Diels–Alder reactions in confined spaces: the influence of catalyst structure and the nature of active sites for the retro-Diels–Alder reaction

• Ángel Cantín,
• M. Victoria Gomez and
• Antonio de la Hoz

Beilstein J. Org. Chem. 2016, 12, 2181–2188, doi:10.3762/bjoc.12.208

• and selectivity is the special confinement of the reactants and the presence of catalytic active sites, [15][16] by use of microporous materials doped with metals. While pore dimensions and topology of the microporous materials can affect the selectivity of the reaction, their activity can be strongly

Silica-supported sulfonic acids as recyclable catalyst for esterification of levulinic acid with stoichiometric amounts of alcohols

• Raimondo Maggi,
• N. Raveendran Shiju,
• Veronica Santacroce,
• Giovanni Maestri,
• Franca Bigi and
• Gadi Rothenberg

Beilstein J. Org. Chem. 2016, 12, 2173–2180, doi:10.3762/bjoc.12.207

• catalysts operate under mild conditions and give good conversion and selectivity with stoichiometric amounts of alcohols. The sulfonic acid groups are tethered to the support using organic tethers. These tethers may help in preventing the deactivation of the active sites in the presence of water. Keywords

Chiral ammonium betaine-catalyzed asymmetric Mannich-type reaction of oxindoles

• Masahiro Torii,
• Kohsuke Kato,
• Daisuke Uraguchi and
• Takashi Ooi

Beilstein J. Org. Chem. 2016, 12, 2099–2103, doi:10.3762/bjoc.12.199

• extended steric hindrance over the catalytically active sites, eroded the catalytic activity and diastereocontrol (Table 1, entry 6). These observations demonstrated the superior capability of 1c in facilitating this stereoselective Mannich-type transformation, for which the loading was reduced to 1 mol

Cross-linked cyclodextrin-based material for treatment of metals and organic substances present in industrial discharge waters

• Élise Euvrard,
• Nadia Morin-Crini,
• Coline Druart,
• Justine Bugnet,
• Bernard Martel,
• Cesare Cosentino,
• Virginie Moutarlier and
• Grégorio Crini

Beilstein J. Org. Chem. 2016, 12, 1826–1838, doi:10.3762/bjoc.12.172

• to the active sites [22][23][24][25]. These observations were confirmed by the tests conducted in SS in the presence of calcium. An increase of polymer concentration in DWs (10 g·L−1 instead of 2 g·L−1) yielded better results in terms of removal efficiency for all metals. However, while the retention

Three-component synthesis of highly functionalized aziridines containing a peptide side chain and their one-step transformation into β-functionalized α-ketoamides

• Lena Huck,
• Juan F. González,
• Elena de la Cuesta and
• J. Carlos Menéndez

Beilstein J. Org. Chem. 2016, 12, 1772–1777, doi:10.3762/bjoc.12.166

• hydroxy groups at the active sites of a variety of enzymes. Existing synthetic approaches to this moiety are normally quite complex and do not easily allow the presence of amino acid side chains on the amide nitrogen [23]. Finally, in order to further underscore the synthetic usefulness of these aziridine

Dynamic behavior of rearranging carbocations – implications for terpene biosynthesis

• Stephanie R. Hare and
• Dean J. Tantillo

Beilstein J. Org. Chem. 2016, 12, 377–390, doi:10.3762/bjoc.12.41

• the absence of specifically oriented noncovalent interactions with groups in terpene synthase active sites. Molecular dynamics calculations using the full bornyl diphosphate synthase enzyme were also carried out (here using a combination of DFT and molecular mechanics) [21][22]. These simulations

Organocatalytic asymmetric Henry reaction of 1H-pyrrole-2,3-diones with bifunctional amine-thiourea catalysts bearing multiple hydrogen-bond donors

• Ming-Liang Zhang,
• Deng-Feng Yue,
• Zhen-Hua Wang,
• Yuan Luo,
• Xiao-Ying Xu,
• Xiao-Mei Zhang and
• Wei-Cheng Yuan

Beilstein J. Org. Chem. 2016, 12, 295–300, doi:10.3762/bjoc.12.31

• demonstrated to be an effective and versatile strategy in facilitating a variety of organic transformations over the past decade, and numerous catalytic asymmetric reactions have been developed with various activation modes [1][2][3][4][5][6]. In this realm, chiral bifunctional catalysts, possessing two active

• sites, have captured tremendous attention in particular due to their unique ability of the simultaneous activation of the nucleophile and the electrophile in the same transition state [7][8][9][10][11]. Among them, chiral bifunctional thioureas bearing multiple hydrogen-bond donors have been

Gold(I)-catalysed synthesis of a furan analogue of thiamine pyrophosphate

• Amjid Iqbal,
• El-Habib Sahraoui and
• Finian J. Leeper

Beilstein J. Org. Chem. 2014, 10, 2580–2585, doi:10.3762/bjoc.10.270

• by furan 17 The furan analogue of ThDP, 17, was tested as an inhibitor of pyruvate decarboxylase from Zymomonas mobilis (ZmPDC). ZmPDC is a tetramer, made up of a dimer of dimers, and there are four active sites per tetramer located at the interface between the subunits in each dimer [33]. One of the

