand-gated chloride channels that respond to the major inhibitory neurotransmitter of the mammalian central nervous system. Herein, we introduce azobenzene derivatives of propofol that increase GABA-induced currents when irradiated with light and thus function as photochromic potentiators. One of our molecules, AP2, can be employed as a light-dependent general anesthetic in translucent tadpoles.
propofol; azobenzenes; GABA receptors; photopharmacology
The chemoselective and complementary Pd-and Cu-catalyzed N-arylation of 2-aminobenzimidazoles is described. Selective N-arylation of the amino-group was achieved with a Pd-catalyzed method, while selective N-arylation of azole nitrogen was achieved with a Cu-catalyzed procedure. The utility of these complementary sets of conditions is demonstrated in several two-step, selective syntheses of di-arylated aminoazoles.
palladium; copper; C-N coupling; aminoazole; N-arylation
Hip to be square: Styrenes participate in [2+2] cycloadditions upon irradiation with visible light in the presence of an iridium(III) polypyridyl complex. In contrast to previous reports of visible light photoredox catalysis, the mechanism of this process involves photosensitization by energy transfer and not electron transfer.
cycloaddition; cyclobutanes; energy transfer; photocatalysis; visible light
Resonance Raman spectroscopy is used to document, for the first time, a 6 cm−1 decrease of the Fe-S stretch by introducing an H-bond donor into the proximal pocket of a cytochrome P450, which interacts with the key cysteine thiolate axial ligand. The anticipated trans-effect on bound exogenous ligands is also confirmed and evidence is obtained supporting intimate interaction of the new histidyl-imidazole fragment with the heme periphery.
biophysics; heme proteins; oxidoreductases; Raman spectroscopy
The highly complex structure of syndecan-1 heparan sulfate glycopeptide was successfully assembled. The protective groups utilized and sequences for glycosyl linkage formation and protective group removal are critical for the success of synthesis. This is the first time this type of sulfated glycopeptides has been prepared, which lays the foundation to access other members of this important class of molecules.
glycopeptides; glycosylation; synthetic design; sulfation; total synthesis
copper; enantioselective catalysis; homopropargyl amines; N-heterocyclic carbenes; propargyl additions
DNA delivery; endocytosis; gene therapy; gold nanoparticles; ligands (organic)
post-translational modification; histone; crotonylation; unnatural amino acid; site-specific incorporation
A catalyst composed of Pd2(dba)3 and (S)-Siphos-PE is effective for the enantioselective coupling of N-allyureas with aryl bromides to afford 4-substituted imidazolidin-2-ones with up to 95% ee. Added water leads to significantly improved enantioselectivities with electron-poor aryl halide substrates. The mechanism of these transformations is discussed, and evidence is presented which suggests that, in contrast to other asymmetric alkene carboaminations, C–C bond-forming reductive elimination is the enantiodetermining step of these reactions.
Asymmetric Catalysis; Asymmetric Synthesis; Heterocycles; Palladium; Stereoselective
A versatile reaction cascade triggered by Rh(II)-catalyzed diazo decomposition followed by a vinylogous N-H insertion/Lewis acid catalyzed Mannich addition that produces highly substituted 1,2,3,6-tetrahydropyridazines in up to 97% ee with high yield and diastereocontrol has been developed.
Asymmetric Catalysis; Tetrahydropyridazines; Enantioselective; Vinylogous N-H Insertion; Cycloaddition; Rhodium
Lithiation; Fragment-coupling; Diastereoselectivity; Terpenoids; Fused-ring Systems; DFT Calculations
total synthesis; natural products; terpenoids; structure determination; asymmetric catalysis; allylation; ring contraction; rearrangement; cycloaddition; palladium; nickel
Radicals; Photoredox; Fragment-coupling; Total synthesis; Terpenoids; Fused-ring Systems
Indoles: A joint effort of light and air We have developed a mild aerobic oxidation protocol using visible light photocatalysis to synthesize structurally diverse N-arylindoles. The procedure employs 4 mol% [Ru(bpz)3](PF6)2, 18W LED light, and is performed open to the atmosphere. Readily prepared o-stryryl anilines are converted to a variety of indoles via a cascade sequence composed of oxidation of anilines, C-N bond formation, and aromatization. A 1,2-carbon shift can be also incorporated into this cascade event to further extend the substrate scope of the method. bpz = 2, 2′-Bipyrazine
cascade; indole; photocatalysis; ruthenium; visible light