Hydroquinone–pyrrole dyads with varied linkers

• Hao Huang,
• Christoffer Karlsson,
• Maria Strømme,
• Martin Sjödin and
• Adolf Gogoll

Beilstein J. Org. Chem. 2016, 12, 89–96, doi:10.3762/bjoc.12.10

• , Box 576, SE-751 23 Uppsala, Sweden 10.3762/bjoc.12.10 Abstract A series of pyrroles functionalized in the 3-position with p-dimethoxybenzene via various linkers (CH2, CH2CH2, CH=CH, C≡C) has been synthesized. Their electronic properties have been deduced from 1H NMR, 13C NMR, and UV–vis spectra to

• detect possible interactions between the two aromatic subunits. The extent of conjugation between the subunits is largely controlled by the nature of the linker, with the largest conjugation found with the trans-ethene linker and the weakest with the aliphatic linkers. DFT calculations revealed

• different linkers between the pyrrole and hydroquinone subunits was designed [6]. Although it is known that N-protected pyrrole (Py) can be selectively functionalized at the β-position [7], we found the published procedures to be unsuitable for our purpose (vide infra). Therefore, we have developed improved

Supramolecular polymer assembly in aqueous solution arising from cyclodextrin host–guest complexation

• Jie Wang,
• Zhiqiang Qiu,
• Yiming Wang,
• Li Li,
• Xuhong Guo,
• Duc-Truc Pham,
• Stephen F. Lincoln and
• Robert K. Prud’homme

Beilstein J. Org. Chem. 2016, 12, 50–72, doi:10.3762/bjoc.12.7

• [76]. (The 66 prefix in 66β-CD2su and 66β-CD2ur indicates that the succinamide and urea linkers are attached to the C6 carbon in a D-glucopyranose subunit of each β-CD.) The increasing length of the adamantyl tether from amido to hexylamido in PAAAD and PAAADhn progressively decreases steric hindrance

• M−1 in aqueous solution at 298.2 K for β-CD and the β-CD dimer b and the β-CD dimer c, respectively, where the greater β-CD dimer c complex stability was attributed to the greater hydrophobicity arising from the two octamethylene linkers. Rheological studies of aqueous solutions of adamantyl

• . A much greater increase in viscosity was observed when the β-CD dimer c was employed consistent with its greater rigidity derived from the twin octamethylene linkers enhancing interchain cross-link formation. Interesting variations on the above complexation studies are those relating to β-CD

Effective immobilisation of a metathesis catalyst bearing an ammonium-tagged NHC ligand on various solid supports

• Krzysztof Skowerski,
• Jacek Białecki,
• Stefan J. Czarnocki,
• Karolina Żukowska and
• Karol Grela

Beilstein J. Org. Chem. 2016, 12, 5–15, doi:10.3762/bjoc.12.2

• the need for sophisticated linkers and tags, is significantly more complicated. Several protocols were developed for heterogenisation of ruthenium catalysts and this topic has been thoroughly reviewed [8][9][10][11][12][13][14][15][16][17][18]. The implementation of such concepts requires the presence

Polydisperse methyl β-cyclodextrin–epichlorohydrin polymers: variable contact time ¹³C CP-MAS solid-state NMR characterization

• Isabelle Mallard,
• Davy Baudelet,
• Franca Castiglione,
• Monica Ferro,
• Walter Panzeri,
• Enzio Ragg and
• Andrea Mele

Beilstein J. Org. Chem. 2015, 11, 2785–2794, doi:10.3762/bjoc.11.299

• remove organic pollutants [6][11][12][13] and heavy metals [14] from water. The most efficient method for the synthesis of insoluble polymers is to use di- or polyfunctional linkers with monomers of cyclodextrins. Different effective crosslinkers have been reported in the literature such as

Synthesis, structure, and mechanical properties of silica nanocomposite polyrotaxane gels

• Kazuaki Kato,
• Daisuke Matsui,
• Koichi Mayumi and
• Kohzo Ito

Beilstein J. Org. Chem. 2015, 11, 2194–2201, doi:10.3762/bjoc.11.238

• not occur without silica. This suggests that the silica nanoparticles behave as cross-linkers. Viscoelastic measurements of the nanocomposite gels showed no stress relaxation regardless of the silica content for <20% compression strain, indicating an infinite stable network without physical cross

