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

• , 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

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

• “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

• evaluated at the M062X/6-311++G(d,p)//M062X/6-31G(d,p) level of theory (Supporting Information File 1, Table S1). As a general trend, it was observed that expanding the intramolecular hydrogen bond network upon each H2O addition (comprising the water–water and water–cyclodextrin interactions) enhances 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

• 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

• determined, no predominant conformer was found. As shown in Figure 3A and B both tripeptides indicate a fully flexible conformation. Corzana et al. suggested for the C- and N-protected, glycosylated ʟ-serine residue an extended conformation without intramolecular hydrogen bond between the amide proton of

Catalytic asymmetric oxo-Diels–Alder reactions with chiral atropisomeric biphenyl diols

• Chi-Tung Yeung,
• Wesley Ting Kwok Chan,
• Wai-Sum Lo,
• Ga-Lai Law and
• Wing-Tak Wong

Beilstein J. Org. Chem. 2019, 15, 955–962, doi:10.3762/bjoc.15.92

• biphenyl ring intact. Relative spatial arrangement of the larger phenyl substituent is located at the side where it is relatively far away from the intramolecular hydrogen bond unit. Catalytic studies With the organocatalyst 1 in hand, we firstly examined the oxo-DA reaction of benzaldehyde and Rawal’s

Study on the regioselectivity of the N-ethylation reaction of N-benzyl-4-oxo-1,4-dihydroquinoline-3-carboxamide

• Pedro N. Batalha,
• Luana da S. M. Forezi,
• Maria Clara R. Freitas,
• Nathalia M. de C. Tolentino,
• Ednilsom Orestes,
• José Walkimar de M. Carneiro,
• Fernanda da C. S. Boechat and
• Maria Cecília B. V. de Souza

Beilstein J. Org. Chem. 2019, 15, 388–400, doi:10.3762/bjoc.15.35

• structure that the intramolecular hydrogen bond between the hydrogen of the amide group, CON–H, and the carbonyl oxygen (C-4), promotes coplanarity between the oxoquinoline nucleus and the CONH moiety of this amide group connected to C-3, as expected. An additional crystallographic description and the full

1,8-Bis(dimethylamino)naphthyl-2-ketimines: Inside vs outside protonation

• A. S. Antonov,
• A. F. Pozharskii,
• P. M. Tolstoy,
• A. Filarowski and
• O. V. Khoroshilova

Beilstein J. Org. Chem. 2018, 14, 2940–2948, doi:10.3762/bjoc.14.273

• for 4a, while the E-form is more stable for 5a–7a. Indeed, the X-ray analysis shows that compound 6a in the solid state exists in the E-form stabilised by the N−H···O intramolecular hydrogen bond (IHB) with an ortho-OMe group (Figure 2a), while compound 4a, as it was revealed in our previous work [7

• , signals are coalescent even at −80 °C (Figure 7). The presence of an OMe group in the ortho-position to C=N groups in 5c slows down the exchange and results in NH2+ signals splitting at −40 °C. This can be attributed to the formation of the weak NHO intramolecular hydrogen bond, which becomes stronger

Green synthesis of new chiral 1-(arylamino)imidazo[2,1-a]isoindole-2,5-diones from the corresponding α-amino acid arylhydrazides in aqueous medium

• Nadia Bouzayani,
• Jamil Kraїem,
• Sylvain Marque,
• Yakdhane Kacem,
• Abel Carlin-Sinclair,
• Jérôme Marrot and
• Béchir Ben Hassine

Beilstein J. Org. Chem. 2018, 14, 2923–2930, doi:10.3762/bjoc.14.271

• between H(1) and H(4) in the NOE experiment. The structure contains two carbonyl moieties C(6)–O(2) and C(3)–O(1) with similar distances of 1.222 and 1.218 Å, respectively. The intramolecular hydrogen bond O(1)–H(13) remains strong in the nitrogenated tricycle (2.579 Å) vis-à-vis of the starting hydrazide

