Studies in chemical ionization mass spectrometry of some flavonoids

Formation of ions in chemical ionization mass spectrometry of flavonoid compounds has been studied. Production of adduct ions and fragment ions as a function of ring substituents and of reagent gas has been observed. Pressure and repeller field dependence of ions has been found as a function of ring substituents.     

Substituent cross-interaction effects on the electronic character of the C=N bridging group in substituted benzylidene anilines--models for molecular cores of mesogenic compounds. A 13C NMR study and comparison with theoretical results

13C NMR chemical shifts delta(C)(C=N) were measured in CDCl3 for a wide set of mesogenic molecule model compounds, viz. the substituted benzylidene anilines p-X-C6H4CH=NC6H4-p-Y (X = NO2, CN, CF3, F, Cl, H, Me, MeO, or NMe2; Y = NO2, CN, F, Cl, H, Me, MeO, or NMe2). The substituent dependence of delta(C)(C=N) was used as a tool to study electronic substituent effects on the azomethine unit. The benzylidene substituents X have a reverse effect on delta(C)(C=N): electron-withdrawing substituents cause shielding, while electron-donating ones behave oppositely, the inductive effects clearly predominating over the resonance effects. In contrast, the aniline substituents Y exert normal effects: electron-withdrawing substituents cause deshielding, while electron-donating ones cause shielding of the C=N carbon, the strengths of the inductive and resonance effects being closely similar. Additionally, the presence of a specific cross-interaction between X and Y could be verified. The electronic effects of the neighboring aromatic ring substituents systematically modify the sensitivity of the C=N group to the electronic effects of the benzylidene or aniline ring substituents. Electron-withdrawing substituents on the aniline ring decrease the sensitivity of delta(C)(C=N) to the substitution on the benzylidine ring, while electron-donating substituents have the opposite effect. In contrast, electron-withdrawing substituents on the benzylidene ring increase the sensitivity of delta(C)(C=N) to the substituent on the aniline ring, while electron-donating substituents act in the opposite way. These results can be rationalized in terms of the substituent-sensitive balance of the electron delocalization (mesomeric effects). The present NMR characteristics are discussed as regards the computational literature data. Valuable information has been obtained on the effects of the substituents on the molecular core of the mesogenic model compounds.     

Evaluation of flavonoids binding to DNA duplexes by electrospray ionization mass spectrometry

In this study, electrospray ionization mass spectrometry (ESI-MS) was used to investigate the binding interactions of ten flavonoid aglycones and ten flavonoid glycosides with DNA duplexes. Relative binding affinities of the flavonoids toward DNA duplexes were estimated based on the fraction of bound DNA. The results revealed that the 4'-OH group of flavonoid aglycones was essential for their DNA-binding properties. Flavonoid glycosides with sugar chain linked on ring A or ring B showed enhanced binding toward the duplexes over their aglycone counterparts, whereas glycosylation of the flavonol quercetin on ring C exhibited a less pronounced effect. The aglycone skeletons and other hydroxyl substitutions on the aglycone also have an effect on the fractions of bound DNA. Upon collision-induced dissociation, the complexes containing flavonoid aglycones underwent the predominant ejection of a neutral ligand molecule, suggesting an intercalative DNA-binding mode. However, for complexes containing flavonoid glycosides, the loss of nucleobase increased to different extents, indicating a stronger binding or different binding mode. The results may provide not only a deeper insight into the DNA-binding properties of flavonoids but also a useful guideline for the design of efficient DNA-binding agents for chemotherapy.     

Studies on ferrocene derivatives. Part XVI: steric effects on the ligand exchange reactions of alkylferrocenes

Ligand exchange reactions of alkylferrocenes with substituted benzenes were carried out. The steric effects of substituents on the reaction were almost equal irrespective of the site of the substituents, either on the cyclopentadienyl – or the benzene ring. For benzene ring substituents, the effect on the symmetrically substituted benzenes was greater than that on the unsymmetrically substituted benzenes.     