• polymer chains were not directly bonded but rather mechanically interlocked to the silica surfaces. The silica nanoparticles were homogeneously distributed in the gel and worked as cross-linkers to immobilize the cyclic components of the polyrotaxanes on the silica surfaces. As the backbone polymer chains

Ru complexes of Hoveyda–Grubbs type immobilized on lamellar zeolites: activity in olefin metathesis reactions

• Hynek Balcar,
• Naděžda Žilková,
• Martin Kubů,
• Michal Mazur,
• Zdeněk Bastl and
• Jiří Čejka

Beilstein J. Org. Chem. 2015, 11, 2087–2096, doi:10.3762/bjoc.11.225

• developed [1][5][13]; most of them are based on surface modification by specially designed linkers providing covalent bond linkage between the support and Ru complex. Hoveyda–Grubbs type catalysts are also capable of direct (linker-free) immobilization by means of non-covalent interactions [8][14][15][16

A new approach to ferrocene derived alkenes via copper-catalyzed olefination

• Vasily M. Muzalevskiy,
• Aleksei V. Shastin,
• Alexandra D. Demidovich,
• Namiq G. Shikhaliev,
• Abel M. Magerramov,
• Victor N. Khrustalev,
• Rustem D. Rakhimov,
• Sergey Z. Vatsadze and
• Valentine G. Nenajdenko

Beilstein J. Org. Chem. 2015, 11, 2072–2078, doi:10.3762/bjoc.11.223

• ]). Ethynylferrocenes are one of the most popular and extremely effective starting compounds in the creation of ferrocenyl polymers. They are widely used for making both polyferrocenylvinylenes (double bond linkers) [17][18][19][20][21] and polyethynylferrocenes (triple bond linkers) [22][23][24][25]. There are several

Supramolecular chemistry: from aromatic foldamers to solution-phase supramolecular organic frameworks

• Zhan-Ting Li

Beilstein J. Org. Chem. 2015, 11, 2057–2071, doi:10.3762/bjoc.11.222

• . Under low temperature, this dynamic [2]catenane could be quantitatively generated. The intramolecular hydrogen bonds formed by the aromatic amide linkers remarkably enhanced the complexation of the porphyrin units towards the fullerene and the bipyridine ligand. Jiang further introduced amide subunits

• folding of the same series of benzene/triazole oligomers [10]. Recently, Jiang and co-workers reported that when fluorine or chlorine was introduced to the 2-position of the meta-substituted benzene linkers, the corresponding triazole oligomers folded to give new foldamers, which were stabilized by

Dicarboxylic esters: Useful tools for the biocatalyzed synthesis of hybrid compounds and polymers

• Ivan Bassanini,
• Karl Hult and
• Sergio Riva

Beilstein J. Org. Chem. 2015, 11, 1583–1595, doi:10.3762/bjoc.11.174

• polymerization of tubulin in vitro. The same methodology might be applied to direct a drug by conjugation to a molecule binding to a specific receptor on cancer cells. Moreover, by using dicarboxylated linkers with a disulfide bridge, it was possible to generate dynamic libraries of dimeric hybrids based on

Preparative semiconductor photoredox catalysis: An emerging theme in organic synthesis

• David W. Manley and
• John C. Walton

Beilstein J. Org. Chem. 2015, 11, 1570–1582, doi:10.3762/bjoc.11.173

• methylene linker, gave doubly reduced 42a as the major product. Pleasingly, however, the dioxadibenzenacyclododecaphane 41a was also obtained in a modest yield (13%). Diacids 40b and 40c were designed with rigid, planar phenyl ring linkers. TiO2 SCPC of the ortho-analogue 40b was more successful with the

Interactions between tetrathiafulvalene units in dimeric structures – the influence of cyclic cores

• Huixin Jiang,
• Virginia Mazzanti,
• Christian R. Parker,
• Søren Lindbæk Broman,
• Jens Heide Wallberg,
• Karol Lušpai,
• Adam Brincko,
• Henrik G. Kjaergaard,
• Anders Kadziola,
• Peter Rapta,
• Ole Hammerich and
• Mogens Brøndsted Nielsen

