Chiral phosphines in nucleophilic organocatalysis

• Yumei Xiao,
• Zhanhu Sun,
• Hongchao Guo and
• Ohyun Kwon

Beilstein J. Org. Chem. 2014, 10, 2089–2121, doi:10.3762/bjoc.10.218

• alkenes and MBH adducts, albeit in slightly diminished yields. Shi and co-workers also studied this reaction, but using the chiral bifunctional thiourea-phosphine catalyst G7. The [3 + 2] annulation of MBH carbonate with an activated isatin-based alkene in toluene at room temperature gave the

• . Using the bifunctional N-acylaminophosphine H5, Zhao and co-workers also achieved enantioselective [4 + 2] annulations of allenoates with N-tosylaldimines (Scheme 44) [85]. In the presence of 4 Å molecular sieves and with PhCF3 and CH2Cl2 as the mixed solvent, H5-catalzyed enantioselective [4 + 2

• ] annulations between α-substituted allenoates and N-tosylaldimines afforded a wide range of tetrahydropyridines in high yields and with good to excellent enantioselectivities. For some imines, the bifunctional phosphine displayed catalytic capability superior to that of Fu’s monophosphine system [84] in terms

Synthesis of a bifunctional cytidine derivative and its conjugation to RNA for in vitro selection of a cytidine deaminase ribozyme

• Nico Rublack and
• Sabine Müller

Beilstein J. Org. Chem. 2014, 10, 1906–1913, doi:10.3762/bjoc.10.198

• the aim of selecting a ribozyme for deamination of cytidine, we have set up a selection scheme involving the attachment of the cytidine acting as deamination substrate to the 3'-terminus of the RNAs in the library, and library immobilization. Here, we report the synthesis of a bifunctional cytidine

• bifunctionalized cytidine derivative and its successful conjugation to RNA. Results and Discussion Synthesis of the bifunctional cytidine derivative 1 started from uridine making use of four synthons: a protected hexaethylene glycol linker phosphoramidite 2 bearing a primary amine to be used later for RNA

• bifunctionalized cytidine derivative 1 as the final product was isolated by reversed-phase chromatography with a yield of 83% over the last three steps (Figure 6). To set-up conditions for conjugation of the bifunctional cytidine derivative 1 to RNA, we synthesized a short model oligonucleotide (GUC AGC CGU CAG

Comparing kinetic profiles between bifunctional and binary type of Zn(salen)-based catalysts for organic carbonate formation

• Carmen Martín and
• Arjan W. Kleij

Beilstein J. Org. Chem. 2014, 10, 1817–1825, doi:10.3762/bjoc.10.191

• was done between the binary catalyst system Zn(salphen)/NBu4I and a bifunctional system Zn(salpyr)·MeI with a built-in nucleophile. The latter system demonstrates an apparent second-order dependence on the bifunctional catalyst concentration and thus follows a different, bimetallic mechanism as

• [salphen = N,N’-phenylene-1,2-bis[salicylidene]imine] (Figure 1, 1) combined with a nucleophilic ammonium halide salt [26][27], or an analogous bifunctional system (Figure 1, 2) containing a Lewis acidic and nucleophilic center within the same molecule [29]. Mechanistic investigations for these CO2/epoxide

• (Figure 1) employed by Coates and first-order behavior in the case of the dinuclear Zn complex 8 (Figure 1). However, to the best of our knowledge, reports on comparative kinetic studies between structurally related binary and bifunctional systems are rare [43]. Herein we describe such a kinetic

Bifunctional dendrons for multiple carbohydrate presentation via carbonyl chemistry

• Davide Bini,
• Francesco Nicotra and
• Laura Cipolla

Beilstein J. Org. Chem. 2014, 10, 1686–1691, doi:10.3762/bjoc.10.177

Multichromophoric sugar for fluorescence photoswitching

• Stéphane Maisonneuve,
• Rémi Métivier,
• Pei Yu,
• Keitaro Nakatani and
• Juan Xie