• imino-carboxylic acid form likely evolves to its iminium-carboxylate form B [50]. This last intermediate involves the existence of two possible transition states for the cyclization of the imidazolidinone core of which one of them is favored by an intramolecular hydrogen bond (Scheme 5). This control is

Synthesis of dihydroquinazolines from 2-aminobenzylamine: N³-aryl derivatives with electron-withdrawing groups

• Nadia Gruber,
• Jimena E. Díaz and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2018, 14, 2510–2519, doi:10.3762/bjoc.14.227

• . Such effect would result from an intramolecular hydrogen bond between the ammonium and nitro groups in the reaction intermediate, also known as “built-in solvation” [71] (Figure 2). When 2-ABA was reacted with 2-chloro-3-nitropyridine (CNP) in analogous experimental conditions as 2a, compound 2c was

Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

• Alex Frichert,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

• appeared as a sharp signal at 5.25 ppm (CDCl3) for 29 and as a broad peak at 3.00 ppm for 30. This can be explained by the presence of an intramolecular hydrogen bond that is possible only in the case of 29. Since the 1H NMR spectrum of cyanohydrin 22 exhibits a sharp hydroxy peak at 5.29 ppm, we derive

First thia-Diels–Alder reactions of thiochalcones with 1,4-quinones

• Grzegorz Mlostoń,
• Katarzyna Urbaniak,
• Paweł Urbaniak,
• Anna Marko,
• Anthony Linden and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2018, 14, 1834–1839, doi:10.3762/bjoc.14.156

• centrosymmetric, the compound in the crystal is racemic. The S-atom of the thiophene ring is disordered over two unequally occupied positions as a result of slight but opposite directions of envelope puckering of the ring. The hydroxy group forms an intramolecular hydrogen bond with the adjacent quinoid O-atom

The use of 4,4,4-trifluorothreonine to stabilize extended peptide structures and mimic β-strands

• Yaochun Xu,
• Isabelle Correia,
• Tap Ha-Duong,
• Nadjib Kihal,
• Jean-Louis Soulier,
• Julia Kaffy,
• Benoît Crousse,
• Olivier Lequin and
• Sandrine Ongeri

Beilstein J. Org. Chem. 2017, 13, 2842–2853, doi:10.3762/bjoc.13.276

• pentapeptide salts 1b–4b were obtained in quantitative yield. Conformational studies. The conformational properties of the eight pentapeptides (1a–4a and 1b–4b) were examined by NMR analyses in a protic solvent, which is more challenging than in aprotic organic solvents for maintaining intramolecular hydrogen

• bond network. Methanol was used because of the limited solubility of these compounds in aqueous solutions. The 1H and 13C chemical shifts of these pentapeptides were assigned using 1D 1H, 2D 1H,1H-TOCSY, 2D 1H,1H-ROESY, 2D 1H,13C-HSQC, and 2D 1H,13C-HMBC spectra. The 1H and 13C chemical shift

Pyrene–nucleobase conjugates: synthesis, oligonucleotide binding and confocal bioimaging studies

• Artur Jabłoński,
• Yannic Fritz,
• Hans-Achim Wagenknecht,
• Rafał Czerwieniec,
• Tytus Bernaś,
• Damian Trzybiński,
• Krzysztof Woźniak and
• Konrad Kowalski

Beilstein J. Org. Chem. 2017, 13, 2521–2534, doi:10.3762/bjoc.13.249

• /C17/C18/O26 atoms and non-hydrogen atoms of the pyrenyl group are inclined by an angle of 17.26(5)°. The carbonyl oxygen atom O26 is involved in the intramolecular hydrogen bond with the hydrogen atom H3 of the pyrenyl group. The C3–H3···O26 hydrogen bond length is 2.879(2) Å. In the solid state, each

Dialkyl dicyanofumarates and dicyanomaleates as versatile building blocks for synthetic organic chemistry and mechanistic studies

• Grzegorz Mlostoń and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 2235–2251, doi:10.3762/bjoc.13.221

