Imine Structure Research Articles

DNA interchain cross-links formed by acrolein and crotonaldehyde.

Acrolein and higher alpha,beta-unsaturated aldehydes are bifunctional genotoxins. The deoxyguanosine adduct of acrolein, 3-(2-deoxy-beta-d-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-8-hydroxypyrimido[1,2-a]purin-10(3H)-one (8-hydroxy-1,N(2)-propanodeoxyguanosine, 2a), is a major DNA adduct formed by acrolein. The potential for oligodeoxynucleotide duplexes containing 2a to form interchain cross-links was evaluated by HPLC, CZE, MALDI-TOF, and melting phenomena. Interchain cross-links represent one of the most serious types of damage in DNA since they are absolute blocks to replication. In oligodeoxynucleotides containing the sequence 5'-dC-2a, cross-linking occurred in a slow, reversible manner to the extent of approximately 50%. Enzymatic digestion to form 3-(2-deoxy-beta-d-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-8-(N(2)-2'-deoxyguanosinyl)pyrimido[1,2-a]purin-10(3H)one (5a) and reduction with NaCNBH(3) followed by enzymatic digestion to give 1,3-bis(2'-deoxyguanosin-N(2)-yl)propane (6a) established that cross-linking had occurred with the exocyclic amino group of deoxyguanosine. It is concluded that the cross-link is a mixture of imine and carbinolamine structures. With oligodeoxynucleotide duplexes containing the sequence 5'-2a-dC, cross-links were not detected by the techniques enumerated above. In addition, (15)N-(1)H HSQC and HSQC-filtered NOESY spectra carried out with a duplex having (15)N-labeling of the target amino group established unambiguously that a carbinolamine cross-link was not formed. The potential for interchain cross-link formation by the analogous crotonaldehyde adduct (2b) was evaluated in a 5'-dC-2b sequence. Cross-link formation was strongly dependent on the configuration of the methyl group at C6 of 2b. The 6R diastereomer of 2b formed a cross-link to the extent of 38%, whereas the 6S diastereomer cross-linked only 5%.

Oxidation activity and stability of homogeneous cobalt-sulphosalen catalyst: Studies with a phenolic and a non-phenolic lignin model compound in aqueous alkaline medium

Oxidation activity and stability of cobalt-Schiff base complex catalyst, Co-sulphosalen, were studied in aqueous alkaline medium. The 4-coordinated Co-sulphosalen was shown to be an active catalyst, with molecular oxygen increasing the initial oxidation rates of both a phenolic (guaiacol) and a non-phenolic (veratryl alcohol) lignin model compounds. Studies with a visible absorption spectrometer showed that 4-coordinated Co-sulphosalen forms a new complex with pyridine, which attaches as axial ligand. The activity of Co-sulphosalen complex was not increased, however, but instead was slightly decreased by the addition of pyridine. With a newly developed HPLC method, it was shown that Co-sulphosalen is not stable but decomposes as a function of time. The decomposition of the catalyst through hydrolysis of its imine structures was independent of the oxidation of the model compound. The decomposition rate of Co-sulphosalen increased with increasing pH and was higher in the absence of oxygen. The presence of pyridine had virtually no effect on the stability of the catalyst.

Amides are novel protein modifications formed by physiological sugars

The elucidation of structure and formation of AGEs is of major interest to understand related pathophysiologies, such as the late complications in diabetes, atherosclerosis and aging, and to develop pharmaceutical strategies for their prevention [1,2]. The discrepancy between extent of protein modification and of fluorescence has led to the notion that the major sugar-derived protein modifications cannot be explained by colored, UV and fluorescence active structures. Furthermore, evidence has shown that potential structures must be labile to acid and alkaline hydrolysis and cannot be stabilized by sodium borohydride reduction [3].Following this concept, N6-{2-[(5-amino-5-carboxypentyl)amino]-2-oxoethyl}lysine (GOLA) and N6-glycoloyllysine (GALA) were identified as novel amide protein modifications mediated by physiological reducing sugars [4]. Their identity was unequivocally confirmed by independent synthesis and coupled liquid chromatography/mass spectrometry. Model reactions with Nα-t-BOC-lysine revealed glyoxal and glycolaldehyde as immediate precursors with reaction pathways directly linked to Nε-carboxymethyllysine (CML) via glyoxal–imine structures. Based on a common intermediate, the ratio of the amide crosslink GOLA to the imidazolium crosslink GOLD was favored towards the amide at lower glyoxal levels in incubations conducted at constant lysine concentrations. GOLA and GALA formation from the Amadori product of glucose with lysine was directly dependent on oxidation. Presence of aminoguanidine almost completely suppressed GALA formation, whereas GOLA was only inhibited by 16%. As the latter effect was exactly in line with changes in CML synthesis, it can be reasoned that during Amadori product degradation, 84% of GOLA originates via direct oxidative fragmentation and 16% via glyoxal–imine intermediates. In contrast, the formation of GALA must be explained solely via glyoxal–imines. An efficient enzymatic hydrolysis and analytical method was developed for the detection of labile amide modifications in highly modified proteins and in vivo. In a first attempt, GOLA was quantified in brunescent lens protein at 66 pmol/mg protein. This suggested that amide modifications are of major physiological relevance in comparison to the already established AGEs pentosidine, GOLD and MOLD.