Beilstein J. Org. Chem. 2014, 10, 1471–1481, doi:10.3762/bjoc.10.151

• -dicyanomethylene-2-tert-butyl-6-(p-dialkylaminostyryl)-4H-pyran) [3] with a photochromic diarylethene (DAE) which showed a photoreversible two-way FRET controlled by the state of the photochromic moiety, and 49% quenching of the fluorescence upon UV irradiation [4]. Bifunctional molecules built on two distinct

• (photochrome and fluorophore) moieties have also been reported by other groups [5][6][7][8][9]. The fluorophore vs photochrome ratio in reported bifunctional systems is 1:1 [4][5][6][7] or 2:1 [8][9]. Other strategies to assemble interacting fluorophores and photochromes (supramolecular systems, nanoparticles

• fluorescence photoswitching by energy transfer process (FRET). Bifunctional fluorescent-photochromic molecules 1 and 2. Absorption and fluorescence spectra of compounds 6, 9, and 2 in CH3CN: (a) absorption spectrum of 6; (b) emission spectrum of 6 (λexc = 450 nm); (c) absorption spectra of 9-OF, 9 at the

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

• been PEGylated and introduced in the surface of polystyrene nanoparticles in order to increase the interaction with galactose receptors. p-Aminophenyl β-D-galactopyranoside was coupled with a bifunctional PEG activated on one end with NHS for the combination with the aniline and a FMOC-protected amino

• with activated hydrophilic PEG to enhance its stability (Figure 5) [61]. Bifunctional PEGs were used to introduce a bioactive molecule, for instance biotine, coumarin, cholesterol or mannose into the distal end of a PEG-chitosan complex (Figure 6) [62]. Fructans have been PEGylated by reaction of

Rasta resin–triphenylphosphine oxides and their use as recyclable heterogeneous reagent precursors in halogenation reactions

• Xuanshu Xia and
• Patrick H. Toy

Beilstein J. Org. Chem. 2014, 10, 1397–1405, doi:10.3762/bjoc.10.143

• halogenation reactions With the versatility and excellent reactivity of 16 established, we were encouraged to examine our method in the epoxide halogenation reactions shown in Scheme 2. Since these reactions require the use of a base, we designed a bifunctional rasta resin, RR-NBniPr2-PPh3=O 18 (Scheme 5

• previously used as a bifunctional reagent in one-pot Wittig reactions [29]. Gel-phase 31P NMR spectroscopic analysis of 18 indicated that oxidation of the phosphine groups was complete, and elemental analysis was used to determine the loading level of phosphine oxide and amine groups to be 1.07 mmol/g and

• and 4), and alkyl substutients (Table 6, entries 5–8) all proceeded to completion, and afforded the corresponding 1,2-dihalides in excellent yields. We also examined the recyclability of 18 in the halogenation of epoxide 10C (Table 7). As was the case for 16, bifunctional polymer 18 could be

Molecular recognition of surface-immobilized carbohydrates by a synthetic lectin

• Melanie Rauschenberg,
• Eva-Corrina Fritz,
• Christian Schulz,
• Tobias Kaufmann and
• Bart Jan Ravoo

Beilstein J. Org. Chem. 2014, 10, 1354–1364, doi:10.3762/bjoc.10.138

• synthetic and natural lectins with the immobilized carbohydrates. To this end, bifunctional surfaces were fabricated by µCP of a the first ink in a dot pattern (10 μm dots spaced by a 5 μm gap) and filling up the interspaces with the second ink by using µCP with a flat stamp. In a first set of experiments

• black line shown in (A); (C) AFM height image of Glc ink and Gal ink cross printed in 5 μm stripes on an epoxide-terminated SAM; (D) Height profile of the black line shown in (C). Fluorescence images of bifunctional carbohydrate microarrays incubated with FITC-HisHis. (A) NANA (dots 10 × 5 μm) and Man