Beilstein J. Org. Chem. 2015, 11, 930–948, doi:10.3762/bjoc.11.104

• -ethynylpyridine linkers. When two TTFs are closer together via an ethyne spacer (4), the two waves are rather broad. In fact, a shoulder can be seen for each wave, which indicates weak interactions between the two units, not only for generating two TTF radical cation units, but also for the final generation of

Adsorption mechanism and valency of catechol-functionalized hyperbranched polyglycerols

• Stefanie Krysiak,
• Qiang Wei,
• Klaus Rischka,
• Andreas Hartwig,
• Rainer Haag and
• Thorsten Hugel

Beilstein J. Org. Chem. 2015, 11, 828–836, doi:10.3762/bjoc.11.92

• catechol anchor and the second with two catecholic anchors. Note that in the last case, two catechols with two PEG linkers were involved that shared the applied force. Therefore, the triple maximum force peak with forces of up to 2 nN could be measured despite rupture forces of 1.4 nN for the Si–O bond

• linkers. A) Force–distance curves where the rupture is not smooth but rather interrupted by a cluster of measurement points. This inter-rupture force is indicated by a red arrow. B) Same curve as in A) depicted as force vs time. C) Histograms of inter-rupture forces for the different dwell times

Influence of length and flexibility of spacers on the binding affinity of divalent ligands

• Susanne Liese and
• Roland R. Netz

Beilstein J. Org. Chem. 2015, 11, 804–816, doi:10.3762/bjoc.11.90

• also the maximum and width of the RBA are in this case determined by the binding range σ. In Figure 5b we assume a DNA spacer that is decorated with flexible PEG linkers at both ends. The PEG linkers consist of four monomers each. Assuming Gaussian-chain behavior with a segment length of b = 0.38 nm

• [29], the fluctuations of the PEG linkers and hence the fluctuations of the whole ligand sum up to Δr = 0.5 nm. The shape of the RBA now is much broader, showing that the ligand is less affected by a mismatch between spacer length and distance between the binding pockets. Additionally, we obtain = 5

• attached via two PEG linkers. Linker length and binding range are set to be identical to the example presented in Figure 5b. The average end-to-end distance of the DNA spacer is either chosen to be equal to d (black, continuous line), or is chosen to be too short by 0.7 nm, which mimics the length of two

Probing multivalency in ligand–receptor-mediated adhesion of soft, biomimetic interfaces

• Stephan Schmidt,
• Hanqing Wang,
• Daniel Pussak,
• Simone Mosca and
• Laura Hartmann

Beilstein J. Org. Chem. 2015, 11, 720–729, doi:10.3762/bjoc.11.82

• generally low affinity between sugars and receptors and possibly also by the high flexibility of the polymeric mannose linkers [9]. High molecular flexibility causes a high degree of conformational entropy that negatively affects complex formation between ligands and receptors [23]. Also the design of the

DNA display of glycoconjugates to emulate oligomeric interactions of glycans

• Alexandre Novoa and
• Nicolas Winssinger

Beilstein J. Org. Chem. 2015, 11, 707–719, doi:10.3762/bjoc.11.81

• diverse glycans could be iteratively introduced on amino acid linkers. Inspired by Shoda’s activation [40] which provides facile access to complex glycosyl azides from native carbohydrates, we subsequently applied reiterative CuAAC conjugation of glycans on propargyl glycine residues within a peptide [41

• instructions. To this end a pilot library of fourteen PNA-tagged glycoconjugates that included mannose disaccharides joined by linkers of different lengths were paired through hybridization, varying the ligand combinations and interligand distances. Measuring the affinity of 32 different assemblies against

• between the glycan units and the distinct spatial arrangement conferred by the different linkers. This library represents the largest array of heteroglycan conjugates reported to date. Based on the results obtained with the screen for LecA, a lectin intimately involved in the pathogenicity of P

First principle investigation of the linker length effects on the thermodynamics of divalent pseudorotaxanes

