Total synthesis and biological evaluation of fluorinated cryptophycins

• Christine Weiß,
• Tobias Bogner,
• Benedikt Sammet and
• Norbert Sewald

Beilstein J. Org. Chem. 2012, 8, 2060–2066, doi:10.3762/bjoc.8.231

• [10][11]. Fluorinated drugs are gaining increasing importance, and currently about 20% of all pharmaceuticals on the world market contain fluorine substituents [12][13]. Fluorination is supposed to enhance bioavailability and receptor selectivity. The van der Waals-radius of a fluorine substituent

Influence of intramolecular hydrogen bonds on the binding potential of methylated β-cyclodextrin derivatives

• Gerhard Wenz

Beilstein J. Org. Chem. 2012, 8, 1890–1895, doi:10.3762/bjoc.8.218

• : binding constant; cyclodextrin; hydrogen bond; methylation; regioselective; Introduction Cyclodextrins (CDs) are a well-known class of organic hosts able to include various guests, preferably in aqueous solution [1][2][3]. Inclusion is mainly driven by hydrophobic and van der Waals interactions [4][5][6

Determination of the relative configuration of tropinone and granatanone aldols by using TBDMS ethers

• Ryszard Lazny,
• Aneta Nodzewska,
• Katarzyna Sidorowicz and
• Przemyslaw Kalicki

Beilstein J. Org. Chem. 2012, 8, 1877–1883, doi:10.3762/bjoc.8.216

• exo,anti-5. At this point it was clear that the new aldol isomer must have had the exo,syn configuration. Isomerization of its TBDMS derivative was so facile that its chromatographic purification was hardly possible. This agreed with expectations based on intuitive van der Waals radii and

Self-assembled organic–inorganic magnetic hybrid adsorbent ferrite based on cyclodextrin nanoparticles

• Ângelo M. L. Denadai,
• Frederico B. De Sousa,
• Joel J. Passos,
• Fernando C. Guatimosim,
• Kirla D. Barbosa,
• Ana E. Burgos,
• Fernando Castro de Oliveira,
• Jeann C. da Silva,
• Bernardo R. A. Neves,
• Nelcy D. S. Mohallem and
• Rubén D. Sinisterra

Beilstein J. Org. Chem. 2012, 8, 1867–1876, doi:10.3762/bjoc.8.215

• , suggesting that βCD is able to minimize the ferrite coalescence process in aqueous solution. The ferrite aggregation process may occur in low zeta potential values (−10 mV, see zeta potential data) and is insufficient to avoid van der Waals attraction [30]; however, at pH 7 this self-assembly behavior can

Molecular solubilization of fullerene C₆₀ in water by γ-cyclodextrin thioethers

• Hai Ming Wang and
• Gerhard Wenz

Beilstein J. Org. Chem. 2012, 8, 1644–1651, doi:10.3762/bjoc.8.188

• still greater van der Waals diameter of 1.0 nm [2]. Molecular dynamics studies strongly favour a sandwich-like structure of the complex, in which two γ-CD molecules tightly interact through hydrogen bonds between their secondary rims and in which C60 is situated in the middle at the widest sites of both

Influence of cyclodextrin on the solubility of a classically prepared 2-vinylcyclopropane macromonomer in aqueous solution

• Helmut Ritter,
• Jia Cheng and
• Monir Tabatabai

Beilstein J. Org. Chem. 2012, 8, 1528–1535, doi:10.3762/bjoc.8.173

• different types of molecules with fitting size through van-der-Waals interactions. By formation of such host–guest complex properties, the dissolution behavior of the guest molecules can be changed. Based on this fact numerous applications of β-CDs are reported [17][18][19][20][21][22][23][24][25

The crystal structure of the Dess–Martin periodinane

• Albert Schröckeneder,
• Desiree Stichnoth,
• Peter Mayer and
• Dirk Trauner

Beilstein J. Org. Chem. 2012, 8, 1523–1527, doi:10.3762/bjoc.8.172

• . The intermolecular iodine–oxygen distance of 3.3 Å lies well below the sum of the van der Waals radii (3.46 Å) [11]. Angles of 159.1° (C3a–I1a–O8b) and 120.2° (I1a-O8b-C12b) are also in accordance with the presence of halogen bonds [12]. Similar bonds between iodine atoms and sp2-hybridized oxygen