• yields. The X-ray analysis showed that products 53 obtained with primary amines are Z-configured whereas those derived from secondary amines, 54, display E-configuration [58] (Scheme 18). The observed different configurations demonstrate the importance of the intramolecular hydrogen-bond between the NH

Complexation of molecular clips containing fragments of diphenylglycoluril and benzocrown ethers with paraquat and its derivatives

• Leonid S. Kikot',
• Catherine Yu. Kulygina,
• Alexander Yu. Lyapunov,
• Svetlana V. Shishkina,
• Roman I. Zubatyuk,
• Tatiana Yu. Bogaschenko and
• Tatiana I. Kirichenko

Beilstein J. Org. Chem. 2017, 13, 2056–2067, doi:10.3762/bjoc.13.203

• , the intramolecular hydrogen bonds with participation of the carbonyl oxygen atom which are typical for complexes 2@9 and 3@9 are not formed. In complex 2@10 one hydroxy group forms an intramolecular hydrogen bond with a polyether oxygen atom of the clip (О–H···O, O···O, О–H···O, 2.29, 2.99 Å, 141

Conformational impact of structural modifications in 2-fluorocyclohexanone

• Francisco A. Martins,
• Josué M. Silla and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2017, 13, 1781–1787, doi:10.3762/bjoc.13.172

• as Y, which exhibit intramolecular hydrogen bond with the equatorial fluorine) show axial prevalence. On the other hand, the equatorial conformer is preferred when X = S and NHeq (except for Y = NHE). While the axial preference for compounds with X = NHax can be determined by an electrostatic

• , dipolar relaxation F···HaxN (since an intramolecular hydrogen bond has not been clearly demonstrated in 3-fluoropiperidine [7][8][9][10][11][12][13]), such behavior for compounds with X = CH2 seems to be dependent on the C=Y bond, since X = CH2 is not a good proton donor. In this case, the axial

• hydrogen bond F···HN (e.g., dF···HN = 2.21 Å and F···H–N angle = 110.0°, when X/Y = CH2/NHZ), despite similar interactions hardly ever appear in organofluorine compounds when forming 5-membered rings [25][26]. In addition, it is also quite intuitive that fluorine tends to occupy the axial orientation in

Switchable highly regioselective synthesis of 3,4-dihydroquinoxalin-2(1H)ones from o-phenylenediamines and aroylpyruvates

• Juraj Dobiaš,
• Marek Ondruš,
• Gabriela Addová and
• Andrej Boháč

Beilstein J. Org. Chem. 2017, 13, 1350–1360, doi:10.3762/bjoc.13.132

• of the studied derivatives [4][5]. In this case, their tautomeric equilibrium is shifted to enamines 3 that have been stabilized by an intramolecular hydrogen bond (Scheme 1). A new pseudo-ring is formed via the hydrogen bond in 3, which further spreads the planarity of the 3,4-dihydroquinoxalin-2(1H

• crystallisation from DMSO, pure 16d (SYN) was isolated. We elucidated its structure in similar manner as for the 17d (ANTI) isomer (Figure 2) and confirmed that the 1H NMR (DMSO-d6) higher shifted signal for the H-N(4) group is the one that forms a intramolecular hydrogen bond with the carbonyl group from a side

• -dihydroquinoxaline-2(1H)-ones. Their ANTI (17) or SYN (16) structures were assigned by complex 2D NMR techniques (HSQC, NOESY and HMBC) or by a proposed simplified method (NOE interaction between higher 1H NMR (DMSO-d6) shifted H-N(4), bonded by intramolecular hydrogen bond, and H-C(5) or interaction of lower

Synthesis of tetrasubstituted pyrazoles containing pyridinyl substituents

• Josef Jansa,
• Ramona Schmidt,
• Ashenafi Damtew Mamuye,
• Laura Castoldi,
• Alexander Roller,
• Vittorio Pace and
• Wolfgang Holzer