• (background); (B) Man (dots 10 × 5 μm) and NANA (background); (C) Gal (dots 10 × 5 μm) and Man (background); (D) Man (dots 10 × 5 μm) and Gal (background). Overlay of fluorescence images of bifunctional carbohydrate microarrays; (A) NANA (dots 10 × 5 μm) and Man (background) incubated with FITC-HisHis and

Glycosystems in nanotechnology: Gold glyconanoparticles as carrier for anti-HIV prodrugs

• Fabrizio Chiodo,
• Marco Marradi,
• Javier Calvo,
• Eloisa Yuste and
• Soledad Penadés

Beilstein J. Org. Chem. 2014, 10, 1339–1346, doi:10.3762/bjoc.10.136

• the release of the drug from the GNPs by enzymatic or pH mediated hydrolysis. 11-Mercaptoundecanoic acid was chosen as bifunctional aliphatic linker between the drugs and the gold nanoparticles. Aliphatic ester prodrugs of the anti-HIV drug zidovudine have previously shown to promote intestinal lymph

Human dendritic cell activation induced by a permannosylated dendron containing an antigenic GM₃-lactone mimetic

• Renato Ribeiro-Viana,
• Elena Bonechi,
• Javier Rojo,
• Clara Ballerini,
• Giuseppina Comito,
• Barbara Richichi and
• Cristina Nativi

Beilstein J. Org. Chem. 2014, 10, 1317–1324, doi:10.3762/bjoc.10.133

• strategies based on dendritic cells (DCs) armed with specific tumor antigens have been widely exploited due the properties of these immune cells in coordinating an innate and adaptive response. Here, we describe the convergent synthesis of the bifunctional multivalent glycodendron 5, which contains nine

• the convergent synthesis of the bifunctional multivalent glycodendron 5 (Scheme 1) and on human DC activation and related mixed-lymphocyte reaction (MLR) induced by the antigenic glycodendron 5. Results and Discussion Glycodendron 5 (Scheme 1) is a bifunctional compound containing nine residues of

• remove any trace of copper that could cause interferences in the biological assays. After purification by size exclusion chromatography by using a LH-20 column, the bifunctional glycodendron 5 was obtained in 86% yield and characterized by NMR and MS (electrospray). We tested in vitro human myeloid DCs

Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics

• Gijs Koopmanschap,
• Eelco Ruijter and
• Romano V.A. Orru

Beilstein J. Org. Chem. 2014, 10, 544–598, doi:10.3762/bjoc.10.50

• cyclic constrained peptidomimetics, the acyclic products have to be cyclized via additional cyclization strategies. This is possible via incorporation of bifunctional substrates into the initial IMCR. Examples of such bifunctional groups are N-protected amino acids, convertible isocyanides or MCR

• . the incorporation of bifunctional substrates or by activation of functionalized substrates in the initial MCR [19]. The Passerini reaction The first isocyanide-based MCR was described by Mario Passerini in 1921 and named after him. The Passerini reaction is a three-component reaction (3-CR) and

• -formation of the imine or the use of bifunctional inputs (e.g. amino acids) can reduce this Ugi-4CR to an Ugi-3CR. In particular, the Ugi reaction with bifunctional inputs is called an Ugi-four-center-three-component reaction (U-4C-3CR) and has been extensively applied in peptidomimetic synthesis [21][22

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• for Au NP, and these heterogeneous systems were tested as recyclable catalysts in an A3-coupling. The former was effective in three simple model reactions as a bifunctional catalyst (Au/acid) in aqueous medium at 70 °C. The latter works well in chloroform at 60 °C and tolerates a number of substituted

New hydrogen-bonding organocatalysts: Chiral cyclophosphazanes and phosphorus amides as catalysts for asymmetric Michael additions

• Helge Klare,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2014, 10, 224–236, doi:10.3762/bjoc.10.18