Study of the collision-induced radical cleavage of flavonoid glycosides using negative electrospray ionization tandem quadrupole mass spectrometry

Negative electrospray ionization tandem quadrupole mass spectrometry was used to study the collision-induced dissociation (CID) of the O-glycosidic bond from different commercially available flavonoid glycosides. Depending on the structure, flavonoid glycosides can undergo both a collision-induced homolytic and heterolytic cleavage of the O-glycosidic bond producing deprotonated radical aglycone ((Y(0) - H)(-*)) and aglycone (Y(0) (-)) product ions. The relative abundance of the radical aglycone to the aglycone fragment from flavonol-3-O-glycosides increased with increasing number of hydroxyl substituents in the B ring and in the order kaempferol - 相似文献   

13C NMR spectra of 9-methylcarbazoles and electron conductivity of the carbazole ring

The effect of substituents in the ring of 9-methylcarbazoles on the ¹³C NMR chemical shifts was determined. Correlation relationships between the inductive and resonance constants of the substituents and the chemical shifts were found. The transmission properties of the carbazole ring with respect to the electronic effects of substituents in the 3 position were evaluated on the basis of the results obtained. Nonadditivity of the effects of the substituents on the NMR chemical shifts within the limits of one phenyl ring of carbazole relative to monosubstituted benzenes was observed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 204–209, February, 1984.     

Acid-catalyzed reaction behavior of 1-silylcyclopropylmethanols

Treatment of 1-silylcyclopropylmethanols with TsOH in methanol gives different homoallyl ethers depending upon the configuration of substituents on cyclopropane ring and the kinds of substituents on carbinyl carbon. Especially, the reaction of cyclopropylmethanols having no substituents on the same side with silyl group on cyclopropane ring proceeds to give the corresponding E-homoallyl ethers with high stereoselectivity. The following protiodesilylation of resulting homoallyl ethers proceeds with retention of configuration.     

Substituents Effect on the Optical Properties of Benzonitrile and Oligobenzonitriles

During the past decades, the organic systems with good electronic and optical property,such as oligomer and polymers, have been attracted much attention because of theiroptical nonlinearity, fast response, relatively low cost, ease of fabrication and integrationinto devices. Generally to say, the common oligomers or polymers that we usually studyare all of carbon-carbon or heteroaromatic conjugated system. In previous work, thesynthesis of new linear -(C=N).- conjugated systems, polynitriles h…     

Main fragmentation routes of functionally substituted cyclopropenes under electron impact

The behaviour of substituted cyclopropenes under electron impact is to a large extent determined by the presence of the unsaturated three-membered ring which is capable of efficient delocalization of the positive charge. The loss of one of the substituents at the C(3) position of the small ring is characteristic for the fragmentation of cyclopropenes; the loss of the substituent which is less electron donating occurs preferentially. The presence of substituents with heteroatoms on the three-membered ring may lead to changes in the fragmentation scheme characteristic for the specific set of substituents.     

Origin of the relative stereoselectivity of the beta-lactam formation in the Staudinger reaction

The relative (cis, trans) stereoselectivity of the beta-lactam formation is one of the critical issues in the Staudinger reaction. Although many attempts have been made to explain and to predict the stereochemical outcomes, the origin of the stereoselectivity remains obscure. We are proposing a model that explains the relative stereoselectivity based on a kinetic analysis of the cis/trans ratios of reaction products. The results were derived from detailed Hammett analyses. Cyclic imines were employed to investigate the electronic effect of the ketene substituents, and it was found that the stereoselectivity could not be simply attributed to the torquoelectronic model. Based on our results, the origin of the relative stereoselectivity can be described as follows: (1) the stereoselectivity is generated as a result of the competition between the direct ring closure and the isomerization of the imine moiety in the zwitterionic intermediate; (2) the ring closure step is most likely an intramolecular nucleophilic addition of the enolate to the imine moiety, which is obviously affected by the electronic effect of the ketene and imine substituents; (3) electron-donating ketene substituents and electron-withdrawing imine substituents accelerate the direct ring closure, leading to a preference for cis-beta-lactam formation, while electron-withdrawing ketene substituents and electron-donating imine substituents slow the direct ring closure, leading to a preference for trans-beta-lactam formation; and (4) the electronic effect of the substituents on the isomerization is a minor factor in influencing the stereoselectivity.     