Beilstein J. Org. Chem. 2017, 13, 895–902, doi:10.3762/bjoc.13.90

• 2a,b, 3a,b and 4a,b) strongly hints to the involvement of the former into an intramolecular hydrogen bond as indicated in Scheme 3. Cross-coupling reactions Initial attempts to react 4-bromopyrazole 5 – obtained from reaction of 2a with N-bromosuccinimide – with phenylboronic acid (or 3

Spectral and DFT studies of anion bound organic receptors: Time dependent studies and logic gate applications

• Srikala Pangannaya,
• Neethu Padinchare Purayil,
• Shweta Dabhi,
• Venu Mankad,
• Prafulla K. Jha,
• Satyam Shinde and
• Darshak R. Trivedi

Beilstein J. Org. Chem. 2017, 13, 222–238, doi:10.3762/bjoc.13.25

• gain insight into the binding mechanism, 1H NMR titration studies have been performed with the incremental addition of TBAOAc to a DMSO-d6 solution of receptor R1 and R2. The unbound receptor exhibited a OH proton signal at ~14 ppm due to the presence of an intramolecular hydrogen bond interaction with

The aminoindanol core as a key scaffold in bifunctional organocatalysts

• Isaac G. Sonsona,
• Eugenia Marqués-López and
• Raquel P. Herrera

Beilstein J. Org. Chem. 2016, 12, 505–523, doi:10.3762/bjoc.12.50

• catalyst, in its Z form, which is stabilized due to an intramolecular hydrogen bond (Scheme 14). In 2012, Dong and co-workers studied the catalytic activity of several β-amino alcohol-based squaramide organocatalysts involved in the Michael addition of acetylacetone (36a) to β-nitrostyrene (3a) in

Friedel–Crafts-type reaction of pyrene with diethyl 1-(isothiocyanato)alkylphosphonates. Efficient synthesis of highly fluorescent diethyl 1-(pyrene-1-carboxamido)alkylphosphonates and 1-(pyrene-1-carboxamido)methylphosphonic acid

• Anna Wrona-Piotrowicz,
• Janusz Zakrzewski,
• Anna Gajda,
• Tadeusz Gajda,
• Anna Makal,
• Arnaud Brosseau and
• Rémi Métivier

Beilstein J. Org. Chem. 2015, 11, 2451–2458, doi:10.3762/bjoc.11.266

• approximately two-fold increase in solution fluorescence quantum yield in comparison with that of a model N-alkyl pyrene-1-carboxamide. This effect was tentatively explained by stiffening of the amidophosphonate lateral chain which was caused by the interaction (intramolecular hydrogen bond) of phosphonate and

• of an intramolecular hydrogen bond between the N–H and P=O groups (Figure 4), which also leads to stiffening of the lateral chain and to blocking the non-radiative deactivation channel. The presence of such a bond was verified via variable concentration 1H NMR spectroscopy [33], which showed only

• emission (b) spectra of 3a in various solvents. Fluorescence decay curves for 3a and 5 in chloroform and for 4 in 0.01 M PBS (pH 7.35). λexcit = 360 nm; λem = 385, 390 and 383 nm, respectively. Intramolecular hydrogen bond in 3a–d. Normalized electronic absorption (violet) and emission (pink) spectrum of

2-Hetaryl-1,3-tropolones based on five-membered nitrogen heterocycles: synthesis, structure and properties

• Yury A. Sayapin,
• Inna O. Tupaeva,
• Alexandra A. Kolodina,
• Eugeny A. Gusakov,
• Vitaly N. Komissarov,
• Igor V. Dorogan,
• Nadezhda I. Makarova,
• Anatoly V. Metelitsa,
• Valery V. Tkachev,
• Sergey M. Aldoshin and
• Vladimir I. Minkin

Beilstein J. Org. Chem. 2015, 11, 2179–2188, doi:10.3762/bjoc.11.236

• diffraction. 2-(2-Benzoxa(thia)zolyl)-6-alkoxycarbonylphenols display intense green fluorescence with anomalous Stokes shifts caused by the excited state intramolecular proton transfer (ESIPT) effects. Keywords: β-tropolones; fluorescence; intramolecular hydrogen bond; tautomerism; X-ray analysis

