Regioselectivity of glycosylation reactions of galactose acceptors: an experimental and theoretical study

• Enrique A. Del Vigo,
• Carlos A. Stortz and
• Carla Marino

Beilstein J. Org. Chem. 2019, 15, 2982–2989, doi:10.3762/bjoc.15.294

• in α-anomers could be associated with the lower capacity of the O-5 atom to establish hydrogen bond interactions due to the anomeric effect [34]. For donor 4, the regioselectivity observed for 1α, 1β, and 2α was lower than that observed for 3, but for 2β, the only product detected was the 1→4

• could be ascribed to the greater basicity of the O-ring of the β-anomers [34], which results in a stronger hydrogen bond OH-4⋅⋅⋅O-5. Although stronger interactions were observed for some of the conformers (Table S1, Supporting Information File 1), they corresponded to the less stable conformers

Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?

• Dominika Krištofíková,
• Juraj Filo,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290

• Bratislava, Mlynská dolina, Ilkovičova 6, 84215 Bratislava, Slovakia 10.3762/bjoc.15.290 Abstract A range of chiral hydrogen-bond-donating organocatalysts was tested in the Ireland–Claisen rearrangement of silyl ketene acetals. None of these organocatalysts was able to impart any enantioselectivity on the

• rearrangement, we tried to optimize its reaction course under mild conditions using various bases, solvents, and hydrogen-bond-donating catalysts. We also present a computational explanation and NMR kinetic study for the inefficient Ireland–Claisen rearrangement under thiourea and squaramide catalysis. Results

• was performed at 5 °C (Table 2, cf. entries 4 and 5) and the reaction temperature did not affect the diastereoselectivity of the reaction. No product 3c was obtained when the reaction was performed without silyl triflate (Table 2, entry 6). We assumed that hydrogen-bond-donating organocatalysts could

Palladium-catalyzed synthesis and nucleotide pyrophosphatase inhibition of benzo[4,5]furo[3,2-b]indoles

• Hoang Huy Do,
• Saif Ullah,
• Alexander Villinger,
• Joanna Lecka,
• Jean Sévigny,
• Peter Ehlers,
• Jamshed Iqbal and
• Peter Langer

Beilstein J. Org. Chem. 2019, 15, 2830–2839, doi:10.3762/bjoc.15.276

• . However, the zinc–metal interaction was exhibited by the substituted phenyl moiety on the indole ring. The oxygen atom of the furan ring of dual inhibitor 6e showed a single hydrogen bond with Phe548. Asp423 was found to be involved in two π–cation bindings with the indole ring, whereas π–π stacked, π–π T

Emission solvatochromic, solid-state and aggregation-induced emissive α-pyrones and emission-tuneable 1H-pyridines by Michael addition–cyclocondensation sequences

• Natascha Breuer,
• Irina Gruber,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 2684–2703, doi:10.3762/bjoc.15.262

• -pyridines 5 was further corroborated by a single crystal X-ray structure determination of compound 5a (Figure 1) [35]. In the single crystal the carboxyl ester group is oriented to the N–H and via a hydrogen bond. Solid-state torsional/dihedral angles between the 4- and 6-positioned aryl rings differ

Unexpected one-pot formation of the 1H-6a,8a-epiminotricyclopenta[a,c,e][8]annulene system from cyclopentanone, ammonia and dimethyl fumarate. Synthesis of highly strained polycyclic nitroxide and EPR study

• Sergey A. Dobrynin,
• Igor A. Kirilyuk,
• Yuri V. Gatilov,
• Andrey A. Kuzhelev,
• Olesya A. Krumkacheva,
• Matvey V. Fedin,
• Michael K. Bowman and
• Elena G. Bagryanskaya

Beilstein J. Org. Chem. 2019, 15, 2664–2670, doi:10.3762/bjoc.15.259

• distorted half-chair. Presumably, this difference is due to the formation of an intramolecular hydrogen bond O6–H…O5 (H…O 1.95(2) Å, O–H…O 154(2)°) in molecule 6. In the crystal of 1 the amino group participates in intermolecular hydrogen bonding N1–H…O3 (H…O 2.39(2) Å, N–H…O 167(1)°) forming chains of