• after the initial binding or due to communication between the two active sites in each dimer. In order to measure a Ki value for furan 17 the enzyme has to be allowed to reach its equilibrium in a competition between binding ThDP and binding the analogue, and then the level of residual activity will

• indicate the proportion of active sites that have ThDP bound. Therefore, ZmPDC was inactivated by furan 17 (1 µM) and then a large excess of ThDP (1 mM) was added and the recovery in activity was followed over 3 days. Some activity was slowly recovered (Figure 3) but this reached a plateau within 24 hours

Versatile synthesis of amino acid functionalized nucleosides via a domino carboxamidation reaction

• Vicky Gheerardijn,
• Jos Van den Begin and
• Annemieke Madder

Beilstein J. Org. Chem. 2014, 10, 2566–2572, doi:10.3762/bjoc.10.268

• have a stable and predictable structure allowing the design of engineered active sites through the carefully planned introduction of extra catalytic functionalities via solid phase DNA synthesis. We have further recently shown that the combination of solid phase synthesis and molecular modeling

• of histidine (imidazole) and lysine (cationic amine) are known to be present in numerous enzyme active sites and capable of general acid–general base catalysis, we have finally chosen to modify a nucleoside with a lysine amino acid derivative as a third example of our current strategy, as shown in

Carbohydrate PEGylation, an approach to improve pharmacological potency

• M. Eugenia Giorgi,
• Rosalía Agusti and
• Rosa M. de Lederkremer

Beilstein J. Org. Chem. 2014, 10, 1433–1444, doi:10.3762/bjoc.10.147

• products, depending on the number of lysine residues in the molecule. Random PEGylation may have undesired steric effects, shielding active sites in the protein or disrupting its tertiary structure [24]. PEGylation may be also directed to the side-chain amide nitrogen of Asn. In order to improve the

Synthesis of fluorescent (benzyloxycarbonylamino)(aryl)methylphosphonates

• Michał Górny vel Górniak,
• Anna Czernicka,
• Piotr Młynarz,
• Waldemar Balcerzak and
• Paweł Kafarski

Beilstein J. Org. Chem. 2014, 10, 741–745, doi:10.3762/bjoc.10.68

• carrying fluorescent probes in their side chains or in the ester phosphonate moieties might find an application in constructing fluorescent probes for studying structural requirements of enzymes having serine in their active sites (proteinases and phosphatases) or to study their elevated level in various

Conformation of dehydropentapeptides containing four achiral amino acid residues – controlling the role of L-valine

• Michał Jewgiński,
• Joanna Krzciuk-Gula,
• Maciej Makowski,
• Rafał Latajka and
• Paweł Kafarski

Beilstein J. Org. Chem. 2014, 10, 660–666, doi:10.3762/bjoc.10.58

• thermodynamically more stable and easier to obtain. As a consequence, the (Z)-isomers are much more common than the (E)-counterpart [19]. Dehydroamino acids contribute to a catalytic role in the active sites of some enzymes [20][21][22]. Additionally, the presence of these dehydrogenated analogues of amino acids is

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

Non-cross-linked polystyrene-supported 2-imidazolidinone chiral auxiliary: synthesis and application in asymmetric alkylation reactions

• Quynh Pham Bao Nguyen and
• Taek Hyeon Kim

Beilstein J. Org. Chem. 2013, 9, 2113–2119, doi:10.3762/bjoc.9.248

• result, polymer 3 with 50% active sites was balanced between the largest number of reactive sites and the most suitable solubility property of the polymer itself. N-Acylation of polymer 3 proceeded smoothly to yield polymers 5 in quantitative yields, as evidenced from the 1H NMR spectra of polymers 5

The application of a monolithic triphenylphosphine reagent for conducting Ramirez gem-dibromoolefination reactions in flow

• Kimberley A. Roper,
• Malcolm B. Berry and
• Steven V. Ley

Beilstein J. Org. Chem. 2013, 9, 1781–1790, doi:10.3762/bjoc.9.207

• macropores for flow through passage, in combination with a network of smaller mesopores to allow diffusion towards the active sites. This combined geometry has been shown to result in superior chemical efficiency over traditional supports by providing a shorter diffusion pathway to active sites via

Gallium-containing polymer brush film as efficient supported Lewis acid catalyst in a glass microreactor

• Rajesh Munirathinam,
• Roberto Ricciardi,
• Richard J. M. Egberink,
• Jurriaan Huskens,
• Michael Holtkamp,
• Herbert Wormeester,
• Uwe Karst and
• Willem Verboom

Beilstein J. Org. Chem. 2013, 9, 1698–1704, doi:10.3762/bjoc.9.194

• °C was needed to give the nitrile 8 in 82% [18]. Anthracen-9-carbaldehyde oxime (5, Table 2, entry 3) showed a relatively poor conversion, which is ascribed to the steric hindrance of the molecule in reaching the catalytically active sites within the polymer brushes. In literature [18] this reaction

A³-Coupling catalyzed by robust Au nanoparticles covalently bonded to HS-functionalized cellulose nanocrystalline films

