Complexation of molecular clips containing fragments of diphenylglycoluril and benzocrown ethers with paraquat and its derivatives

• Leonid S. Kikot',
• Catherine Yu. Kulygina,
• Alexander Yu. Lyapunov,
• Svetlana V. Shishkina,
• Roman I. Zubatyuk,
• Tatiana Yu. Bogaschenko and
• Tatiana I. Kirichenko

Beilstein J. Org. Chem. 2017, 13, 2056–2067, doi:10.3762/bjoc.13.203

• its analogues 8–10 (Figure 1). Results and Discussion Complexation studies Paraquat (7) and its derivatives are among the most studied electron-acceptor guests that can form stable inclusion complexes with electron-donating molecules. Stabilization of such inclusion complexes is mainly realized due to

• described by the molecular electrostatic potential (MEP, Figure 2); 2) the number of oxygen atoms of the polyether chain involved in complex stabilization due to intermolecular C–H···О bonds. For qualitative estimation of the complexing properties of the obtained molecular clips 1–6, we used the approach

• clips, as well as through hydrogen bonds between the Hα, Hβ, and CH3 protons of paraquat with oxygen atoms of carbonyl groups in glycoluril fragment. The contribution of the polyether chains to the stabilization of the complex with 1:1 composition, in the first approximation, may be considered as the

Are boat transition states likely to occur in Cope rearrangements? A DFT study of the biogenesis of germacranes

• José Enrique Barquera-Lozada and
• Gabriel Cuevas

Beilstein J. Org. Chem. 2017, 13, 1969–1976, doi:10.3762/bjoc.13.192

• direction there are some examples [37][69][76]. The hemiacetalization by itself does not guarantee the stabilization of an elemane. If compound 1 had to suffer a normal Cope (chair TS), it would generate the C5 epimer of 2 (2’, Figure 2). This epimer is 2.6 kcal/mol less stable than 1a, so the formation of

High-speed vibration-milling-promoted synthesis of symmetrical frameworks containing two or three pyrrole units

• Marco Leonardi,
• Mercedes Villacampa and
• J. Carlos Menéndez

Beilstein J. Org. Chem. 2017, 13, 1957–1962, doi:10.3762/bjoc.13.190

• ) may be hampered by steric hindrance, since this is the only case where R3 is different from H. In the cases of 2-furyl methyl ketone and 2-thienyl methyl ketone, the reason for the lower reactivity under solvent-free conditions may be the stabilization of the intermediate enol via intramolecular

A novel application of 2-silylated 1,3-dithiolanes for the synthesis of aryl/hetaryl-substituted ethenes and dibenzofulvenes

• Grzegorz Mlostoń,
• Paulina Pipiak,
• Róża Hamera-Fałdyga and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 1900–1906, doi:10.3762/bjoc.13.185

• observed. These experiments demonstrate that the 4,5-unsubstituted 1,3-dithiolane carbanions generated under mild conditions through desilylation of the appropriate precursors 13 do not require an electron-withdrawing substituent for their stabilization [29]. The preparation of 1,3-dithianes and 1,3

Conformational impact of structural modifications in 2-fluorocyclohexanone

• Francisco A. Martins,
• Josué M. Silla and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2017, 13, 1781–1787, doi:10.3762/bjoc.13.172

• hydrogen bonding, when possible, is a better source of stabilization, but the interaction of F with Y (or the C=Y bond) appears to be more relevant as the controlling effect of the conformational isomerism of the studied compounds. Thus, classical effects explain satisfactorily the conformational behavior

New electroactive asymmetrical chalcones and therefrom derived 2-amino- / 2-(1H-pyrrol-1-yl)pyrimidines, containing an N-[ω-(4-methoxyphenoxy)alkyl]carbazole fragment: synthesis, optical and electrochemical properties

• Daria G. Selivanova,
• Alexei A. Gorbunov,
• Olga A. Mayorova,
• Alexander N. Vasyanin,
• Igor V. Lunegov,
• Elena V. Shklyaeva and
• Georgii G. Abashev

Beilstein J. Org. Chem. 2017, 13, 1583–1595, doi:10.3762/bjoc.13.158

• absorption maxima and of fluorescence maxima as well, and in the last case this shift is more pronounced. This indicates that the excited state of the molecule is more polar than the ground state, and, therefore, when a solvent is replaced by a more polar one, a large stabilization of the excited state in

Chemical systems, chemical contiguity and the emergence of life

• Terrence P. Kee and
• Pierre-Alain Monnard

Beilstein J. Org. Chem. 2017, 13, 1551–1563, doi:10.3762/bjoc.13.155

• -surfactants, if available via prebiotic syntheses [20][60][61][62], could have also contributed to the formation of primitive amphiphile-based structures, by allowing structure stabilization under prebiotic conditions, e.g., high ionic strength or temperature or stringent pH values. Selective association of