Probing of local polarity in poly(methyl methacrylate) with the charge transfer transition in Nile red

• Aydan Yadigarli,
• Qimeng Song,
• Sergey I. Druzhinin and
• Holger Schönherr

Beilstein J. Org. Chem. 2019, 15, 2552–2562, doi:10.3762/bjoc.15.248

• anomalous fluorescence red shift of fluorophores in alcohols [44]. The additional red shift of NR in protic solvents, such as alcohols and probably chloroform, is associated with the hydrogen-bond formation with the carbonyl group of the dye [45]. The fluorescence maxima of NR in highly polarizable toluene

• substantial (53%) increase of the dipole moment upon excitation of NR. A clear deviation is observed for protic solvents and highly polarizable solvents (with n = 1.421−1.494) due to the different efficiency of hydrogen bond formation and contributions of inductive solute–solvent interactions in the ground

Anion-driven encapsulation of cationic guests inside pyridine[4]arene dimers

• Anniina Kiesilä,
• Jani O. Moilanen,
• Anneli Kruve,
• Christoph A. Schalley,
• Perdita Barran and
• Elina Kalenius

Beilstein J. Org. Chem. 2019, 15, 2486–2492, doi:10.3762/bjoc.15.241

• + formed complexes with 1 and 12, neither using electrospray ionization (ESI) in the positive nor the negative mode. Pr4N+ is certainly too large to fit inside the dimeric capsule, whereas the other non-complexing cations are protic and – as rather strong hydrogen-bond donors – may interfere with

• dispersion correction (hydrogen bond lengths are listed in Table S2, Supporting Information File 1). This is expected, because the standard hybrid functionals are able to describe strong hydrogen bonds such as NH···O and OH···O in a reasonable manner [31][32]. Due to the encapsulated guest molecule, the [12

• + Me4Nendo]+ complex has slightly longer NH···O and OH···O bonds than empty 12. The addition of I− anion(s) at the lower rim(s) of [12 + Me4Nendo]+ has hardly any influence on the length of NH···O and OH···O bonds as exemplified by the hydrogen bond lengths of [12 + Me4Nendo + Iexo] and [12 + Me4Nendo

Ultrafast processes triggered by one- and two-photon excitation of a photochromic and luminescent hydrazone

• Alessandro Iagatti,
• Baihao Shao,
• Alberto Credi,
• Barbara Ventura,
• Ivan Aprahamian and
• Mariangela Di Donato

Beilstein J. Org. Chem. 2019, 15, 2438–2446, doi:10.3762/bjoc.15.236

• the competition between the intramolecular hydrogen bond between the N–H and C=O groups in the Z-form and hydrogen bonds formed by these functional groups with solvent molecules. The conformational distortion and the increased conformational disorder arising from hydrogen bonding with the solvent can

Sugar-derived oxazolone pseudotetrapeptide as γ-turn inducer and anion-selective transporter

• Sachin S. Burade,
• Sushil V. Pawar,
• Tanmoy Saha,
• Navanath Kumbhar,
• Amol S. Kotmale,
• Manzoor Ahmad,
• Pinaki Talukdar and
• Dilip D. Dhavale

Beilstein J. Org. Chem. 2019, 15, 2419–2427, doi:10.3762/bjoc.15.234

• in the presence of valinomycin confirming the transport process occurring through an antiport mechanism via Cl−/NO3− exchange (Figure 8D). Such anion-selective transport can be rationalized based on the binding of anions with the terminal amino group of the transporter through hydrogen bond

Small anion-assisted electrochemical potential splitting in a new series of bistriarylamine derivatives: organic mixed valency across a urea bridge and zwitterionization

• Keishiro Tahara,
• Tetsufumi Nakakita,
• Alyona A. Starikova,
• Takashi Ikeda,
• Masaaki Abe and
• Jun-ichi Kikuchi

Beilstein J. Org. Chem. 2019, 15, 2277–2286, doi:10.3762/bjoc.15.220

• . Such N–H···F hydrogen-bond formation was also reported for other urea derivatives with PF6− as counteranion in the solid state [54][55]. The N···F distance of 2.85 Å in 1b+–PF6− is slightly longer than that observed in the crystal structure of a silver complex having a pyridyl urea ligand (2.67 and