• Andreas J. Achazi,
• Doreen Mollenhauer and
• Beate Paulus

Beilstein J. Org. Chem. 2015, 11, 687–692, doi:10.3762/bjoc.11.78

• energies of association (Gibbs free (binding) energies) for divalent crown-8/ammonium pseudorotaxanes are determined by investigating the influence of different linkers onto the binding. Calculations are performed with density functional theory including dispersion corrections. The translational

• linker shows an enhanced binding strength due to electronic effects, namely the dispersion interaction between the linkers from the guest and the host. For the longer linkers this ideal packing is not possible due to steric hindrance. Keywords: density functional theory (DFT); dispersion correction

• different linkers. The shortest linker shows a much larger chelate cooperativity than the longer linkers due to non-innocent linkers that contribute to the binding. To analyze the individual contributions to the binding, we perform first principle calculations of the model system shown in Figure 1, which is

Design, synthesis and photochemical properties of the first examples of iminosugar clusters based on fluorescent cores

• Mathieu L. Lepage,
• Antoine Mirloup,
• Manon Ripoll,
• Fabien Stauffert,
• Anne Bodlenner,
• Raymond Ziessel and
• Philippe Compain

Beilstein J. Org. Chem. 2015, 11, 659–667, doi:10.3762/bjoc.11.74

• per DNJ unit) [11][12]. In the following years, an impressive ever-growing number of multivalent iminosugars based on various scaffolds, ligands and linkers have been synthesized to further investigate the impact of multivalency on glycosidase inhibition [9][10][11][12][13][14][15][16][17][18][19][20

Synthesis of multivalent carbohydrate mimetics with aminopolyol end groups and their evaluation as L-selectin inhibitors

• Joana Salta,
• Jens Dernedde and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2015, 11, 638–646, doi:10.3762/bjoc.11.72

• able to compare aminopyran 1 with aminopolyol 2 two divalent amides were synthesized from compound 16 using the same carboxylic acid dichlorides 7 and 8 as linkers affording the desired compounds 18 and 19 in excellent yields (Table 2, entries 1 and 2). Moreover, another divalent amide 20 with a longer

Synthesis and surface grafting of a β-cyclodextrin dimer facilitating cooperative inclusion of 2,6-ANS

• Lars W. Städe,
• Thorbjørn T. Nielsen,
• Laurent Duroux,
• Reinhard Wimmer,
• Kyoko Shimizu and
• Kim L. Larsen

Beilstein J. Org. Chem. 2015, 11, 514–523, doi:10.3762/bjoc.11.58

• demonstrated that the choice of linker is an important parameter in order to fully access both cavities [12][13]. Specifically, it was demonstrated that long and/or hydrophobic linkers may induce an inversion process, resulting in self-inclusion of the linker in one of the cavities, thereby limiting

C-5’-Triazolyl-2’-oxa-3’-aza-4’a-carbanucleosides: Synthesis and biological evaluation

• Roberto Romeo,
• Caterina Carnovale,
• Salvatore V. Giofrè,
• Maria A. Chiacchio,
• Adriana Garozzo,
• Emanuele Amata,
• Giovanni Romeo and
• Ugo Chiacchio

Beilstein J. Org. Chem. 2015, 11, 328–334, doi:10.3762/bjoc.11.38

• can interact with intracellular targets to induce cytotoxicity [28][29][30][31][32]. Several functionalities have been inserted as linkers on the 2’-oxa-3’-aza-4’a-carbanucleoside skeleton in order to confer novel mechanisms of action for nucleoside mimics: in this context, the 1,2,3-triazole unit

Come-back of phenanthridine and phenanthridinium derivatives in the 21st century

• Lidija-Marija Tumir,
• Marijana Radić Stojković and
• Ivo Piantanida

Beilstein J. Org. Chem. 2014, 10, 2930–2954, doi:10.3762/bjoc.10.312

• phenanthridine moiety – many ethidium bromide-based dimers were prepared and reviewed in the last two decades of the 20th century, thus here will be presented results from 2000 on. Systematic variation of steric and/or electrostatic effects by means of type, number, length and flexibility of linkers connecting