Base-promoted isomerization of CF₃-containing allylic alcohols to the corresponding saturated ketones under metal-free conditions

• Yoko Hamada,
• Tomoko Kawasaki-Takasuka and
• Takashi Yamazaki

Beilstein J. Org. Chem. 2017, 13, 1507–1512, doi:10.3762/bjoc.13.149

• corresponding OH groups. The strongly electron-withdrawing property of a CF3 group is considered to play a key role in stabilization of both 3F-C and 4F-C, and the phenyl group as well as the carbon–carbon multiple bonds would also provide the additional preferable effect by their efficient resonance. In the

2-Methyl-2,4-pentanediol (MPD) boosts as detergent-substitute the performance of ß-barrel hybrid catalyst for phenylacetylene polymerization

• Julia Kinzel,
• Daniel F. Sauer,
• Marco Bocola,
• Marcus Arlt,
• Tayebeh Mirzaei Garakani,
• Andreas Thiel,
• Klaus Beckerle,
• Tino Polen,
• Jun Okuda and
• Ulrich Schwaneberg

Beilstein J. Org. Chem. 2017, 13, 1498–1506, doi:10.3762/bjoc.13.148

• stabilization agents to solubilize purified transmembrane proteins is crucial for their application in aqueous media. The small molecule 2-methyl-2,4-pentanediol (MPD) was used to stabilize the transmembrane protein Ferric hydroxamate uptake protein component A (FhuA) utilized as host for the construction of a

• -160), the formed pore (2.5–3.0 nm) is sufficiently large to harbor sterically demanding catalysts and substrates [28][29]. As a transmembrane protein, FhuA needs stabilization of its hydrophobic transmembrane region in an aqueous environment, which is naturally covered by phospholipids in the outer

• molecules as stabilizing cosolvent to investigate the molecular dynamics of protein structure stabilization, how a small amphiphilic molecule could stabilize a transmembrane protein such as FhuA ΔCVFtev. All simulations started with a random distribution of MPD, but after a few nanoseconds, the MPD

Syntheses of 3,4- and 1,4-dihydroquinazolines from 2-aminobenzylamine

• Jimena E. Díaz,
• Silvia Ranieri,
• Nadia Gruber and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2017, 13, 1470–1477, doi:10.3762/bjoc.13.145

• resonance stabilization of the resulting 2-arylquinazolin-4(1H)-ones 6i,j (Scheme 3). The fact that the yield of the o-methylphenyl-substituted derivative 2j, in which this stabilization is reduced due to steric effects, was higher than for the phenyl-substituted derivative reinforces this hypothesis

1-Imidoalkylphosphonium salts with modulated C_α–P⁺ bond strength: synthesis and application as new active α-imidoalkylating agents

• Jakub Adamek,
• Roman Mazurkiewicz,
• Anna Węgrzyk and
• Karol Erfurt

Beilstein J. Org. Chem. 2017, 13, 1446–1455, doi:10.3762/bjoc.13.142

• was isolated in 73% yield accompanied by only trace amounts of the expected phosphonium salt 5o (Table 2, last entry). It is assumed that both the extraordinary effective resonance stabilization of the imide anion and the excessive steric congestion in the transition state make the splitting of the Cα

An improved preparation of phorbol from croton oil

• Alberto Pagani,
• Simone Gaeta,
• Andrei I. Savchenko,
• Craig M. Williams and
• Giovanni Appendino

Beilstein J. Org. Chem. 2017, 13, 1361–1367, doi:10.3762/bjoc.13.133

• , alternatively, deprotected with acidic methanol (pH 3) to phorbol. The reasons for this trityl-induced stabilization are unclear, an educated guess being that the bulky trityl group could hinder oxidative reactions based on oxygen attack to the ring B double bond, a major degradation pathway for phorbol

Aggregation behaviour of a single-chain, phenylene-modified bolalipid and its miscibility with classical phospholipids

• Simon Drescher,
• Vasil M. Garamus,
• Christopher J. Garvey,
• Annette Meister and
• Alfred Blume

Beilstein J. Org. Chem. 2017, 13, 995–1007, doi:10.3762/bjoc.13.99

• unmodified bolalipids, such as PC-C32-PC, could not be incorporated into bilayers of DMPC or POPC [28]. In contrast, bolalipids with an alkyl chain modification, e.g., PC-C17pPhC17-PC, were partially miscible with DPPC and DSPC. But, closed lipid vesicles (liposomes) and a pronounced stabilization of the