Aggregation-induced emission effect on turn-off fluorescent switching of a photochromic diarylethene

• Luna Kono,
• Yuma Nakagawa,
• Ayako Fujimoto,
• Ryo Nishimura,
• Yohei Hattori,
• Toshiki Mutai,
• Nobuhiro Yasuda,
• Kenichi Koizumi,
• Satoshi Yokojima,
• Shinichiro Nakamura and
• Kingo Uchida

Beilstein J. Org. Chem. 2019, 15, 2204–2212, doi:10.3762/bjoc.15.217

• because the proton transfer occurs through an intramolecular hydrogen bond. This is also an origin of a large Stokes shift (8,000–11,000 cm−1) in the emission from the ESIPT state. Consequently, yellow luminescence was observed by UV-excitation [17][18]. Mutai et al. reported an ESIPT luminescence of an

Click chemistry towards thermally reversible photochromic 4,5-bisthiazolyl-1,2,3-triazoles

• Chenxia Zhang,
• Kaori Morinaka,
• Mahmut Kose,
• Takashi Ubukata and
• Yasushi Yokoyama

Beilstein J. Org. Chem. 2019, 15, 2161–2169, doi:10.3762/bjoc.15.213

• , differences can still be observed. In general, the thermal back reactions are faster in the more polar solvents, and faster in MeCN than in EtOH among these two solvents. However, for 2c, it is faster in EtOH than in MeCN. This may have originated from the hydrogen-bond formation between EtOH molecules and

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• selectivity of this receptor for chloride anion is due to the cavity size (see Figure 3) [37]. 2.2. Optical anion sensing by 1,2,3-triazolium macrocycles within porphyrin cages Various porphyrin-based host supramolecules containing hydrogen-bond donor groups such as integrated amide, urea, pyrrole, ammonium

• donors: The benefits of combining the triazolium motif with other hydrogen bond donor motifs has been explored by Sessler et al. and they have synthesized a pyrrole based tetra-1,2,3-triazolium macrocycle 10 (Figure 10) via the tetraalkylation of a triazole macrocycle originally prepared via click

• chemistry. Different hydrogen bond donors such as pyrrole N–H and benzene C–H along with the triazolium C5–H have been successfully incorporated within a single macrocyclic framework. The complex formation of anions with the hydrogen bond donors varied according to the polarity of the solvent. It was found

1,2,3,4-Tetrahydro-1,4,5,8-tetraazaanthracene revisited: properties and structural evidence of aromaticity loss

• Arnault Heynderickx,
• Sébastien Nénon,
• Olivier Siri,
• Vladimir Lokshin and
• Vladimir Khodorkovsky

Beilstein J. Org. Chem. 2019, 15, 2059–2068, doi:10.3762/bjoc.15.203

• ) and N–H···Cl (6a). The experimental (averaged) and calculated selected bond lengths are listed in Table 1. There are two independent molecules of 3 in the cell, bound with the short =N···H–N< hydrogen bond of 2.184 Å (Figure 2). Examination of the bond distances within the N2–C1–C14–C13–N12, N5–C6–C7

Synthesis of 1-azaspiro[4.4]nonan-1-oxyls via intramolecular 1,3-dipolar cycloaddition

• Yulia V. Khoroshunova,
• Denis A. Morozov,
• Andrey I. Taratayko,
• Polina D. Gladkikh,
• Yuri I. Glazachev and
• Igor A. Kirilyuk

Beilstein J. Org. Chem. 2019, 15, 2036–2042, doi:10.3762/bjoc.15.200

• nitroxides [26], implying free rotation of ethyl groups. In the EPR spectra in toluene the nitroxides 11a–c show 0.035–0.04 mT lower hfs constants on nitrogen atom compared to nitroxides 12a–c, presumably due to intramolecular hydrogen bond formation. The difference in aN between 11a–c and 12a–c is almost

Complexation of chiral amines by resorcin[4]arene sulfonic acids in polar media – circular dichroism and diffusion studies of chirality transfer and solvent dependence

