Synthesis of pyrrolidine-based hamamelitannin analogues as quorum sensing inhibitors in Staphylococcus aureus

• Jakob Bouton,
• Kristof Van Hecke,
• Reuven Rasooly and
• Serge Van Calenbergh

Beilstein J. Org. Chem. 2018, 14, 2822–2828, doi:10.3762/bjoc.14.260

• which the cationic character of the pyrrolidine nitrogen is removed, were also synthesized. The correct stereochemistry of the synthesized analogues was unequivocally proven via X-ray structural analysis of compound 3a (Figure 2). Biological evaluation The synthesized analogues were tested in a S

Learning from B₁₂ enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

• Keishiro Tahara,
• Ling Pan,
• Toshikazu Ono and
• Yoshio Hisaeda

Beilstein J. Org. Chem. 2018, 14, 2553–2567, doi:10.3762/bjoc.14.232

• carboxylic ester-migrated product was formed via not a radical, but a cationic intermediate that was generated by the fragmentation to the monoalkylated complex at the anode (Scheme 2). 2-2. Artificial enzyme-mediated reactions A vesicle-type B12 artificial enzyme was constructed by combining bilayer

Synthesis of aryl sulfides via radical–radical cross coupling of electron-rich arenes using visible light photoredox catalysis

• Amrita Das,
• Mitasree Maity,
• Simon Malcherek,
• Burkhard König and
• Julia Rehbein

Beilstein J. Org. Chem. 2018, 14, 2520–2528, doi:10.3762/bjoc.14.228

• photocatalyst and complete the catalytic cycle forming the sulfate dianion 5 and sulfate radical anion 6. The phenyl sulfide radical 2 formed upon homolytic cleavage of diphenyl disulfide adds to the radical cation of the arene to form the unstable cationic intermediate 3. Aromatization by deprotonation leads

A challenging redox neutral Cp*Co(III)-catalysed alkylation of acetanilides with 3-buten-2-one: synthesis and key insights into the mechanism through DFT calculations

• Andrew Kenny,
• Alba Pisarello,
• Arron Bird,
• Paula G. Chirila,
• Alex Hamilton and
• Christopher J. Whiteoak

Beilstein J. Org. Chem. 2018, 14, 2366–2374, doi:10.3762/bjoc.14.212

• calculated but proved to be less favourable than the initial tautomerization. Protonation of the unsaturated β-carbon position formed the highly stable Int 5, which dissociates to form the observed product and regenerate the cationic active catalyst species [Cp*Co(III)OAc]+. The less than 0.5 kcal mol−1

• pathway for Cp*Co(III)-catalysed alkylation of acetanilide with 3-buten-2-one obtained from DFT studies; Int A is the direct interaction between the cationic [Cp*Co(III)AcO]+ species and the 3-buten-2-one coupling partner. Comparison between energies during the Cp*Co(III)-catalysed coupling of 3-buten-2

• -one with acetanilide (black line) and benzamide (blue line); RS 1 is the direct interaction between the cationic [Cp*Co(III)AcO]+ species and the 3-buten-2-one coupling partner and RS 2 is the interaction of the metallocycle intermediate with a second acetanilide. Comparative visualisation of bcp for

Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• tolerance toward a variety of functionalities on arenes as well as alkynes. The isolated cationic cobalt intermediate (C3) and the mechanistic studies strongly indicate that the reaction proceeds through C–H activation via concerted metallation-deprotonation (CMD) to form cobaltacycle C1. Subsequently

Dynamic light scattering studies of the effects of salts on the diffusivity of cationic and anionic cavitands

• Anthony Wishard and
• Bruce C. Gibb

Beilstein J. Org. Chem. 2018, 14, 2212–2219, doi:10.3762/bjoc.14.195

• these cases aggregation of host 2 also exhibited a cationic dependence, with an observed trend Na+ > Li+ > K+ ≈ Cs+. In combination, these results reveal new details of specific ion pairings in aqueous solution and how this can influence the properties of dissolved organics. Keywords: cavitand; dynamic

• akin to how these anions can partially unfold proteins. Alternatively, poorly solvated anions can also associate closely with cationic groups, induce charge neutralization, and engender aggregation and/or precipitation. In other words, they can also cause an apparent increase in the hydrophobic effect

• aggregation of cationic 2: namely Na+ > Li+ > K+ ≈ Cs+. This cation effect must be indirect. If the counter ions of 2 (Cl−) are viewed as non-coordinating, this phenomenon can be interpreted as arising from a simple competition between the two “hosts” 2 and M+ (Scheme 1). In such a system, I− can only

Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules

• Hendrik V. Schröder and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2018, 14, 2163–2185, doi:10.3762/bjoc.14.190

• molecular switch. A first one-electron oxidation [23] converts neutral TTF (1) into the radical-cationic species 1●+ (Figure 1). The TTF radical cation is one of the rare organic radicals that are long-term stable and even isolable. A second oxidation step yields the dication 12+. Both redox-transitions are

• -cationic form since the association energy of the donor–acceptor complex must be overcome. After oxidation, the radical-cation 1●+ is expelled from host 3 by repulsive Coulombic forces. If 1●+ gets further oxidized to the π-electron-poor dication 12+, the π-electron-rich macrocycle 8 can now encapsulate

D-Fructose-based spiro-fused PHOX ligands: synthesis and application in enantioselective allylic alkylation

• Michael R. Imrich,
• Jochen Kraft,
• Cäcilia Maichle-Mössmer and
• Thomas Ziegler

Beilstein J. Org. Chem. 2018, 14, 2082–2089, doi:10.3762/bjoc.14.182

• charge in 9c this oxocarbenium ion is more stable compared to 9b. Cyclic oxocarbenium ions of the type of 9c are known to be stable intermediates which can even be isolated in the absence of nucleophiles [45][46][47]. Due to the higher stability of the cationic intermediate the nucleophilic attack of the

Synthesis of new p-tert-butylcalix[4]arene-based polyammonium triazolyl amphiphiles and their binding with nucleoside phosphates

• Vladimir A. Burilov,
• Guzaliya A. Fatikhova,
• Mariya N. Dokuchaeva,
• Ramil I. Nugmanov,
• Diana A. Mironova,
• Pavel V. Dorovatovskii,
• Victor N. Khrustalev,
• Svetlana E. Solovieva and
• Igor S. Antipin

Beilstein J. Org. Chem. 2018, 14, 1980–1993, doi:10.3762/bjoc.14.173

• surfactants having a host–guest recognition site [23]. So, they are able to form nanoaggregates in aqueous solutions, thus providing the concentration of the active binding sites into nanoaggregate for multivalent binding with the substrate [24]. We recently synthesized a series of cationic receptors based on

• the p-tert-butylthiacalix[4]arene platform with 1,3-alternate conformation having polyammonium binding sites. They were shown to effectively interact with calf thymus DNA causing a 4-fold compaction of the latter [25]. Related macrocycles containing two cationic imidazolium fragments demonstrated a

• diacetylene surfactant matrix by amphiphilic receptors with subsequent photopolymerization is a commonly used approach for the design of colorimetric analytical devices [50]. Taking into account the cationic nature of the synthesized calixarene macrocycles, the amido-diacetylene lipid bearing a terminal amino

Cationic cobalt-catalyzed [1,3]-rearrangement of N-alkoxycarbonyloxyanilines

• Itaru Nakamura,
• Mao Owada,
• Takeru Jo and
• Masahiro Terada

Beilstein J. Org. Chem. 2018, 14, 1972–1979, doi:10.3762/bjoc.14.172

• , Aoba-ku, Sendai 980-8578 Japan 10.3762/bjoc.14.172 Abstract A cationic cobalt catalyst efficiently promoted the reaction of N-alkoxycarbonyloxyanilines at 30 °C, affording the corresponding ortho-aminophenols in good to high yields. As reported previously, our mechanistic studies including oxygen-18

• reaction conditions with high functional group tolerance. Based on this concept, we disclosed that cationic cobalt catalysts efficiently promote the reaction of O-alkoxylcarbonyl-N-arylhydroxylamines 1 at 30 °C, affording the corresponding 2-aminophenol derivatives 2 in good to high yields [13]. Our

• 2-aminophenol derivative 2a (Table 1, entries 3 and 4). Moreover, a cationic copper catalyst generated from CuCl2 and two equivalents of AgSbF6 was effective to afford 2a in good yield (Table 1, entry 5), even at 30 °C (Table 1, entry 8). The use of a ligand, such as 1,10-phenanthroline (phen) and

Rational design of boron-dipyrromethene (BODIPY) reporter dyes for cucurbit[7]uril

• Mohammad A. Alnajjar,
• Jürgen Bartelmeß,
• Robert Hein,
• Pichandi Ashokkumar,
• Mohamed Nilam,
• Werner M. Nau,
• Knut Rurack and
• Andreas Hennig

Beilstein J. Org. Chem. 2018, 14, 1961–1971, doi:10.3762/bjoc.14.171

• transfer; supramolecular chemistry; Introduction Cucurbit[n]urils (CBn, n = 5–8, 10, and 14) are a class of macrocyclic host molecules which are water soluble, nontoxic, and are able to bind a large variety of neutral and cationic guests in their inner cavity with high affinity [1][2][3][4]. This unique