• hydrogen bonding. Mechanistic considerations We anticipated cyclodiphosphazane catalyst 14a to act as a bidentate bifunctional H-bond-donor catalyst. Therefore a conformation of the catalyst similar to the crystal structure but with an (exo/exo)-conformation is reasonable as otherwise a bidentate H-bonding

Oligomeric epoxide–amine adducts based on 2-amino-N-isopropylacetamide and α-amino-ε-caprolactam: Solubility in presence of cyclodextrin and curing properties

• Julian Fischer and
• Helmut Ritter

Beilstein J. Org. Chem. 2013, 9, 2803–2811, doi:10.3762/bjoc.9.315

• present paper we wish to describe our results about preparation and solubility of novel bio-based amine–epoxy oligoadducts. Also, we present some effects of CD on the solubility of these oligomers. Results and Discussion Generally, primary amins are bifunctional towards diepoxides and are thus monomers

Organocatalyzed enantioselective desymmetrization of aziridines and epoxides

• Ping-An Wang

Beilstein J. Org. Chem. 2013, 9, 1677–1695, doi:10.3762/bjoc.9.192

• . Cinchona alkaloid-derived catalysts OC-12 to OC-19. The chiral phosphoric acids catalysts OC-20 and OC-21. The proposed mechanism for chiral phosphorous acid-induced enantioselctive desymmetrization of meso-aziridines (chiral PA = OC-21). L-Proline and its derivatives OC-22 to OC-27. Proposed bifunctional

Organocatalytic asymmetric selenofunctionalization of tryptamine for the synthesis of hexahydropyrrolo[2,3-b]indole derivatives

• Qiang Wei,
• Ya-Yi Wang,
• Yu-Liu Du and
• Liu-Zhu Gong

Beilstein J. Org. Chem. 2013, 9, 1559–1564, doi:10.3762/bjoc.9.177

• ]. These leading findings indicate that either Lewis base or Brønsted acid shows catalytic activity for the selenofunctionalization reaction. Since chiral phosphoric acids have been shown to be Brønsted acid/Lewis base bifunctional organocatalysts [29][30][31][32][33], we ask whether the chiral BINOL-based

• basis of experimental observations, we proposed a reaction mechanism (Scheme 1). The phosphoric acid acts as a bifunctional catalyst and simultaneously activates both the tryptamine derivative and N-PSP by hydrogen-bonding interaction. Then, the asymmetric selenofunctionalization occurred at the 3

Electron self-exchange activation parameters of diethyl sulfide and tetrahydrothiophene

• Martin Goez and
• Martin Vogtherr

Beilstein J. Org. Chem. 2013, 9, 1448–1454, doi:10.3762/bjoc.9.164

• ]; both in acetonitrile versus SCE) the opposite order, even with a numerically similar difference, is calculated for the radical pair with D•+, although observations [28][29] that for bifunctional donors comprising both an amine and a sulfide moiety photoinduced electron transfer occurs exclusively from

Thiourea-catalyzed Diels–Alder reaction of a naphthoquinone monoketal dienophile

• Carsten S. Kramer and
• Stefan Bräse

Beilstein J. Org. Chem. 2013, 9, 1414–1418, doi:10.3762/bjoc.9.158

• ). At first, the use of MacMillan's imidazolidinone organocatalyst 6 [12] was examined, but no catalytic effect was observed (Table 2, entry 2). The usage of L-proline as a bifunctional catalyst only gave a slight improvement compared to the uncatalyzed reaction (Table 2, entry 3). Whereas the addition

Linkage of α-cyclodextrin-terminated poly(dimethylsiloxanes) by inclusion of quasi bifunctional ferrocene

• Helmut Ritter,
• Berit Knudsen and
• Valerij Durnev

Beilstein J. Org. Chem. 2013, 9, 1278–1284, doi:10.3762/bjoc.9.144

• structures of up to 400 nm. In the case of the complex of the compound 4 with ferrocene (Figure 5B), elongated structures of up to 4000 nm can be observed. This phenomenon might be explained by the supramolecular linkage of the short-chain disiloxanes by interaction with the bifunctional ferrocene molecules

