Conformational equilibrium in supramolecular chemistry: Dibutyltriuret case

• Karina Mroczyńska,
• Małgorzata Kaczorowska,
• Erkki Kolehmainen,
• Ireneusz Grubecki,
• Marek Pietrzak and
• Borys Ośmiałowski

Beilstein J. Org. Chem. 2015, 11, 2105–2116, doi:10.3762/bjoc.11.227

• some conditions: a) such a molecule must contain a hydrogen bond donor and acceptor in a close proximity and this is especially true when one assumes that b) a six-membered quasi-ring stabilized by hydrogen bonds is preferred over the five-membered one and that c) from the supramolecular/intermolecular

Synthesis of constrained analogues of tryptophan

• Elisabetta Rossi,
• Valentina Pirovano,
• Marco Negrato,
• Giorgio Abbiati and
• Monica Dell’Acqua

Beilstein J. Org. Chem. 2015, 11, 1997–2006, doi:10.3762/bjoc.11.216

• and 4). It is well known that reaction rates and selectivity in Diels–Alder reactions are affected by solvents [30][31][32]. In particular, polarity and hydrogen bond donor ability of the solvent can impact the diastereoisomeric ratios in a Diels–Alder reaction. Such an effect seems negligible in the

Derivatives of the triaminoguanidinium ion, 3. Multiple N-functionalization of the triaminoguanidinium ion with isocyanates and isothiocyanates

• Jan Szabo,
• Kerstin Karger,
• Nicolas Bucher and
• Gerhard Maas

Beilstein J. Org. Chem. 2014, 10, 2255–2262, doi:10.3762/bjoc.10.234

• transformations using heterocumulenes as reagents. Due to their particular molecular shape and the presence of hydrogen-bond donor and acceptor groups, the obtained 1,2,3-tris(ureido)guanidinium salts 7 and the derived neutral guanidine 8 may become of interest as host components in host–guest complexes, for

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

• the amino acid moiety providing a chiral environment and acting as a hydrogen bond donor while the phosphine unit functioned as the nucleophile. In the presence of 10 mol % of H1, they treated both cyclic and acyclic enones with the allenoates in toluene at −25 °C to generate corresponding

OligArch: A software tool to allow artificially expanded genetic information systems (AEGIS) to guide the autonomous self-assembly of long DNA constructs from multiple DNA single strands

• Kevin M. Bradley and
• Steven A. Benner

Beilstein J. Org. Chem. 2014, 10, 1826–1833, doi:10.3762/bjoc.10.192

• aggregation/folding motifs. With strength comparable to the G:C pair, AEGIS components form S:B, Z:P, V:J, and K:X pairs. (top) The conversion of S:B pairs to T:A pairs involves tautomerization of B to give its minor enol form, which present a hydrogen bond Donor–Acceptor–Donor pattern complementary to T. If

Streptopyridines, volatile pyridine alkaloids produced by Streptomyces sp. FORM5

• Ulrike Groenhagen,
• Michael Maczka,
• Jeroen S. Dickschat and
• Stefan Schulz

Beilstein J. Org. Chem. 2014, 10, 1421–1432, doi:10.3762/bjoc.10.146

• polyketide synthase gene cluster has not been identified yet. The streptazones are relatively small compounds suggesting that they may be volatile enough to find them in the headspace above bacterial cultures, although the presence of hydrogen bond donor and acceptor sites hints to good solubility in the

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

• of its hydrogen bonds: Computations of the hydrogen-bond-donor strength reveal a higher bonding energy to nitrobenzene (7.2 kcal/mol, Table 1) than for the comparable thiourea motif (6.5 kcal/mol). In terms of yields (Tables 2–4), the new phosphorusamide catalysts are competitive with standard HB

Stereoselectively fluorinated N-heterocycles: a brief survey

• Xiang-Guo Hu and
• Luke Hunter

Beilstein J. Org. Chem. 2013, 9, 2696–2708, doi:10.3762/bjoc.9.306

• group in a bioactive molecule with a fluorine atom can cause the loss of hydrogen bond donor ability, which may have profound effects on the ligand–receptor interaction. The study of fluorinated iminosugars serves as a good platform to discuss this issue. Naturally occurring iminosugars, also referred

• the treatment of type II diabetes. It was first marketed by Merck in 1996. The biological activity of the fluorinated analogues 35–37 (Figure 10) suggest that the C6 hydroxy group of 30 acts as a hydrogen bond donor in its binding to yeast α-glycosidase, while the C2' and C2 hydroxy groups of 30 do

Triol-promoted activation of C–F bonds: Amination of benzylic fluorides under highly concentrated conditions mediated by 1,1,1-tris(hydroxymethyl)propane

