The contribution of non-classical CHax⋯OC hydrogen bonds to the anomeric effect in fluoro and oxa-methoxycyclohexanes

2021 ◽  
Vol 23 (10) ◽  
pp. 5845-5851
Author(s):  
Bruno A. Piscelli ◽  
David O’Hagan ◽  
Rodrigo A. Cormanich
Keyword(s):  
Hydrogen Bonds ◽  
Anomeric Effect ◽  
Anomeric Effects

In this theory study the dominance of non-classical 1,3-diaxial CHax⋯OC hydrogen bonds (NCHBs) dictating anomeric effects in fluorinated methoxycyclohexanes and 2-methoxytetrahydropyrans is demonstrated, a phenomenon which is most often described as a consequence of hyperconjugation.

Anomeric effect for a 2,5,7-triazabicyclo[2.2.1]heptane derivative

2009 ◽  
Vol 65 (3) ◽  
pp. o115-o117 ◽  
Author(s):  
Amir Taheri ◽  
Sayed Mojtaba Moosavi
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Bond Length ◽  
Anomeric Effect ◽  
First Time ◽  
Anomeric Effects

A new member of the polyazapolycyclic family of compounds, namelyN3,N6,2,5,7-pentaphenyl-2,5,7-triazabicyclo[2.2.1]heptane-3,6-diamine xylene solvate, C34H31N5·C8H10, was synthesized for the first time and the crystal structure is reported. There are no hydrogen bonds joining the molecules. All four chiral C atoms have the same absolute configurations. With regard to the four N—C—N groups, anomeric effects are observed to cause a reduction of C—N bond length and N-atom pyramidality.

The syntheses of 6-C-alkyl derivatives of methyl α-isomaltoside for a study of the mechanism of hydrolysis by amyloglucosidase

2001 ◽  
Vol 79 (2) ◽  
pp. 238-255 ◽  
Author(s):  
Ulrike Spohr ◽  
Nghia Le ◽  
Chang-Chun Ling ◽  
Raymond U Lemieux
Keyword(s):  
Hydrogen Bonds ◽  
Molecular Model ◽  
Aromatic Amino Acids ◽  
Hydroxyl Group ◽  
Bulk Solution ◽  
Anomeric Effect ◽  
Nmr Studies ◽  
Intermolecular Hydrogen Bonds ◽  
Model Calculations ◽  
Derivatives Of

The epimeric (6aR)- and (6aS)-C-alkyl (methyl, ethyl and isopropyl) derivatives of methyl α-isomaltoside (1) were synthesized in order to examine the effects of introducing alkyl groups of increasing bulk on the rate of catalysis for the hydrolysis of the interunit α-glycosidic bond by the enzyme amyloglucosidase, EC 3.2.1.3, commonly termed glucoamylase (AMG). It was previously established that methyl (6aR)-C-methyl α-isomaltoside is hydrolysed about 2 times faster than methyl α-isomaltoside and about 8 times faster than its S-isomer. The kinetics for the hydrolyses of the ethyl and isopropyl analogs were also recently published. As was expected from molecular model calculations, all the R-epimers are good substrates. A rationale is presented for the catalysis based on conventional mechanistic theories that includes the assistance for the decomposition of the activated complex to products by the presence of a hydrogen bond, which connects the 4a-hydroxyl group to the tryptophane and arginine units. It is proposed that activation of the initially formed complex to the transition state is assisted by the energy released as a result of both of the displacement of perturbed water molecules of hydration at the surfaces of both the polyamphiphilic substrate and the combining site and the establishment of intermolecular hydrogen bonds, i.e., micro-thermodynamics. The dissipation of the heat to the bulk solution is impeded by a shell of aromatic amino acids that surround the combining site. Such shields are known to be located around the combining sites of lectins and carbohydrate specific antibodies and are considered necessary to prevent the disruption of the intermolecular hydrogen bonds, which are of key importance for the stability of the complex. These features together with the exquisite stereoelectronic dispositions of the reacting molecules within the combining site offer a rationalization for the catalysis at ambient temperatures and near neutral pH. The syntheses involved the addition of alkyl Grignard reagents to methyl 6-aldehydo-α-D-glucopyranoside. The addition favoured formation of the S-epimers by over 90%. Useful amounts of the active R-isomers were obtained by epimerization of the chiral centers using conventional methods. Glycosylation of the resulting alcohols under conditions for bromide-ion catalysis, provided methyl (6aS)- and (6aR)-C-alkyl-hepta-O-benzyl-α-isomaltosides. Catalytic hydrogenolysis of the benzyl groups afforded the desired disaccharides. 1H NMR studies established the absolute configurations and provided evidence for conformational preferences.Key words: amyloglucosidase (AMG), exo-anomeric effect, 6-C-alkyl-α-D-glucopyranosides and isomaltosides, mechanism of enzyme catalysis.