An amphiphilic pseudo[1]catenane: neutral guest-induced clouding point change

• Tomoki Ogoshi,
• Tomohiro Akutsu and
• Tada-aki Yamagishi

Beilstein J. Org. Chem. 2018, 14, 1937–1943, doi:10.3762/bjoc.14.167

• in the clouding point. The clouding point of 1 increased upon addition of a cationic guest as the hydrophilic ratio in the molecule increased by formation of the complex with the hydrophilic cationic guest [5]. We also demonstrated photoresponsive LCST behavior by using a photoresponsive host–guest

• complex system between amphiphilic pillar[6]arene 2 and a photoresponsive cationic azobenzene guest [6]. However, neutral guest molecules could not induce a clear LCST change because encapsulation of the neutral guest in the hydrophobic pillar[n]arene core did not significantly change the hydrophobic

Synthesis of 9-arylalkynyl- and 9-aryl-substituted benzo[b]quinolizinium derivatives by Palladium-mediated cross-coupling reactions

• Siva Sankar Murthy Bandaru,
• Darinka Dzubiel,
• Heiko Ihmels,
• Mohebodin Karbasiyoun,
• Mohamed M. A. Mahmoud and
• Carola Schulzke

Beilstein J. Org. Chem. 2018, 14, 1871–1884, doi:10.3762/bjoc.14.161

• ligands; fluorescence; heterocycles; Pd-mediated couling reactions; quinolizinium; Introduction Polycyclic cationic hetarenes are a paradigm of DNA-binding ligands whose association with the nucleic acid may affect the biological activities of the DNA [1][2][3][4]. For example, a DNA-bound heterocyclic

• [14][15][16][17][18] and whose interaction with the nucleic acid may be used for fluorimetric detection of the latter [19][20]. To further exploit the DNA-binding properties of this specific class of cationic hetarenes, synthetic routes to novel derivatives with the desired substitution pattern and

• the nucleophile at the 6-position of the substrate and subsequent ring-opening reaction [37][38]. Considering this impediment and the additional difficulties that may occur during purification of these cationic hetarenes the reaction and work-up conditions of Pd-mediated coupling reactions of benzo[b

Water-soluble SNS cationic palladium(II) complexes and their Suzuki–Miyaura cross-coupling reactions in aqueous medium

• Alphonse Fiebor,
• Richard Tia,
• Banothile C. E. Makhubela and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1859–1870, doi:10.3762/bjoc.14.160

• their SCS analogues, SNS pincer complexes are poorly studied for their use in coupling reactions. Accordingly, a series of water soluble cationic Pd(II) SNS pincer complexes have been successfully synthesised and investigated in detail for their catalytic activity in Suzuki–Miyaura coupling reactions

• investigation of the mechanism of the reaction revealed that a Pd(II) to Pd(IV) route is the more likely pathway which was further supported by computational studies. Keywords: cationic palladium(II) complexes; Pd(II)/Pd(IV) complexes; SNS pincer complexes; Suzuki–Miyaura; Introduction The Suzuki–Miyaura C–C

• coupling partners. Encouraged by the high hydrophilicity and the potential activity of such complexes, we are interested in the synthesis of cationic palladium(II) SNS pincer complexes of the general structure 17 (Figure 2b) having rigid fused cyclic rings imparted by a pyridine backbone; and systematic

Synthesis of new tricyclic 5,6-dihydro-4H-benzo[b][1,2,4]triazolo[1,5-d][1,4]diazepine derivatives by [3⁺ + 2]-cycloaddition/rearrangement reactions

• Lin-bo Luan,
• Zi-jie Song,
• Zhi-ming Li and
• Quan-rui Wang

Beilstein J. Org. Chem. 2018, 14, 1826–1833, doi:10.3762/bjoc.14.155

• + + 2]-cycloaddition, α-acetoxyazo intermediates are initially transformed into an azocarbenium ion. Subsequently, it takes part in a cationic cycloaddition reaction with the triple bond of a nitrile followed by a rearrangement reaction [35][36][37][38][39]. This type of ionic cycloaddition

• , we wish to describe the synthesis of unprecedented tricyclic heterocycles, i.e., 5,6-dihydro-4H-benzo[b][1,2,4]triazolo[1,5-d][1,4]diazepinium salts 10 and the related neutral free base derivatives 13 via the cationic [3+ + 2]-cycloaddition/rearrangement reactions using the bicyclic 4-acetoxy-4-azo