• Pier Alexandre Champagne,
• Alexandre Saint-Martin,
• Mélina Drouin and
• Jean-François Paquin

Beilstein J. Org. Chem. 2013, 9, 2451–2456, doi:10.3762/bjoc.9.283

• fluoride as a leaving group in nucleophilic substitution reactions of activated alkyl fluorides through hydrogen bonding [17]. Particularly, water was used as the hydrogen bond donor and co-solvent. DFT calculations show that activation proceeds through stabilization of the transition-state structure by

• completed with and without added triol 2 in order to establish its effect on the reactivity and results are reported in Table 1. In water or alcoholic solvent without added triol, low to moderate conversions were observed (12–26%). This was expected since these are all hydrogen bond-donor solvents [17][26

• ]. A low but quantifiable increase in conversion is observed when 2 is added to these reactions, with the best result (35%) being obtained in water (Table 1, entries 1–3). While the effect of the triol seems minimal, it is possible in these cases that 2, being both a hydrogen bond donor and acceptor

Synthesis and antibacterial activity of monocyclic 3-carboxamide tetramic acids

• Yong-Chul Jeong and
• Mark G. Moloney

Beilstein J. Org. Chem. 2013, 9, 1899–1906, doi:10.3762/bjoc.9.224

• )] under VG method, the hydrogen-bond donor count, the hydrogen-bond acceptor count, and the rotatable bond count. Antibacterial activity. Antibiotic activity was measured by using standard methodology (Clinical and Laboratory Standards Institute. Methods for antimicrobial susceptibility test for bacteria

Self-assembly of 2,3-dihydroxycholestane steroids into supramolecular organogels as a soft template for the in-situ generation of silicate nanomaterials

• Valeria C. Edelsztein,
• Andrea S. Mac Cormack,
• Matías Ciarlantini and
• Pablo H. Di Chenna

Beilstein J. Org. Chem. 2013, 9, 1826–1836, doi:10.3762/bjoc.9.213

• separately the hydrogen-bond donor (HBD, α), hydrogen-bond acceptor (HBA, β), and polarizability (π*) properties as contributions to the overall solvent polarity had also been occasionally used to study solvent–gelator specific interactions [20][21]. LMOGs based on cholesterol and bile acids offered the most

• either a strong hydrogen-bond donor or a strong hydrogen-bond acceptor, will significantly interact with the hydroxy groups of 1 and thus impede the supramolecular self-assembly and the formation of the gel. This way it will prevent gelation or will make a higher concentration of gelator necessary. This

• ) Hansen solubility parameters (δd dispersive interactions, δp dipolar interactions, δH hydrogen bonding) and b) Kamlet–Taft parameters (α hydrogen bond donor, β hydrogen bond acceptor, π* polarizability). Purple: gelated solvents. Red: non-gelated solvents. (For more details see Table S1 in Supporting

Use of 3-[¹⁸F]fluoropropanesulfonyl chloride as a prosthetic agent for the radiolabelling of amines: Investigation of precursor molecules, labelling conditions and enzymatic stability of the corresponding sulfonamides

• Reik Löser,
• Steffen Fischer,
• Achim Hiller,
• Martin Köckerling,
• Uta Funke,
• Aurélie Maisonial,
• Peter Brust and
• Jörg Steinbach

Beilstein J. Org. Chem. 2013, 9, 1002–1011, doi:10.3762/bjoc.9.115

• to this atom (H1C) it acts as a two-fold hydrogen-bond donor towards the sulfonyl oxygen (O1) of a neighbouring molecule with an O···H distance of 2.37(2) Å (N1···O1’: 3.015(2) Å) and an N–H···O angle of 142(2)° (Figure 2B). The second contact of the NH-group involves the fluorine atom (F1) of

Enantioselective reduction of ketoimines promoted by easily available (S)-proline derivatives

• Martina Bonsignore,
• Maurizio Benaglia,
• Laura Raimondi,
• Manuel Orlandi and
• Giuseppe Celentano

Beilstein J. Org. Chem. 2013, 9, 633–640, doi:10.3762/bjoc.9.71

• , reported by Zhang [16][17] and intensely studied by our group [18][19][20][21][22][23], the presence of the acidic hydrogen of the amide group is essential for the stereochemical efficiency of the metal-free catalyst. Based on these considerations we decided to investigate the use of a strong hydrogen-bond

• donor functionality as the carboxylic acid group; it is worth mentioning that also phosphoric acid catalyzed reductions of C=N bonds with Hantzsch ester involve the coordination and activation of the substrate through the formation of a H-bond between the hydrogen atom of the phosphoric acid and the