• chloroform as solvent, by host–guest interactions of terminally attached α-CD with ferrocene as a quasi-bifunctional single guest molecule. The formation of noncovalent linkages was proved by the use of NMR spectroscopy and TEM images. However, it turned out that the stability of linking functions is

Isotopically labeled sulfur compounds and synthetic selenium and tellurium analogues to study sulfur metabolism in marine bacteria

• Nelson L. Brock,
• Christian A. Citron,
• Claudia Zell,
• Martine Berger,
• Irene Wagner-Döbler,
• Jörn Petersen,
• Thorsten Brinkhoff,
• Meinhard Simon and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2013, 9, 942–950, doi:10.3762/bjoc.9.108

• reduction of selenate and selenite to methaneselenol was tested by knockout of the genes for the bifunctional sulfate adenylyltransferase/adenylylsulfate kinase (cysC, strain WP73, locus tag PGA1_c24800) and the sulfite reductase (cysI, strain WP45, locus tag PGA1_c20760). No significant differences of the

Preparation and ring-opening reactions of N-diphenylphosphinyl vinyl aziridines

• Ashley N. Jarvis,
• Andrew B. McLaren,
• Helen M. I. Osborn and
• Joseph Sweeney

Beilstein J. Org. Chem. 2013, 9, 852–859, doi:10.3762/bjoc.9.98

• . Keywords: aziridines; catalytic; heterocycles; palladium; ring opening; Introduction Vinyl aziridines are useful molecules that have attracted the attention of synthetic chemists for many years. These strained bifunctional heterocycles possess considerable synthetic flexibility and undergo a range of

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

• the ligand field strength is too strong to meet the critical SCO condition. Replacement of one bifunctional phen ligand by two monofunctional NCS− ligands weakens the ligand field strength sufficiently to induce a thermal spin transition. Intraligand substitution

One-pot tandem cyclization of enantiopure asymmetric cis-2,5-disubstituted pyrrolidines: Facile access to chiral 10-heteroazatriquinanes

• Ping-An Wang,
• Sheng-Yong Zhang and
• Henri B. Kagan

Beilstein J. Org. Chem. 2013, 9, 265–269, doi:10.3762/bjoc.9.32

• 5a, 5b, 6a and 6b were also reported in [9], but our previously published structures for compounds 5a and 5b were not completely correct, because the B–N dative bonds were missing. The aim of the following procedures was to obtain several novel bifunctional N-hetereocyclic carbenes (NHCs) [10][11][12

Metal-mediated aminocatalysis provides mild conditions: Enantioselective Michael addition mediated by primary amino catalysts and alkali-metal ions

• Matthias Leven,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2013, 9, 155–165, doi:10.3762/bjoc.9.18

• ][13]. In most cases, transition or rare-earth metals are employed as Lewis acids in order to activate electrophilic compounds to react with substrates that are directly bonded to an organic catalyst [9][10][11][12][13]. An example is the enamine–metal Lewis acid bifunctional catalysis for asymmetric

Synthesis of a derivative of α-D-Glcp(1->2)-D-Galf suitable for further glycosylation and of α-D-Glcp(1->2)-D-Gal, a disaccharide fragment obtained from varianose

• Carla Marino,
• Carlos Lima,
• Karina Mariño and
• Rosa M. de Lederkremer

Beilstein J. Org. Chem. 2012, 8, 2142–2148, doi:10.3762/bjoc.8.241

• products indicates an inverting mechanism. Also lately, galactofuranosyl transferases (GalfT) catalyzing β-Galf incorporation in glycans have been identified. Two bifunctional GalfTs are required for galactan biosynthesis in Mycobacterium tuberculosis, GalfT1 and GalfT2, able to construct both, β-Galf(1→5