• )–С(2)–С(3) is equal to 1.5°. The intramolecular hydrogen bond in the cycle N(1)–С(8)–С(2)–С(3)–О(2)–Н(2) is characterized by the distances N(1)···О(2) = 2.599(4), N(1)···Н(2) = 1.830(6) Å and the angle N(1)–H(2)–O(2) of 150.4(9)°. The proton signals of the hydroxy groups of 11 (R1 = H) and 11 (R1

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

• polymerization needs properly prearranged monomers with intermolecular hydrogen bonding patterns fitting between molecules. In this sense the conformational freedom is a main limiting factor in molecular design. On the other hand in forms stabilized by an intramolecular hydrogen bond it is possible to break an

• to exist: a) breakage of the intramolecular hydrogen bond(s) and b) association of two (or more) molecules of 1a that are much less rigid structures than other ones locked by intramolecular HB. The probability of existence of form 1a is low at lowered temperatures. The signal broadening at room

• intramolecular hydrogen bond we opt for argument "a". Figure 9 shows the changes in the spectra upon cooling (top spectrum represents +20 °C, spectra were recorded in 5° steps; the last spectrum at bottom represents a temperature of −70 °C). The coalescence temperature for complex 1∙∙∙10 is −15 °C. At

An intramolecular C–N cross-coupling of β-enaminones: a simple and efficient way to precursors of some alkaloids of Galipea officinalis

• Hana Doušová,
• Radim Horák,
• Zdeňka Růžičková and
• Petr Šimůnek

Beilstein J. Org. Chem. 2015, 11, 884–892, doi:10.3762/bjoc.11.99

• ) indicates the presence of an intramolecular hydrogen bond N–H···O. The enaminones 3 therefore possess Z configuration on the C=C bond. The intramolecular C–N cross-coupling β-Enaminones and related polarized ethylenes (generally enamines substituted by EWG on β-carbon atom) belong among the rather neglected

• compounds 1 (δ > 12), it can be assumed that all of these compounds have Z configuration on the C=C double bond (increased chemical shifts due to the presence of an intramolecular hydrogen bond C=O···H–N). This assumption was confirmed by means of X-ray characterization of the compound 1a (Figure 4

Fluoride-driven ‘turn on’ ESPT in the binding with a novel benzimidazole-based sensor

• Kai Liu,
• Xiaojun Zhao,
• Qingxiang Liu,
• Jianzhong Huo,
• Bolin Zhu and
• Shihua Diao

Beilstein J. Org. Chem. 2015, 11, 563–567, doi:10.3762/bjoc.11.61

• studies, which were conducted in DMSO-d6. The characteristic peak of BIP at 12.85 ppm suggested the formation of an intramolecular hydrogen bond in BIP itself between the imine nitrogen and the phenolic OH proton [32][33][34], that progressively disappeared with the successive addition of F− (see Figure

• ][33][34], suggested the formation of the geometrically restricted six-membered intramolecular hydrogen bond ring in the BIP at transition state [32][33][34]. As displayed in Figure 3, with gradual addition of F− to the CH3CN solution of BIP, the fluorescence intensity at 411 nm increased slowly. This

The preparation of new functionalized [2.2]paracyclophane derivatives with N-containing functional groups

• Henning Hopf,
• Swaminathan Vijay Narayanan and
• Peter G. Jones

Beilstein J. Org. Chem. 2015, 11, 437–445, doi:10.3762/bjoc.11.50

• ): The molecule of compound 18 in the crystal; ellipsoids represent 50% probability levels. The intramolecular hydrogen bond is indicated by a dashed line. (b, below): Packing diagram of 18 viewed parallel to the c axis in the region z ≈ 0. Intermolecular hydrogen bonds (one classical, one "weak") are