• electron-withdrawing N-acetyl functionality in compounds 8 was introduced to conceal the basicity of the N(1) atom, thus avoiding the plausible disturbance in the following cationic polar cycloaddition/rearrangement reaction. After the accomplishment of the synthesis of key intermediates 8, we tried to

Recent advances in hypervalent iodine(III)-catalyzed functionalization of alkenes

• Xiang Li,
• Pinhong Chen and
• Guosheng Liu

Beilstein J. Org. Chem. 2018, 14, 1813–1825, doi:10.3762/bjoc.14.154

• enantioselectivity (52 vs 53). Moreover, the more electron-deficient 3,4,5-trifluorophenyl analog 54 was found to be less enantioselective. The authors proposed that the benzylic groups can stabilize the cationic intermediates and/or transition states through cation–π interactions, which play an important role in

Design, synthesis and structure of novel G-2 melamine-based dendrimers incorporating 4-(n-octyloxy)aniline as a peripheral unit

• Cristina Morar,
• Pedro Lameiras,
• Attila Bende,
• Gabriel Katona,
• Emese Gál and
• Mircea Darabantu

Beilstein J. Org. Chem. 2018, 14, 1704–1722, doi:10.3762/bjoc.14.145

• aliphatic carboxyl group ionisation thus promoting 1H shielding of proximal (α and β) methylene protons, was reported in the case of some G-2 PAMAM ionic dendrimers obtained by –COOH/H2N– neutralisation (NMR solvent, CDCl3) [63]. However, in the case of the cationic counterpart, if a more illustrative

• protonated site in ionic dendrimers 7b, 8 and 9 could not be attributed accurately either in solution (1H NMR), or in the solid state (IR). Consequently, their proposed cationic structures shown in Figure 1 and Scheme 4 (linker P-1 as piperazin-1-ium moiety) should be seen intuitively, a proton sponge-like

• 7b, presumably due to the sterically induced imperfect accommodation of the three G-1 cationic dendrons D-N

  NH2+ around the smallest central tris-anion of the series, trimesic tris-carboxylate. In other words, the 2D-1H-DOSY NMR charts were consistent with the envisaged 3(D-N

  NH):1 (trimesic acid

Natural and redesigned wasp venom peptides with selective antitumoral activity

• Marcelo D. T. Torres,
• Gislaine P. Andrade,
• Roseli H. Sato,
• Cibele N. Pedron,
• Tania M. Manieri,
• Giselle Cerchiaro,
• Anderson O. Ribeiro,
• Cesar de la Fuente-Nunez and
• Vani X. Oliveira Jr.

Beilstein J. Org. Chem. 2018, 14, 1693–1703, doi:10.3762/bjoc.14.144

• investigated Dec-NH2, its LZ template and single/double substituted derivatives for their ability to selectively kill MCF-7 breast cancer cells. Results and Discussion Peptide design, chemical synthesis, purification and physicochemical analyses Dec-NH2 is a cationic α-helical antimicrobial and antiparasitic

• cationic peptides. This strategy is based on the electrostatic interaction of the peptides, through their cationic residues, with the anionic phospholipids present in the membrane [39][40]. The peptides accumulate in the membrane, leading to perturbation of membrane integrity and subsequent cell death [40

• ones to the cationic charged residues, the purple circles to the polar uncharged residues and the green circle to a proline residue. The black line denotes hydrophilic and hydrophobic faces of the amphipathic structures. Red arrows show the mutation positions. MTT assays using Dec-NH2 and its synthetic

Glycosylation reactions mediated by hypervalent iodine: application to the synthesis of nucleosides and carbohydrates

• Yuichi Yoshimura,
• Hideaki Wakamatsu,
• Yoshihiro Natori,
• Yukako Saito and
• Noriaki Minakawa

Beilstein J. Org. Chem. 2018, 14, 1595–1618, doi:10.3762/bjoc.14.137

• the hypervalent iodine-mediated glycosylation, a thiosugar donor 83 was oxidized to a cationic intermediate 84 with the assistance of a Lewis acid (TMSOTf) and a base and the subsequent nucleophilic attack of silylated base to 84 gave the desired nucleoside 85. The success of the hypervalent iodine

• react with oxidative agents, it was expected to form a cationic intermediate as in the case of allylsilanes described above. A direct coupling of glycals with nucleobases is challenging, since it is formally a C–N bond-forming reaction with cleaving of the inactive C–H bond at the γ-position. Actually

Cobalt-catalyzed C–H cyanations: Insights into the reaction mechanism and the role of London dispersion

• Eric Detmar,
• Valentin Müller,
• Daniel Zell,
• Lutz Ackermann and
• Martin Breugst