Asymmetric desymmetrization of meso-diols by C₂-symmetric chiral 4-pyrrolidinopyridines

• Hartmut Schedel,
• Keizo Kan,
• Yoshihiro Ueda,
• Kenji Mishiro,
• Keisuke Yoshida,
• Takumi Furuta and
• Takeo Kawabata

Beilstein J. Org. Chem. 2012, 8, 1778–1787, doi:10.3762/bjoc.8.203

• carbonyl groups at C(2) and C(5) seem to play the key role in the asymmetric desymmetrization of 5 to give (1R,2S)-6 (Table 1 and Table 4), we assume that the amide carbonyl group would serve as a hydrogen-bond acceptor and the non-reacting OH of 5 as a hydrogen-bond donor. A possible approach of substrate

• molecular modeling study. It is also anticipated that an axial-OH may be the better hydrogen-bond donor than an equatorial-OH, according to the reported higher acidity of the axial hydroxy groups of cyclohexane derivatives [39]. An alternative model for the transition-state assembly is shown in Figure 3

• where the amide NH group of A serves as a hydrogen-bond donor and the non-reacting OH of substrate 5 as a hydrogen-bond acceptor. This model could explain the difference between effective catalyst 11 and ineffective catalysts 15 and 16 (Table 4, entry 1 vs entries 2 and 3). However, the calculated

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

• hydrogen-bond acceptor binding of 2-F-maltose is impaired due to the hydrogen-bond donor activity of the 2-OH group (to the carboxylate of Glu111). In that respect, introducing the fluorine into the 6-position results in a smaller energetic penalty (compared to the 2-F-maltose), because no direct H-bonds

NMR studies of anion-induced conformational changes in diindolylureas and diindolylthioureas

• Damjan Makuc,
• Jennifer R. Hiscock,
• Mark E. Light,
• Philip A. Gale and
• Janez Plavec

Beilstein J. Org. Chem. 2011, 7, 1205–1214, doi:10.3762/bjoc.7.140

• heterocycles, such as carbazole, 2,2'-biindole and indolo[1,2-b]carbazoles, have recently attracted significant attention [24][25][26][27][28][29][30][31]. Indole contains a single hydrogen bond donor group, which is employed in biological systems to bind anions such as chloride [32] and sulfate [14]. We have

• molecules for the hydrogen bond donor groups of the receptor, and the weak basicity of the chloride. This is supported by the stability constant determinations previously reported, and presented in Table 1. Considerable downfield shifts of δH7α were observed upon addition of acetate, benzoate and

• -anions interact both with H1 and H7α due to their Y-shaped geometry. The tetrahedral geometry of the dihydrogen phosphate anion allows strong interaction with all four hydrogen bond donor groups, which is reflected in the substantial deshielding of the H1 and H7α protons (Figure 2f). Interestingly, one

A practical two-step procedure for the preparation of enantiopure pyridines: Multicomponent reactions of alkoxyallenes, nitriles and carboxylic acids followed by a cyclocondensation reaction

• Christian Eidamshaus,
• Roopender Kumar,
• Mrinal K. Bera and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2011, 7, 962–975, doi:10.3762/bjoc.7.108

• , whereas the pyridinol tautomer is favored when a hydrogen bond-donor is present. Compound 37 exists exclusively as pyridone tautomer, but after desilylation the resulting product, with a free hydroxy group in the side chain, strongly prefers the pyridinol tautomer. It seems reasonable to assume that the

Stereogenic boron in 2-amino-1,1-diphenylethanol-based boronate–imine and amine complexes

• Sebastian Schlecht,
• Walter Frank and
• Manfred Braun

Beilstein J. Org. Chem. 2011, 7, 615–621, doi:10.3762/bjoc.7.72

• the nitrogen from sp2 to sp3. The structure determination 10·CH3OH reveals a hydrogen bridge of the amine hydrogen atom directed to the oxygen atom of the alcohol. The fact that the NH group functions as the hydrogen-bond donor is attributed to an enhanced acidity that is caused by the coordinate bond

Oxalyl retro-peptide gelators. Synthesis, gelation properties and stereochemical effects

• Janja Makarević,
• Milan Jokić,
• Leo Frkanec,
• Vesna Čaplar,
• Nataša Šijaković Vujičić and
• Mladen Žinić

Beilstein J. Org. Chem. 2010, 6, 945–959, doi:10.3762/bjoc.6.106

• units with specifically oriented hydrogen bond donor and acceptor sites and amino acid lipophilic substituents. Such structural characteristics enable multiple structural and stereochemical variations of the basic gelator structure and subsequent studies of structural and stereochemical influences on