Synthesis and evaluation of new guanidine-thiourea organocatalyst for the nitro-Michael reaction: Theoretical studies on mechanism and enantioselectivity

• Tatyana E. Shubina,
• Matthias Freund,
• Sebastian Schenker,
• Timothy Clark and
• Svetlana B. Tsogoeva

Beilstein J. Org. Chem. 2012, 8, 1485–1498, doi:10.3762/bjoc.8.168

• (Figure 1), gas-phase DFT, MP2 and DFT-D with van der Waals correction predict 7a to be more stable than 7b by between 1.8 and 7.4 kcal·mol−1 (Figure 1). The MP2 and DFT-D energies agree very well. The two other conformers, 7c and 7d, are less stable than 7a/7b at all levels employed and were therefore

• as DFT-PCM). Single-point MP2 [66] energies with DZ and TZ basis sets were computed at the B3PW91 optimized geometries (denoted as MP2/6–31G(d)//B3PW91/6–31G(d) and MP2/6–311+G(d,p)//B3PW91/6–31G(d), respectively). Single-point DFT calculations with empirical van der Waals corrections [63] were

The preferred conformation of erythro- and threo-1,2-difluorocyclododecanes

• Yi Wang,
• Peer Kirsch,
• Tomas Lebl,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2012, 8, 1271–1278, doi:10.3762/bjoc.8.143

• pointing into the ring on the top face, and four more endo hydrogens pointing into the ring on the lower face. Each set of hydrogens forms a square, and they are spaced at van der Waals contact distances (~2.1–2.2 Å) to their contacted neighbours, situated at 1,4-positions on adjacent edges of the ring

• ][2]. There are four endo hydrogens above and four below the plane of the ring, which are tensioned as they are within van der Waals contact distances. Thus the ring adopts a [3333] square-type structure. (Reproduced with permission from [1]; Copyright © 1960 Verlag GmbH & Co KGaA, Weinheim). Crystal

Investigation of the network of preferred interactions in an artificial coiled-coil association using the peptide array technique

• Raheleh Rezaei Araghi,
• Carsten C. Mahrenholz,
• Rudolf Volkmer and
• Beate Koksch

Beilstein J. Org. Chem. 2012, 8, 640–649, doi:10.3762/bjoc.8.71

• a sufficient number of van der Waals interactions to enable the chimeric sequence to form helical interfaces interacting with a native peptidic partner [20]. These instructive investigations have revealed that side-chain and backbone characteristics are tuneable elements for control of the

Synthesis of fluorinated maltose derivatives for monitoring protein interaction by ¹⁹F NMR

• Michaela Braitsch,
• Hanspeter Kählig,
• Georg Kontaxis,
• Michael Fischer,
• Toshinari Kawada,
• Robert Konrat and
• Walther Schmid

Beilstein J. Org. Chem. 2012, 8, 448–455, doi:10.3762/bjoc.8.51

• maltose and MBP is 12, excluding those with water and between glucose units. The reducing glucose unit (g1) makes about twice as many direct hydrogen bonds with MBP as the nonreducing glucose unit (g2) does (Figure 1). But there is some evidence for the importance of hydrogen bonds and van der Waals

Double N-arylation reaction of polyhalogenated 4,4’-bipyridines. Expedious synthesis of functionalized 2,7-diazacarbazoles

• Mohamed Abboud,
• Emmanuel Aubert and
• Victor Mamane

Beilstein J. Org. Chem. 2012, 8, 253–258, doi:10.3762/bjoc.8.26

• ., van der Waals radii taken into account), large enough to accommodate n-hexane and chloroform molecules, which are disordered. Conclusion In summary, we have described an efficient approach for the synthesis of uncommon 2,7-diazacarbazoles from readily available tetrahalogenated 4,4’-bipyridines. By