Beilstein J. Org. Chem. 2018, 14, 1537–1545, doi:10.3762/bjoc.14.130

• dissociates and leaves the reaction mixture as a gas. Although the SbF6– counter ion to the cationic cobalt complexes is considered to be weakly coordinating [37], specific interactions cannot be completely ruled out. We have assumed that all of the positively charged cobalt complexes on the reaction path are

Hypervalent organoiodine compounds: from reagents to valuable building blocks in synthesis

• Gwendal Grelier,
• Benjamin Darses and
• Philippe Dauban

Beilstein J. Org. Chem. 2018, 14, 1508–1528, doi:10.3762/bjoc.14.128

• the conversion of allenes 20. A regioselective 1,2-addition on the internal π-bond was observed to afford the products 21, because of the presence of a heteroatom substituent that can stabilize the radical or cationic intermediate by coordination with the copper complex (Scheme 9) [42]. However, the

• supported by DFT calculation have led to propose that the rate-determining step of the process would be the ligand exchange between TFA and the O-enolate (Scheme 41) [79]. The resulting cationic intermediate 88 could rapidly evolve through a [3,3] rearrangement. Even though the C-enolate 89 is more stable

Hyper-reticulated calixarene polymers: a new example of entirely synthetic nanosponge materials

• Alberto Spinella,
• Marco Russo,
• Antonella Di Vincenzo,
• Delia Chillura Martino and
• Paolo Lo Meo

Beilstein J. Org. Chem. 2018, 14, 1498–1507, doi:10.3762/bjoc.14.127

• reported in literature (3.18 ± 0.01), 2 is still in its anionic dissociated form at pH 4.4. Similarly, a neat increase of the sequestration percentage occurs, on increasing the pH from 6.7 to 10.7, for the basic diamine derivative 5 (pKBH+ = 10.19 ± 0.01), which passes from its cationic to its neutral form

• . Consistently with the behavior of ionisable guests 2 and 5, data indicate a significant dependence of the absorption on pH, which can be partly rationalized in terms of charge interactions. Indeed, absorption of cationic toluidine blue 6 regularly increases on increasing the pH, i.e., on decreasing the

Design and biological characterization of novel cell-penetrating peptides preferentially targeting cell nuclei and subnuclear regions

• Anja Gronewold,
• Mareike Horn and
• Ines Neundorf

Beilstein J. Org. Chem. 2018, 14, 1378–1388, doi:10.3762/bjoc.14.116

• C-terminal aa of the cationic antimicrobial peptide CAP18 [18]. When it comes in contact with lipid membranes, it forms a helical structure, probably supporting membrane interaction [19]. However, the main uptake mechanism that was observed followed endocytotic processes, although we have seen that

• residues within the sequences. These effects were already described by other groups working with highly cationic CPPs [29][30][31][32]. Moreover, the formation of amphipathic α-helices is often one major factor for efficient peptide/lipid interaction, initiating the following internalization process [33

Oligonucleotide analogues with cationic backbone linkages

• Melissa Meng and
• Christian Ducho

Beilstein J. Org. Chem. 2018, 14, 1293–1308, doi:10.3762/bjoc.14.111

• aspired improvement of cellular uptake, fully cationic oligonucleotide analogues might also be attractive candidate structures, as indicated by the advantageous properties of cationic cell-penetrating peptides (CPPs) [38]. However, the design of modifications of type 1–6 precludes the preparation of fully

• cationic oligonucleotide analogues. This review focusses on the second aforementioned option to employ cationic motifs in oligonucleotide structures, i.e., as replacements of the native phosphate diester linkages [39]. In principle, this approach enables the preparation of partially or fully zwitterionic

• as well as cationic backbones. This strategy has been studied less frequently, with research on four artificial cationic linkages summarized in this review: aminoalkylated phosphoramidates (and related systems), guanidinium groups, S-methylthiourea motifs, and nucleosyl amino acid (NAA)-derived

Atom-economical group-transfer reactions with hypervalent iodine compounds

• Andreas Boelke,
• Peter Finkbeiner and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2018, 14, 1263–1280, doi:10.3762/bjoc.14.108

• arylation protocols [18][19][20][21][22]. While in solid state they clearly have a T-shaped pseudotrigonal bipyramid structure, the common structural motif for λ3-iodanes, recent theoretical investigations revealed a potential role of the cationic, normal valent tetrahedral form, in atom transfer processes

• and 2-iodomesitylene (2a). Intramolecular cyclization leads to the iminofuranylium intermediate B which affords the cationic isoindolin-1-one structure C via subsequent intramolecular aza-Michael type rearrangement. This intermediate reacts in the final step with the electron-rich 2-iodomesitylene (2a