• Bartosz Setner and
• Agnieszka Szumna

Beilstein J. Org. Chem. 2019, 15, 1913–1924, doi:10.3762/bjoc.15.187

• conclusion comes from a comparison of complexes in methanol and DMSO. One would expect that due to the dual hydrogen bond donor/acceptor character of methanol this solvent should be more destructive to ion-pair complexes based on charged hydrogen bonds than DMSO that can only serve as a hydrogen bond

Tautomerism as primary signaling mechanism in metal sensing: the case of amide group

• Vera Deneva,
• Georgi Dobrikov,
• Aurelien Crochet,
• Daniela Nedeltcheva,
• Katharina M. Fromm and
• Liudmil Antonov

Beilstein J. Org. Chem. 2019, 15, 1898–1906, doi:10.3762/bjoc.15.185

• can be seen that a hydrogen bond is formed between the nitrogen proton of one keto tautomer and the carbonyl group of another neighboring molecule. Probably, the process of associate formation is facilitated by the position of the chromophore part in the isolated K form (Figure 3, left). Obviously

• , based on 4-(phenyldiazenyl)naphthalen-1-ol. According to the theoretical calculations the enol form stabilization could be achieved through a strong intramolecular hydrogen bond formed between the tautomeric hydroxy group and the carbonyl group from the tautomeric backbone. However, intermolecular

Complexation of 2,6-helic[6]arene and its derivatives with 1,1′-dimethyl-4,4′-bipyridinium salts and protonated 4,4'-bipyridinium salts: an acid–base controllable complexation

• Jing Li,
• Qiang Shi,
• Ying Han and
• Chuan-Feng Chen

Beilstein J. Org. Chem. 2019, 15, 1795–1804, doi:10.3762/bjoc.15.173

• with larger counteranions of the guests and in less polar solvents. Furthermore, the switchable complexation between the helic[6]arene and protonated 4,4'-bipyridinium salt could be efficiently controlled by acids and bases. Keywords: 4,4'-bipyridinium salts; complexation; helic[6]arene; hydrogen bond

• protons of G1 and the aromatic rings of H1 with distances of 2.683 for A, 2.845 for B, 2.788 for C, 2.802 for D, and 2.868 Å for E, respectively. There also exist π–π stacking interactions between the pyridinium of G1 and the aromatic ring of H1 with the distance of 3.854 Å for F, a CH···O hydrogen bond

Water inside β-cyclodextrin cavity: amount, stability and mechanism of binding

• Stiliyana Pereva,
• Valya Nikolova,
• Silvia Angelova,
• Tony Spassov and
• Todor Dudev

Beilstein J. Org. Chem. 2019, 15, 1592–1600, doi:10.3762/bjoc.15.163

• /narrow belt) can be arranged in two alternative ways: (i) facing inward and creating a hydrogen-bond girdle (“head–tail” arrangement) that greatly decreases the size of the cavity vestibule (Figure 1A), and (ii) facing outward thus widening the aperture (“open” configuration, Figure 1B). Notably, in the

• “open” configuration the primary hydroxy groups do not participate in intramolecular hydrogen bond interactions. Relatively weak hydrogen bonds are formed between the secondary hydroxy groups in the wider/lower rim of the molecule. The calculations reveal that the “head–tail” arrangement of the narrow

• rim is the preferred mode of coordination (n = 2; Figure 2, structure a). In this construct the water dimer not only connects two oppositely located OH groups from the rim, but additionally interacts with four other OH groups and forms an elaborate hydrogen-bond network that almost occludes the

Synthesis and conformational preferences of short analogues of antifreeze glycopeptides (AFGP)

• Małgorzata Urbańczyk,
• Michał Jewgiński,
• Joanna Krzciuk-Gula,
• Jerzy Góra,
• Rafał Latajka and
• Norbert Sewald

Beilstein J. Org. Chem. 2019, 15, 1581–1591, doi:10.3762/bjoc.15.162

• the formation of an intramolecular hydrogen bond are characterized by chemical shifts that are independent on the temperature. When the amide proton is involved in a hydrogen bond, its temperature factor value is lower than 4.0 ppb/K [29][30]. Values of the measured temperature coefficient factors