Conformational study of L-methionine and L-cysteine derivatives through quantum chemical calculations and ³J_HH coupling constant analyses

• Weslley G. D. P. Silva,
• Carolyne B. Braga and
• Roberto Rittner

Beilstein J. Org. Chem. 2017, 13, 925–937, doi:10.3762/bjoc.13.94

• difference between 3JHaHb1,obs and 3JHaHb2,obs increases to almost 4.0 Hz in DMSO and this fact is related to the stabilization of conformers c, which have Ha anti to Hb1, and gauche to Hb2 (Table 5). Unlike 3, the 3JHaHb1,obs and 3JHaHb2,obs for compound 4 exhibit close values in CHCl3 (3.9 and 4.3 Hz

• , respectively), and this also suggests the predominance of conformers a in this less polar solvent. However, despite conformers a of 4 being more populated in all studied media, 3JHaHb2,obs increases from 4.3 Hz in CDCl3 to 7.5 Hz in DMSO, and it indicates the stabilization of conformers b in more polar

DMAP-assisted sulfonylation as an efficient step for the methylation of primary amine motifs on solid support

• Johnny N. Naoum,
• Koushik Chandra,
• Dorit Shemesh,
• R. Benny Gerber,
• Chaim Gilon and
• Mattan Hurevich

Beilstein J. Org. Chem. 2017, 13, 806–816, doi:10.3762/bjoc.13.81

• that these transformations proceed via a stable sulfonyl-DMAP intermediate [31][32][33][34]. Although many reported mechanistic studies reflect on the unique significance of the para-dialkylamino group [32] to the stabilization of the intermediate, DMAP was never reported to be used as the sole

• forming a stable reactive intermediate that lowers the overall energy barrier. This stabilization effect is unique to para-dialkylaminopyridine derivatives and much less significant for other pyridine type analogues like collidine. We suggested that the significant effect of DMAP compared to that of

• ion that contributes to the stabilization of the positive charge of the intermediate [41][42][43][44]. Figure 4a compares the energy of the o-NBS and the collidine reactants to the energy of the corresponding intermediate. As can be seen, the energy difference between both structures is quite large

Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes

• Carmen Moreno-Marrodan,
• Francesca Liguori and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2017, 13, 734–754, doi:10.3762/bjoc.13.73

• ). The preferred choice are mesoporous supports (2–50 nm cavity size), due to the enhanced contact with the reagents because of the high surface area [89][90] and the effective “steric” stabilization of the embedded metal nanoparticle catalysts [91][92]. However, mesoporous catalysts may suffer from pore

• clogging, active sites accessibility, mass transfer limitations, and lack of reproducibility. Additional stabilization of MNP can be also achieved either by: the “electrostatic” effect of charged functional groups grafted to the support, a common strategy in gel-type resins (e.g., sulfonic resins) [93

• ]; the strong metal–support interactions, particularly for inorganic oxide materials, e.g., TiO2 [94][95]. Besides contributing to catalyst resistance by hampering the loss and the size increase of active sites, MNP stabilization is a key factor to limit the amount of metal leached in solution, an issue

Substitution of fluorine in M[C₆F₅BF₃] with organolithium compounds: distinctions between O- and N-nucleophiles

• Anton Yu. Shabalin,
• Nicolay Yu. Adonin and
• Vadim V. Bardin

Beilstein J. Org. Chem. 2017, 13, 703–713, doi:10.3762/bjoc.13.69

• ) (Table 3, entries 2, 3 and 6). Other data from Table 3 are not reliable for comparison because the initial ratio is remarkably corrupted by the further reactions. We believe that the enrichment of the reaction mixture in [2-PhC6F4BF3]− occurs because of an additional stabilization of transition state A

Dimerization reactions of aryl selenophen-2-yl-substituted thiocarbonyl S-methanides as diradical processes: a computational study

• Michael L. McKee,
• Grzegorz Mlostoń,
• Katarzyna Urbaniak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 410–416, doi:10.3762/bjoc.13.44

• intermediate, delocalized diradical species. The influence of selenium as a ‘heavy atom’ for stabilization of this intermediate has been emphasized. Keywords: 1,3-dipolar cycloadditions; reaction mechanisms; reactive intermediates; thiocarbonyl S-methanides; thioketones; Introduction Thiocarbonyl S

Adsorption of RNA on mineral surfaces and mineral precipitates

• Elisa Biondi,
• Yoshihiro Furukawa,
• Jun Kawai and
• Steven A. Benner

Beilstein J. Org. Chem. 2017, 13, 393–404, doi:10.3762/bjoc.13.42

• sulfate minerals, where those trends are the same when measured in natural and synthetic minerals. They are also validated by comparison of co-precipitated synthetic minerals. We also show differential binding of RNA to polymorphic forms of calcium carbonate, and the stabilization of bound RNA on