• Jian-Lin Huang,
• Derek G. Gray and
• Chao-Jun Li

Beilstein J. Org. Chem. 2013, 9, 1388–1396, doi:10.3762/bjoc.9.155

• show lower catalytic activities compared with homogeneous catalysts, which may be caused by blocking the diffusion and adsorption of organic reactant molecules and products or the poor dispersion of active sites [22][23]. Cellulose nanocrystals (CNCs) have emerged as a new class of nanomaterials owing

• mol %. However, the activity slightly decreased with further increases in Au-loading up to 5.2 and 6.3 mol %. This decrease might be due to both the poor distribution of the Au active sites and the aggregation of the nanoparticles (See Figure S2, Supporting Information File 1). We determined the

Simple and rapid hydrogenation of p-nitrophenol with aqueous formic acid in catalytic flow reactors

• Rahat Javaid,
• Shin-ichiro Kawasaki,
• Akira Suzuki and
• Toshishige M. Suzuki

Beilstein J. Org. Chem. 2013, 9, 1156–1163, doi:10.3762/bjoc.9.129

• substrates, with which a much higher surface-area-to-volume ratio can be attained. The total amount of Pd present in the tube inner layer does not represent the concentration of active catalyst, since only surface metal atoms work as active sites. Therefore we estimated the number of surface Pd atoms using

Complete σ* intramolecular aromatic hydroxylation mechanism through O₂ activation by a Schiff base macrocyclic dicopper(I) complex

• Albert Poater and
• Miquel Solà

Beilstein J. Org. Chem. 2013, 9, 585–593, doi:10.3762/bjoc.9.63

• in mind the key role of dioxygen in biology, in particular toward Cu and Fe metal centers, being involved in the catalytic cycle of proteins, including dinuclear copper-active sites, such as hemocyanin, tyrosinase and catechol oxidases [1][2][3][4][5][6][7], either transporting or activating O2, its

Spin state switching in iron coordination compounds

• Philipp Gütlich,
• Ana B. Gaspar and
• Yann Garcia

Beilstein J. Org. Chem. 2013, 9, 342–391, doi:10.3762/bjoc.9.39

A chemist and biologist talk to each other about caged neurotransmitters

• Graham C.R. Ellis-Davies

Beilstein J. Org. Chem. 2013, 9, 64–73, doi:10.3762/bjoc.9.8

• active molecules to be synthesized with photochemically protecting groups at their active sites were nucleotides [1][2]. Two reports appeared in 1977 and 1978 describing the synthesis of ortho-nitrobenzyl derivatives of cyclic-AMP [1] and ATP [2]. The photolabile cAMP derivative was one member of a

The application of a monolithic triphenylphosphine reagent for conducting Appel reactions in flow microreactors

• Kimberley A. Roper,
• Heiko Lange,
• Anastasios Polyzos,
• Malcolm B. Berry,
• Ian R. Baxendale and
• Steven V. Ley

Beilstein J. Org. Chem. 2011, 7, 1648–1655, doi:10.3762/bjoc.7.194

• left on the monolith. This bromine could be present in hard-to-access active sites within the polymeric structure of the monolith, but could also be accounted for by some of the late intermediates in pathway B (10–15 in Scheme 1). The conversion of a particular substrate did not decrease with continued

Anion–π interactions influence pK_a values

• Christopher J. Cadman and
• Anna K. Croft

Beilstein J. Org. Chem. 2011, 7, 320–328, doi:10.3762/bjoc.7.42

• model systems and in enzyme active sites, in which the interacting species are brought in close proximity to one another, these effects are often amplified because of the reduction of the contribution of entropic factors. This is recognised as a proximity effect and can be measured by an effective

Stereoselectivity of supported alkene metathesis catalysts: a goal and a tool to characterize active sites

• Christophe Copéret

Beilstein J. Org. Chem. 2011, 7, 13–21, doi:10.3762/bjoc.7.3

• Abstract Stereoselectivity in alkene metathesis is a challenge and can be used as a tool to study active sites under working conditions. This review describes the stereochemical relevance and problems in alkene metathesis (kinetic vs. thermodynamic issues), the use of (E/Z) ratio at low conversions as a

• tool to characterize active sites of heterogeneous catalysts and finally to propose strategies to improve catalysts based on the current state of the art. Keywords: active sites; metathesis; stereoselectivity; supported catalysts; Introduction Achieving high selectivity and, in particular

• (styrenyl systems or alkenes with electron withdrawing substituents) [19][20][21]. Here the discussion will focus on the stereoselectivity of alkene metathesis in order to delineate the current state of the art in the case of heterogeneous catalysts and show how it can be used to characterize active sites

Flow through reactors for organic chemistry: directly electrically heated tubular mini reactors as an enabling technology for organic synthesis

• Ulrich Kunz and
• Thomas Turek

Beilstein J. Org. Chem. 2009, 5, No. 70, doi:10.3762/bjoc.5.70

• . We chose a polymer catalyst because polymers are well defined materials which can be functionalized easily with many active groups. This leads to a wide variety of materials, including composites, suitable as catalysts or for anchoring active sites leading to a large number of composites [17][18][19