Synthesis and antitumor activity of benzimidazolyl-1,3,5-triazine and benzimidazolylpyrimidine derivatives

Triamino-substituted 1,3,5-triazine and pyrimidine derivatives were synthesized and tested for antitumor activities using some human cancer cell lines and murine leukemia cell lines. All the compounds having benzimidazolyl and morpholino groups as substituents on the 1,3,5-triazine ring showed antitumor activity. Pyrimidine derivatives having the same groups as substituents also showed antitumor activity. Among them, the compounds having 1-benzimidazolyl, morpholino and cis-2,3-dimethylmorpholino groups as substituents on the 1,3,5-triazine ring or pyrimidine ring exhibited the most potent antitumor activity, and these compounds exhibited no or very weak aromatase inhibitory activity. In contrast, the compounds having imidazolyl group instead of benzimidazolyl group as a substituent on the 1,3,5-triazine ring showed a potent aromatase inhibitory activity.     

Theoretical elucidation of structure-activity relationship of flavonoid antioxidants

AM1 method was employed to calculate flavonoid antioxidants, and the results obtained are as follows. Firstly, flavonoid hydroxyls at ortho position were more active than the hydroxyls at meta position in scavenging oxygen-free radicals, which resulted from the facts that (ⅰ) the former were stabilized by forming intramolecular hydrogen bond and (ⅱ) ortho benzoquinone formed in the former structures through resonance, which resulted in large percentage of distribution of spin density on ortho oxygen and low internal energy. Secondly, electron-attracting effect of ring C of chromone-flavonoids showed some passive effects on hydroxyls of ring A, making the OH less active. As ring C had little effect on ring B and hydroxyls of ring B in most flavonoids were at ortho position, the rule summarized from experiments showing that hydroxyls of ring B were more active in scavenging oxygen-free radicals was elucidated.     

Terminal end‐group efficiency for the nematic phase using model bicyclo[2.2.2]octanes

The synthesis is reported of new liquid crystals incorporating the 1,4‐disubstituted bicyclo[2.2.2]octane ring and a series of substituents in a terminal position on the molecular core. The nature of the terminal substituent is varied from apolar with a small dipole moment to polar with a strong dipole moment. The angle of the dipole moment with respect to the molecular axis is also varied. An updated order of terminal group efficiency for substituents in a terminal position for the nematic phase is provided. The bicyclo[2.2.2]octane ring shields halogen substituents in a lateral position on phenyl rings attached to the bicyclooctane ring to a small degree and reduces the steric efects of these substituents, giving rise to high relative nematic–isotropic transition temperatures.     

Terminal end-group efficiency for the nematic phase using model bicyclo[2.2.2]octanes

The synthesis is reported of new liquid crystals incorporating the 1,4-disubstituted bicyclo[2.2.2]octane ring and a series of substituents in a terminal position on the molecular core. The nature of the terminal substituent is varied from apolar with a small dipole moment to polar with a strong dipole moment. The angle of the dipole moment with respect to the molecular axis is also varied. An updated order of terminal group efficiency for substituents in a terminal position for the nematic phase is provided. The bicyclo[2.2.2]octane ring shields halogen substituents in a lateral position on phenyl rings attached to the bicyclooctane ring to a small degree and reduces the steric efects of these substituents, giving rise to high relative nematic-isotropic transition temperatures.     