• aragonite. These have relevance to the prebiotic stabilization of RNA, where such carbonate minerals are expected to have been abundant, as they appear to be today on Mars. Keywords: carbonates; natural minerals; origins of life; RNA adsorption; synthetic minerals; Introduction It has been nearly 70 years

• RNA. Silicates, of course, are represented by a very large number of minerals, and this work examined only a very small fraction of these. We recently reported work examining the adsorption and stabilization of RNA on opal [23]. Polymorphism Another layer of complexity comes from the fact that the

Polyketide stereocontrol: a study in chemical biology

• Kira J. Weissman

Beilstein J. Org. Chem. 2017, 13, 348–371, doi:10.3762/bjoc.13.39

• ][84][85], the origin of this stabilization remains unknown. KRs were first suggested to act as epimerases – despite the fact that no other SDR enzyme exhibits this activity – based on structural analysis [57]. This proposal led to the classification of PKS KRs working on C-2 methylated substrates into

NMR reaction monitoring in flow synthesis

• M. Victoria Gomez and
• Antonio de la Hoz

Beilstein J. Org. Chem. 2017, 13, 285–300, doi:10.3762/bjoc.13.31

• microreactor before temperature stabilization, each with a different temperature value. Finally, zone d includes the data points that experienced the constant temperature of 393 K for 4 minutes (but with a difference in ‘starting’ concentration from that of zone b'). Fitting these data, i.e., temperature

Highly bulky and stable geometry-constrained iminopyridines: Synthesis, structure and application in Pd-catalyzed Suzuki coupling of aryl chlorides

• Yi Lai,
• Zhijian Zong,
• Yujie Tang,
• Weimin Mo,
• Nan Sun,
• Baoxiang Hu,
• Zhenlu Shen,
• Liqun Jin,
• Wen-hua Sun and
• Xinquan Hu

Beilstein J. Org. Chem. 2017, 13, 213–221, doi:10.3762/bjoc.13.24

• activities the importance of bulkier groups at the imino moiety for the stabilization of the palladium species was sown. A variety of aryl chlorides and arylboronic acids were successfully coupled in high yields and selectivity. Experimental General procedures All reactions were carried out under air

Interactions between photoacidic 3-hydroxynaphtho[1,2-b]quinolizinium and cucurbit[7]uril: Influence on acidity in the ground and excited state

• Jonas Becher,
• Daria V. Berdnikova,
• Darinka Dzubiel,
• Heiko Ihmels and
• Phil M. Pithan

Beilstein J. Org. Chem. 2017, 13, 203–212, doi:10.3762/bjoc.13.23

• the binding constants of complexes between cationic ligands and cucurbiturils depend not only on the actual fit of the ligand to the host structure. In this particular case, the stabilization/destabilization of the free ligand in water, and for that matter the hydrophobic effect, may influence the

• increase of the pKa and pKa* values originates from the interaction of the acidic functionality with the carbonyl groups at the outer rim of the host molecule [34][55] and – as shown for cationic ligands – from the stabilization of the positive charge by the accommodation in the binding site [29

A postsynthetically 2’-“clickable” uridine with arabino configuration and its application for fluorescent labeling and imaging of DNA

• Heidi-Kristin Walter,
• Bettina Olshausen,
• Ute Schepers and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2017, 13, 127–137, doi:10.3762/bjoc.13.16

• , respectively. This small difference tracks well with the general observation that arabino-configured nucleic acids in general show lower stabilities than the ribo-configured ones. With the attached dyes, the arabino-modified duplexes show a smaller stabilization effect by the dyes than the corresponding ribo

• -modified duplexes. The stabilization of dsDNA2a ranges only from 0.7 °C for D1 to 3.2 °C for D3 and D4, whereas the stabilizing effects for dsDNA2r are more diverse, ranging from 2.0 °C for D1 to 3.7 °C for D3. Obviously, the dye interactions with double-stranded DNA do slightly depend on the type of dye

Supramolecular frameworks based on [60]fullerene hexakisadducts

• Andreas Kraft,
• Johannes Stangl,
• Ana-Maria Krause,
• Klaus Müller-Buschbaum and
• Florian Beuerle

Beilstein J. Org. Chem. 2017, 13, 1–9, doi:10.3762/bjoc.13.1

• activation might be that the flexible nature of the alkyl spacers facilitates structural reorganization resulting in a potential blocking of the channels after removal of the solvent molecules. The Et2O molecules appear to play a crucial role for the stabilization of both channel size and shape. For future