Fifty years of oxacalix[3]arenes: A review

• Kevin Cottet,
• Paula M. Marcos and
• Peter J. Cragg

Beilstein J. Org. Chem. 2012, 8, 201–226, doi:10.3762/bjoc.8.22

• the fullerenes is observed. This arrangement maximizes the number of points of contact within the supramolecular complex, thereby enhancing the van der Waals interactions. In the same paper, the association constants of several oxacalix[3]arenes were calculated by the Rose–Drago method based on

The interplay of configuration and conformation in helical perylenequinones: Insights from chirality induction in liquid crystals and calculations

• Elisa Frezza,
• Silvia Pieraccini,
• Stefania Mazzini,
• Alberta Ferrarini and
• Gian Piero Spada

Beilstein J. Org. Chem. 2012, 8, 155–163, doi:10.3762/bjoc.8.16

• following set of van der Waals radii: rH = 0.1 nm, rO = 0.15 nm and rC = 0.185 nm [42], along with a rolling sphere radius equal to 0.3 nm [40] and a density of vertices equal to 500 nm−2. The chirality parameter of a given compound Q, was calculated as where the sum is over all the conformers and gj, wj

Computational evidence for intramolecular hydrogen bonding and nonbonding X···O interactions in 2'-haloflavonols

• Tânia A. O. Fonseca,
• Matheus P. Freitas,
• Rodrigo A. Cormanich,
• Teodorico C. Ramalho,
• Cláudio F. Tormena and
• Roberto Rittner

Beilstein J. Org. Chem. 2012, 8, 112–117, doi:10.3762/bjoc.8.12

• , except for the (C=)O···H(O) interaction in 2'-fluoroflavonol A, which is slightly covalent and, hence, stronger than the remaining ones. The distances between the atoms involved in long-range interactions depicted in Table 2 are always shorter than the sum of their van der Waals radii (the van der Waals

On the mechanism of action of gated molecular baskets: The synchronicity of the revolving motion of gates and in/out trafficking of guests

• Keith Hermann,
• Stephen Rieth,
• Hashem A. Taha,
• Bao-Yu Wang,
• Christopher M. Hadad and
• Jovica D. Badjić

Beilstein J. Org. Chem. 2012, 8, 90–99, doi:10.3762/bjoc.8.9

• of the guest (ΔG°), and (3) the “slippage” of the guest while exiting the open host (ΔG‡sterics) [8][11][21][35]. The encapsulation kinetics is first-order in guest CH3CCl3 suggesting that this species creates van der Waals strain (friction) during the in/out trafficking, thereby justifying the use

Protonation and deprotonation induced organo/hydrogelation: Bile acid derived gelators containing a basic side chain

• Uday Maitra and
• Arkajyoti Chakrabarty

Beilstein J. Org. Chem. 2011, 7, 304–309, doi:10.3762/bjoc.7.40

• -assembled structures form mainly due to weak non-covalent interactions such as hydrogen-bonding, van der Waals forces, π–π interactions, charge-transfer interactions etc. in organogels, whereas, in aqueous gels, the major driving force for aggregation is hydrophobic interaction [2]. A number of

Synthesis of cationic dibenzosemibullvalene-based phase-transfer catalysts by di-π-methane rearrangements of pyrrolinium-annelated dibenzobarrelene derivatives

• Heiko Ihmels and
• Jia Luo

Beilstein J. Org. Chem. 2011, 7, 119–126, doi:10.3762/bjoc.7.17

• amphiphilic tetraalkylammonium derivative that exhibits three different benzene-containing concave sites to which an organic substrate may associate by attractive van der Waals interactions or π-stacking. Moreover, additional functionalities, e.g., hydroxy or amino groups, may be attached to the benzene rings

Expanding the gelation properties of valine-based 3,5-diaminobenzoate organogelators with N-alkylurea functionalities