Evidence of substituent-induced electronic interplay. Effect of the remote aromatic ring substituent of phenyl benzoates on the sensitivity of the carbonyl unit to electronic effects of phenyl or benzoyl ring substituents

Carbonyl carbon (13)C NMR chemical shifts delta(C)(C[double bond]O) measured in this work for a wide set of substituted phenyl benzoates p-Y-C(6)H(4)CO(2)C(6)H(4)-p-X (X = NO(2), CN, Cl, Br, H, Me, or MeO; Y = NO(2), Cl, H, Me, MeO, or NMe(2) ) have been used as a tool to study substituent effects on the carbonyl unit. The goal of the work was to study the cross-interaction between X and Y in that respect. Both the phenyl substituents X and the benzoyl substituents Y have a reverse effect on delta(C)(C[double bond]O). Electron-withdrawing substituents cause shielding while electron-donating ones have an opposite influence, with both inductive and resonance effects being significant. The presence of cross-interaction between X and Y could be clearly verified. Electronic effects of the remote aromatic ring substituents systematically modify the sensitivity of the C[double bond]O group to the electronic effects of the phenyl or benzoyl ring substituents. Electron-withdrawing substituents in one ring decrease the sensitivity of delta(C)(C[double bond]O) to the substitution of another ring, while electron-donating substituents inversely affect the sensitivity. It is suggested that the results can be explained by substituent-sensitive balance of the contributions of different resonance structures (electron delocalization, Scheme 1).     

Gold(I)-catalyzed ring expansion of cyclopropanols and cyclobutanols

The rearrangement of 1-alkynyl cyclobutanols and cyclopropanols to alkylidene cycloalkanones catalyzed by cationic triarylphosphine gold(I) complexes is described. The reaction tolerates terminal alkynes as well as alkyl, aryl, and halo-substitution at the acetylenic position and stereoselectively provides a single olefin isomer. The gold(I)-catalyzed rearrangement is stereospecific with regard to substituents on the ring, thus providing a practical method for the stereoselective synthesis of highly substituted cyclopentanones from cyclopropanols. The reaction stereoselectively provides a single olefin isomer and is stereospecific with regard to substituents on the ring via sequential gold(I)-catalyzed ring expansion reactions.     

Effect of substituents at atoms of double bonds on the conformation of the 1,3-cyclohexadiene ring

The effect of alkyl substituents at atoms of double bonds on the conformation of the 1,3-cyclohexadiene ring was studied using a molecular-mechanics method. It was shown that the introduction of substituents results only in a change of the degree of ring puckering. It is concluded that there is equilibrium between flattening and unflattening factors, which then governs the constancy of the ring conformation.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 4, pp. 334–337, July–August, 1992.     

1H NMR spectra and electronic structure of 3-arylmethyl-idenephthalide and 3-arylthiomethylidenephthalide derivatives

The ¹H NMR spectra of trans-3-phenylmethylidenephthalide and trans-3-phenylthiomethylidenephthalide derivatives were investigated. After applying a correction for the anisotropy of substituents and/or for changes of ring current in the substituted aromatic ring, linear correlations were obtained between the chemical shifts of protons of the substituted phenyl group and the methine group and s? constants of substituents. The influence of the bridge heteroatom on the transfer of electronic effects of substituents through the molecules under study is discussed.     

Electrophilic substitution in a number of N-exo-carbamoyl derivatives of sydnoneimines

Depending on the character of the substituents and the reaction conditions, the bromination of N-exo-carbamoyl derivatives of sydnoneimines may proceed in the heterocyclic ring and (or) in the phenyl ring of the exocyclic substituent. Nitration proceeds only in the phenyl rings of the substituents.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1198–1203, September, 1975.     

Substituent effects in the reduction of trifluoroacetophenones by a dihydronicotinamide

Triflurooacetophenone reduction rates (by a dihydronicotinamide) and hydration equilibria are identically affected by ring substituents. High yields of alcohol are obtained when electron donating substituents are absent from the ring.