• intercalator able to differentiate between A–U(T) and G–C base pairs by sign of opposite fluorimetric response. An introduction of the permanent positive charge by methylation of the heterocyclic nitrogen changed the binding mode of the conjugates with shorter linkers from minor groove binding to intercalation

• RNA dyes. Another large series of phenanthridinium-homodimers was constructed by linking two ethidium bromide subunits by peptide-like linkers of variable flexibility and rich in hydrogen-bonding possibilities within the DNA grooves (Figure 5). The resulting bis-intercalators (in comparison to the

Synthesis and characterization of a new photoinduced switchable β-cyclodextrin dimer

• Florian Hamon,
• Claire Blaszkiewicz,
• Marie Buchotte,
• Estelle Banaszak-Léonard,
• Hervé Bricout,
• Sébastien Tilloy,
• Eric Monflier,
• Christine Cézard,
• Laurent Bouteiller,
• Christophe Len and
• Florence Djedaini-Pilard

Beilstein J. Org. Chem. 2014, 10, 2874–2885, doi:10.3762/bjoc.10.304

• to the guest molecules [9][10]. These cyclodextrins linked by ester [11], thioether [12][13][14][15][16], urea [17][18][19], or triazole [20] moieties have been previously described. In addition, aromatic azobenzenes are excellent candidates as molecular switch linkers as they have two forms, namely

• cyclic polymers are aggregated into larger objects stabilized by hydrogen bonds between cyclodextrin moieties and by π-stacking interactions between azobenzene linkers. Finally, according to the computational data, the complexes of AZO-CDim 1 with ADAdim 4 are further stabilized by intramolecular

Synthesis of nanodiamond derivatives carrying amino functions and quantification by a modified Kaiser test

• Gerald Jarre,
• Steffen Heyer,
• Elisabeth Memmel,
• Thomas Meinhardt and
• Anke Krueger

Beilstein J. Org. Chem. 2014, 10, 2729–2737, doi:10.3762/bjoc.10.288

• with amino groups is typically not complete and the stability of amino groups directly bound to the diamond surface is limited as they are at least partially replaced by hydroxy groups under ambient conditions [4]. Therefore, in most cases linkers are used in order to establish stable bonding

• , the linkers are coupled to the diamond surface via heteroatoms. These sites are more easily cleaved compared to carbon–carbon single bonds, e.g., in a physiological environment or other aqueous conditions. It is hence of interest to develop methods that form stable bonds between the diamond surface

• ) BH3·THF, f) Δ, 1,2-dichlorobenzene, g) MCPBA, h) NH3, i) BH3·THF, j) APTMS, k) 4-aminobenzyl(N-Boc)amine, isopentyl nitrite, l) TFA. Surface loading of nanodiamond-carrying amino groups on different linkers using three independent quantification methods. Supporting Information Supporting Information

Synthesis and characterization of a hyper-branched water-soluble β-cyclodextrin polymer

• Francesco Trotta,
• Fabrizio Caldera,
• Roberta Cavalli,
• Andrea Mele,
• Carlo Punta,
• Lucio Melone,
• Franca Castiglione,
• Barbara Rossi,
• Monica Ferro,
• Vincenza Crupi,
• Domenico Majolino,
• Valentina Venuti and
• Dominique Scalarone

Beilstein J. Org. Chem. 2014, 10, 2586–2593, doi:10.3762/bjoc.10.271

• structural aspects and functional properties, and in particular pyromellitic nanosponges were found to present a critical cross-linking value [17]. In other words, the maximum number of cross-linkers per monomer was proved to be around 6 (i.e., 6 mol of pyromellitic dianhydride for each mol of β-CD). If the

Towards the sequence-specific multivalent molecular recognition of cyclodextrin oligomers

• Michael Kurlemann and
• Bart Jan Ravoo

Beilstein J. Org. Chem. 2014, 10, 2428–2440, doi:10.3762/bjoc.10.253

• for the interaction with α-CD, the EM cannot be increased that easy. Here the linkers of the guest and the host moieties have a crucial influence on the structure of the divalent molecules and the host–guest complexes before the intramolecular complexation [1]. Changes in the linkers’ structures can