scholarly journals The origin of the generalized anomeric effect: possibility of CH/n and CH/π hydrogen bonds

2009 ◽  
Vol 344 (10) ◽  
pp. 1225-1229 ◽  
Author(s):  
Osamu Takahashi ◽  
Katsuyoshi Yamasaki ◽  
Yuji Kohno ◽  
Kazuyoshi Ueda ◽  
Hiroko Suezawa ◽  
...  
Keyword(s):  
Hydrogen Bonds ◽  
Anomeric Effect

scholarly journals Heteroatom Substitution at Amide Nitrogen—Resonance Reduction and HERON Reactions of Anomeric Amides

Molecules ◽  
2018 ◽  
Vol 23 (11) ◽  
pp. 2834 ◽  
Author(s):  
Stephen Glover ◽  
Adam Rosser
Keyword(s):  
Amide Bond ◽  
Anomeric Effect ◽  
Amide Nitrogen ◽  
Carbonyl Carbon ◽  
Heteroatom Substitution ◽  
Electronegative Atom ◽  
Anomeric Effects ◽  
Acyl Derivatives

This review describes how resonance in amides is greatly affected upon substitution at nitrogen by two electronegative atoms. Nitrogen becomes strongly pyramidal and resonance stabilisation, evaluated computationally, can be reduced to as little as 50% that of N,N-dimethylacetamide. However, this occurs without significant twisting about the amide bond, which is borne out both experimentally and theoretically. In certain configurations, reduced resonance and pronounced anomeric effects between heteroatom substituents are instrumental in driving the HERON (Heteroatom Rearrangement On Nitrogen) reaction, in which the more electronegative atom migrates from nitrogen to the carbonyl carbon in concert with heterolysis of the amide bond, to generate acyl derivatives and heteroatom-substituted nitrenes. In other cases the anomeric effect facilitates SN1 and SN2 reactivity at the amide nitrogen.

Configuration and conformation of alkoxyalkyl and hydroxyalkyl trifluoromethyl nitroxides. Anomeric effects and nitroxide conformations

1981 ◽  
Vol 59 (12) ◽  
pp. 1745-1752 ◽  
Author(s):  
C. Chatgilialoglu ◽  
K. U. Ingold
Keyword(s):  
Anomeric Effect ◽  
Conformational Preference ◽  
Nodal Plane ◽  
Spectral Parameters ◽  
Small Magnitude ◽  
Or Groups ◽  
Steric Factors ◽  
Hyperfine Splittings ◽  
Anomeric Effects ◽  
Configuration And Conformation

The epr spectral parameters for some [Formula: see text] radicals have been measured over a range of temperatures. These radicals are probably non-planar at nitrogen. Their OR groups are in the eclipsed position with respect to the N 2pz orbital, a conformational preference which is attributed to a combination of steric factors and the anomeric effect. For [Formula: see text] the H hyperfine splittings (hfs) are of unusually small magnitude. It is pointed out that all other known [Formula: see text] also have anomalously low H hfs. It is suggested that this is due to the anomeric effect which not only promotes the eclipsed conformation but also causes the OR group to bend towards the semioccupied orbital, thereby moving H and R2 towards the nodal plane of this orbital.