• Hak-Fun Chow and
• Chin-Ho Cheng

Beilstein J. Org. Chem. 2010, 6, 1015–1021, doi:10.3762/bjoc.6.114

• , precipitation or crystallization will take place. On the other hand, if the interactions are too weak, dissolution of the organogelator will result. In addition, non-specific interactions such as hydrophobic and van der Waals interactions are difficult to quantify, yet they can play very important roles on a

Differences between β-Ala and Gly-Gly in the design of amino acids-based hydrogels

• Andreea Pasc,
• Firmin Obounou Akong,
• Sedat Cosgun and
• Christine Gérardin

Beilstein J. Org. Chem. 2010, 6, 973–977, doi:10.3762/bjoc.6.109

• as electrostatic, hydrogen bonding, dipole–dipole, π–π stacking and hydrophobic/van der Waals interactions. Since the cross-links between fibres are non-covalent in nature, LMWHs exhibit thermoreversibility, rapid response to external stimuli (i.e., stirring, sonication). Among these LMWHs, amino

• solvents, and a hydrophobic domain for van der Waals or hydrophobic interactions (Figure 1). They are able to entrap a large number of solvent molecules per one gelator molecule. Herein the gelators were designed as AA-His-EO2-Alk, bearing i) an hydrophobic alkyl group, ii) a polar peptide group with

Towards racemizable chiral organogelators

• Jian Bin Lin,
• Debarshi Dasgupta,
• Seda Cantekin and
• Albertus P. H. J. Schenning

Beilstein J. Org. Chem. 2010, 6, 960–965, doi:10.3762/bjoc.6.107

• that these hydrogen-bonded dimers or tetramers subsequently stack via π-π interaction and via van der Waals interactions into bundled fibers. Racemization The racemization of R-3 was investigated by chiral HPLC. After adding 1 equivalent of DBU to a solution of R-3 in octane at room temperature

Pyridinium based amphiphilic hydrogelators as potential antibacterial agents

• Sayanti Brahmachari,
• Sisir Debnath,
• Sounak Dutta and
• Prasanta Kumar Das

Beilstein J. Org. Chem. 2010, 6, 859–868, doi:10.3762/bjoc.6.101

• hydrophobic interactions is mandatory for any gelation process. Non-covalent interactions such as hydrogen bonding, ionic interactions, π–π stacking or van der Waals forces play a pivotal role in self-assembled gelation [12]. Tuning the structure of gelator molecules leads to a better understanding of the

Chiral gels derived from secondary ammonium salts of (1R,3S)-(+)-camphoric acid

• Tapas Kumar Adalder,
• N. N. Adarsh,
• Ravish Sankolli and
• Parthasarathi Dastidar

Beilstein J. Org. Chem. 2010, 6, 848–858, doi:10.3762/bjoc.6.100

• can be of two kinds – chemical or polymeric and physical or supramolecular. While covalent bonds are responsible for the formation of 3-D networks in chemical gels, various non-covalent interactions such as hydrogen bonding, π-π stacking, hydrophobic, van der Waals forces etc. are required to form gel

Organic gelators and hydrogelators

• Jean-Pierre Desvergne

Beilstein J. Org. Chem. 2010, 6, 846–847, doi:10.3762/bjoc.6.99

• liquid) which behaves as a visco-elastic material (soft matter) due to the immobilization of solvent molecules in a three-dimensional network. This network results from the self-assembly of the gelling agent into fibres via non-covalent interactions such as hydrogen bonding, π–π stacking, van der Waals

Chromo- and fluorophoric water-soluble polymers and silica particles by nucleophilic substitution reaction of poly(vinyl amine)

• Katja Hofmann,
• Ingolf Kahle,
• Frank Simon and
• Stefan Spange

Beilstein J. Org. Chem. 2010, 6, No. 79, doi:10.3762/bjoc.6.79

• 1 resulting from intermolecular interactions with the surroundings of the molecules, and which of these are dipole–dipole and/or hydrogen-bond interactions. To separate the effects of non-specific van der Waals interactions including electrostatic effects (dipolarity/polarizability) from specific