Chain stopper engineering for hydrogen bonded supramolecular polymers

• Thomas Pinault,
• Bruno Andrioletti and
• Laurent Bouteiller

Beilstein J. Org. Chem. 2010, 6, 869–875, doi:10.3762/bjoc.6.102

• analogue of the bis-urea monomer is shown not to form a supramolecular polymer, but a good chain stopper, because it is a strong hydrogen bond donor and a weak acceptor. Moreover, all substituted ureas tested reduce the viscosity of the supramolecular polymer solutions, but the best chain stopper is

• obtained when two hydrogen bond acceptors are placed in the same relative position as for the monomer and when no hydrogen bond donor is present. Keywords: chain stopper; gel; hydrogen bond; supramolecular polymer; urea; Introduction Supramolecular polymers are linear chains of low molar mass monomers

• assemblies as a hydrogen bond donor. For this purpose, we synthesized the bis-thiourea S4, from the corresponding bis-thioisocyanate, because thioureas are known to be strong hydrogen bond donors and weak hydrogen bond acceptors [34][35]. Before evaluating the chain stopper efficiency of these compounds, i.e

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

• important parameter for polymers, which indicates the transition of the amorphous phase of the polymer from its rubbery to its glassy state (and vice versa). Pure PVAm shows a Tg of 103 °C. The glass transition temperature is a function of chain flexibility. Because of the presence of hydrogen-bond donor

• interactions (hydrogen bonding), we used the simplified Kamlet–Taft equation (Equation 1) [45][46]. According to Equation 1, the influence of the hydrogen-bond donor capacity (HBD) [47], the hydrogen-bond acceptor capacity (HBA) [48] and the dipolarity/polarizability [45][49] of a solvent can be expressed by α

Anion receptors containing thiazine-1,1-dioxide heterocycles as hydrogen bond donors

• Hong-Bo Wang,
• James A. Wisner and
• Michael C. Jennings

Beilstein J. Org. Chem. 2010, 6, No. 50, doi:10.3762/bjoc.6.50

• of nitrogen-based hydrogen bond donor groups such as amides [3][4], ureas [5], pyrroles/indoles/carbazoles [6][7] and sulfonamides [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] to complex the anionic targets in a topologically complementary fashion. Sulfonamides are an interesting

• case as the hydrogen bond donor is often significantly more acidic (pKa approx. 11 for simple N-phenylaryl sulfonamides such as 3 (see below)) than that presented by other groups typically incorporated in these frameworks. The greater acidity of such a subunit can be an advantage by providing greater

• potential hydrogen bond donor strength with anionic guests. Alternatively, the possibility of deprotonation in some specific systems by basic anions such as carboxylates or fluoride can be employed as an indicator for these species. Regardless, the incorporation of sulfonamide functional groups has

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

• bonds such as dimethylsulfoxide, a very good hydrogen bond acceptor, and water, which is a poorer hydrogen bond acceptor than methanol, but very good hydrogen bond donor. Solvents competing in the intermolecular bond formation result in lower binding constants. Additionally, the binding ability is

Synthesis of indolo[3,2-b]carbazole-based new colorimetric receptor for anions: A unique color change for fluoride ions

• Ajit Kumar Mahapatra,
• Giridhari Hazra and
• Prithidipa Sahoo

Beilstein J. Org. Chem. 2010, 6, No. 12, doi:10.3762/bjoc.6.12

• Ajit Kumar Mahapatra Giridhari Hazra Prithidipa Sahoo Department of Chemistry, Bengal Engineering and Science University, Shibpur, Howrah 711103, India, Tel.: +91 33 2668 4561; Fax: +91 33 2668 4564 10.3762/bjoc.6.12 Abstract A novel indolocarbazole-based chemosensor 1 containing hydrogen bond

• donor moieties has been established as a selective colorimetric and fluorometric sensor for F− in CH3CN/H2O (4:1 v/v). Upon the addition of a series of tetrabutylammonium salts to receptor 1 in aqueous CH3CN, only when the counter ion was F− was a significant color change (from light violet to dark

Synthesis and binding studies of two new macrocyclic receptors for the stereoselective recognition of dipeptides

• Ana Maria Castilla,
• M. Morgan Conn and
• Pablo Ballester

Beilstein J. Org. Chem. 2010, 6, No. 5, doi:10.3762/bjoc.6.5

• = hydrogen bond donor, A = hydrogen bond acceptor) instead of ADAD when just one methylene group spans the two amide groups (ΔΔG0 (malonamide-Gly) = −0.96 kcal/mol). In contrast, parallel receptor 2 effectively discriminates in favor of the hydrogen-bonding pattern ADDA when two methylene groups span the