Ab initio modelling of the anomeric and exo anomeric effects in 2-methoxytetrahydropyran and 2-methoxythiane corrected for intramolecular BSSE

2015 ◽  
Vol 17 (28) ◽  
pp. 18501-18513 ◽  
Author(s):  
Vladimir Sladek ◽  
Filip Holka ◽  
Igor Tvaroška
Keyword(s):  
Ab Initio ◽  
Anomeric Effect ◽  
Oxygen Substitution ◽  
Anomeric Effects

Oxygen substitution in 2-methoxytetrahydropyran by sulphur in 2-methoxythiane approximately doubles the anomeric effect, which slows down enzymatic processing of 2-methoxythiane.

scholarly journals Crystal structure of the 1,3,6,8-tetraazatricyclo[4.3.1.13,8]undecane (TATU)–4-nitrophenol (1/2) adduct: the role of anomeric effect in the formation of a second hydrogen-bond interaction

2015 ◽  
Vol 71 (11) ◽  
pp. 1356-1360 ◽  
Author(s):  
Augusto Rivera ◽  
Héctor Jairo Osorio ◽  
Juan Manuel Uribe ◽  
Jaime Ríos-Motta ◽  
Michael Bolte
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Three Dimensional ◽  
Normal Donor ◽  
Anomeric Effect ◽  
Hydrogen Bond Interaction ◽  
Hydrogen Bond Formation ◽  
Dimensional Network ◽  
Crystalline Adduct ◽  
Donor Acceptor

In the title ternary co-crystalline adduct, C7H14N4·2C6H5NO3, molecules are linked by two intermolecular O—H...N hydrogen bonds, forming a tricomponent aggregates in the asymmetric unit. The hydrogen-bond formation to one of the N atoms is enough to induce structural stereoelectronic effects in the normal donor→acceptor direction. In the title adduct, the two independent nitrophenol molecules are essentially planar, with maximum deviations of 0.0157 (13) and 0.0039 (13) Å. The dihedral angles between the planes of the nitro group and the attached benzene rings are 4.04 (17) and 5.79 (17)°. In the crystal, aggregates are connected by C—H...O hydrogen bonds, forming a supramolecular dimer enclosing anR66(32) ring motif. Additional C—H...O intermolecular hydrogen-bonding interactions form a second supramolecular inversion dimer with anR22(10) motif. These units are linkedviaC—H...O and C—H...N hydrogen bonds, forming a three-dimensional network.

Synthesis and equilibration of conformationally rigid cis and trans tricyclic mono and dithioacetals. An evaluation of stereoelectronic (anomeric) effects in thioacetals

1985 ◽  
Vol 63 (10) ◽  
pp. 2757-2762 ◽  
Author(s):  
Pierre Deslongchamps ◽  
Daniel Guay
Keyword(s):  
Anomeric Effect ◽  
Cis And Trans ◽  
Anomeric Effects

The synthesis of cis and trans tricyclic monothioacetals 5–8 and dithioacetals 9 and 10 is reported (Schemes 1 and 2). The cis isomers 5, 7, and 9 are the kinetic products of cyclization, a result which is explained on the basis of stereoelectronic principles. Equilibration studies (Table 1) led to an evaluation of the anomeric effect for sulfur; it was found to be of the same order as that for oxygen.

scholarly journals Heteroatom Substitution at Amide Nitrogen — Resonance Reduction and HERON Reactions of Anomeric Amides

2018 ◽  
Author(s):  
Stephen A. Glover ◽  
Adam A. Rosser
Keyword(s):  
Amide Bond ◽  
Anomeric Effect ◽  
Amide Nitrogen ◽  
Carbonyl Carbon ◽  
Heteroatom Substitution ◽  
Electronegative Atom ◽  
Anomeric Effects ◽  
Acyl Derivatives

This review describes how resonance in amides is greatly affected upon substitution at nitrogen by two electronegative atoms.  Nitrogen becomes strongly pyramidal and resonance stabilisation, evaluated computationally, can be reduced to as little as 50% that of N,N-dimethylacetamide.  However, this occurs without significant twisting about the amide bond, which is borne out both experimentally and theoretically.  In certain configurations, reduced resonance and pronounced anomeric effects between heteroatom substituents are instrumental in driving the HERON (Heteroatom Rearrangement On Nitrogen)† reaction, in which the more electronegative atom migrates from nitrogen to the carbonyl carbon in concert with heterolysis of the amide bond, to generate acyl derivatives and heteroatom-substituted nitrenes.  In other cases the anomeric effect facilitates S­N1 and SN2 reactivity at the amide nitrogen.

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