• (see Table 1) suggest that the conformation of each of the investigated pentapeptides is stabilized by one hydrogen bond, created by the amide proton of Ala4. In the case of peptide 4 we could observe the strongest hydrogen bond (Table 1). Previous studies pointed out the role of specific hydrogen

• bonds between the peptide backbone and GalNAc moiety, which are responsible for creating the extended conformation [31][32]. However, further NMR investigations in this area found no evidence of an intramolecular hydrogen bond, or the existence of a very weak interaction, between the carbonyl group of

Enantioselective PCCP Brønsted acid-catalyzed aza-Piancatelli rearrangement

• Gabrielle R. Hammersley,
• Meghan F. Nichol,
• Helena C. Steffens,
• Jose M. Delgado,
• Gesine K. Veits and
• Javier Read de Alaniz

Beilstein J. Org. Chem. 2019, 15, 1569–1574, doi:10.3762/bjoc.15.160

• hydrogen bond group afforded the best selectivity (7k). To simplify the purification process, all acid products were transformed into the corresponding methyl ester in situ using (trimethylsilyl)diazomethane. A slight drop in enantioselectivity is observed when the benzoic acid group was moved to the meta

• furan ring required to initiate the cascade sequence. This highlights that a balance between nucleophilicity and hydrogen bond capabilities are required to obtain an efficient and selective reaction. Compared to the rearrangement of furylcarbinol 1a, sterically bulky aryl groups attached to the

A heteroditopic macrocycle as organocatalytic nanoreactor for pyrroloacridinone synthesis in water

• Piyali Sarkar,
• Sayan Sarkar and
• Pradyut Ghosh

Beilstein J. Org. Chem. 2019, 15, 1505–1514, doi:10.3762/bjoc.15.152

• environmentally oriented efficient organocatalysts with prominence “on-water conditions” [30][31]. It is known that an important condition for an organic reaction in water is the aggregation of the reactants and the catalyst by hydrophobic forces. Further, the potential of hydrogen-bond donation may be a vital

Synthesis and biological evaluation of truncated derivatives of abyssomicin C as antibacterial agents

• Leticia Monjas,
• Peter Fodran,
• Johanna Kollback,
• Carlo Cassani,
• Thomas Olsson,
• Maja Genheden,
• D. G. Joakim Larsson and
• Carl-Johan Wallentin

Beilstein J. Org. Chem. 2019, 15, 1468–1474, doi:10.3762/bjoc.15.147

• conformations and with expected interaction points in the binding site, providing suitable docking scores (see Supporting Information File 1). The key interactions include a hydrogen bond to the backbone of Arg-45 and lipophilic interactions in the deep pocket defined by Phe-241 and Leu-34 (Figure 2). Our

2,3-Dibutoxynaphthalene-based tetralactam macrocycles for recognizing precious metal chloride complexes

• Li-Li Wang,
• Yi-Kuan Tu,
• Huan Yao and
• Wei Jiang

Beilstein J. Org. Chem. 2019, 15, 1460–1467, doi:10.3762/bjoc.15.146

• parallel orientation. Three of the four NH protons are directed into the cavity, and the fourth one flipped outward and forms a hydrogen bond with the oxygen atom of H2O (H···O distance: 1.97 Å). Two CH3CN molecules were trapped in the cavities by the amide groups through N–H···N hydrogen bonds (H···N

Selenophene-containing heterotriacenes by a C–Se coupling/cyclization reaction

• Pierre-Olivier Schwartz,
• Sebastian Förtsch,
• Astrid Vogt,
• Elena Mena-Osteritz and
• Peter Bäuerle

Beilstein J. Org. Chem. 2019, 15, 1379–1393, doi:10.3762/bjoc.15.138

• (Figure 2b), because a completely flat geometry of the isolated molecule DST 3 (in the gas phase) was obtained from theoretical calculations (vide infra). Molecules of DST 3 order in a typical herringbone fashion, where the terminal hydrogen atoms form hydrogen bond-like C–H heteroatom interactions (2.819