Vibrational assignment of 4-amino-3-penten-2-one

The infrared and Raman spectra of 4-amino-3-penten-2-one and its two deuterated analogous have been measured. Comparison between the spectra recorded with two techniques, density functional theory (DFT) calculations and the spectral behavior upon deuteration was used for assignment of the vibrational spectra of the titled compound. DFT suggests a relatively strong intramolecular bent hydrogen bond with N⋯O distance in the range of 2.64–2.67 Å, which is in agreement with the observed νNH at 3180 cm −1. Existence of an intermolecular hydrogen bond is also shown in both solid and solution phases. The spectroscopic data support the enamine structure for this compound rather than imine structure.

ChemInform Abstract: The Influence of Imine Structure, Catalyst Structure and Reaction Conditions on the Enantioselectivity of the Alkylation of Alanine Methyl Ester Imines Catalyzed by Cu(ch‐salen).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The influence of imine structure, catalyst structure and reaction conditions on the enantioselectivity of the alkylation of alanine methyl ester imines catalyzed by Cu(ch-salen)

Systematic variation of the substrate structure has shown that the most effective substrates for Cu(ch-salen)-catalyzed asymmetric enolate alkylation reactions carried out under phase-transfer conditions are the para-chlorophenyl imines of amino esters. The other reaction parameters (solvent and stirring speed) have also been optimized. The introduction of substituents onto the aryl rings of the salen ligand was found not to have a beneficial effect on the enantioselectivity of the reaction.

Synthesis of enantiomerically enriched amines by chiral ligand mediated addition of organolithium reagents to imines

The effect of the imine and ligand structure on the enantioselective addition of organolithiums to imines has been studied. Thus, (−)-sparteine-mediated additions of MeLi and/or n-BuLi to p-anisidine derived phenylimine 1a afforded the corresponding amines with modest e.e.s. The use of bulkier or more reactive imines (naphthyl or tosyl imines) resulted in loss of enantioselectivity. The best enantioinduction with this ligand was obtained with enolizable imines 8 and 10. When bis(oxazolidines) were used as chiral ligands, a strong influence of their structure in the enantioselectivity of the addition of MeLi and n-BuLi to phenylimine 1a was observed.

Diazomethane Derivatives Bearing Dialkylaluminium or DialkylgalliumSubstituents – The Isomeric Diazomethane and Nitrile Imine StructuresRealized by the Different Coordination Behavior of Aluminium and Gallium

Lithium trimethylsilyldiazomethanide Li(SiMe3)CN2 reacted with the dialkylaluminium or -gallium halides R2AlCl and R2GaBr [R = CH(SiMe3)2] by the elimination of lithium halide and the formation of the corresponding aluminium or gallium diazo compounds. As shown by a crystal structure determination, the gallium derivative 1 adopts the nitrile imine structure, in which the gallium atom is coordinated by the terminal nitrogen atom of the diazo group. The N–N–C–Si moiety is almost ideally linear with N–N and C–N bond lengths of 125.5 and 115.9 pm on average. In contrast, the diazomethane structure was formed with dialkylaluminium chloride, and the aluminium atom in 2 is attached to the carbon atom of diazomethane. The almost linear N–N–C group (174.1°) has N–N and N–C distances of 120.0 and 126.4 pm, respectively, inverse to that of the gallium derivative. The bonding situations can best be described by the resonance structures R–C≡N+–N−–GaR2 for 1 and R2Al–(R)C=N+=N− for 2. The nitrile imine isomer of the aluminium compound could be detected by NMR spectroscopy as a by-product. Both compounds gave dimers in the solid state, a Ga2N2 four-membered heterocycle was formed of 1, while an eight-membered Al2C2N4 heterocycle resulted with 2.

Diazomethane Derivatives Bearing Dialkylaluminium or DialkylgalliumSubstituents – The Isomeric Diazomethane and Nitrile Imine Structures Realized by the Different Coordination Behavior of Aluminium and Gallium

Lithium trimethylsilyldiazomethanide Li(SiMe3)CN2 reacted with the dialkylaluminium or -gallium halides R2AlCl and R2GaBr [R = CH(SiMe3)2] by the elimination of lithium halide and the formation of the corresponding aluminium or gallium diazo compounds. As shown by a crystal structure determination, the gallium derivative 1 adopts the nitrile imine structure, in which the gallium atom is coordinated by the terminal nitrogen atom of the diazo group. The N–N–C–Si moiety is almost ideally linear with N–N and C–N bond lengths of 125.5 and 115.9 pm on average. In contrast, the diazomethane structure was formed with dialkylaluminium chloride, and the aluminium atom in 2 is attached to the carbon atom of diazomethane. The almost linear N–N–C group (174.1°) has N–N and N–C distances of 120.0 and 126.4 pm, respectively, inverse to that of the gallium derivative. The bonding situations can best be described by the resonance structures R–C≡N+–N−–GaR2 for 1 and R2Al–(R)C=N+=N− for 2. The nitrile imine isomer of the aluminium compound could be detected by NMR spectroscopy as a by-product. Both compounds gave dimers in the solid state, a Ga2N2 four-membered heterocycle was formed of 1, while an eight-membered Al2C2N4 heterocycle resulted with 2.

Synthesis of new adducts and co-ordination complexes of zirconium and titanium containing β-aminoketone ligands. Crystal structures of isostructural adducts MCl4·2PriHNCMeCHCMeO (M = Ti or Zr) and the complex [Zr(PhNCMeCHCMeO)2Cl2

The reaction of MCl4 (M = Zr or Ti) with β-aminoketones HL (R1HNCR2CHCR3O; R2 = R3 = Me; R2 = Me, R3 = CF3) yielded the bis(ligand) adducts MCl4·2HL (M = Zr, R1 = Pri or Ph; R2 = R3 = Me; or R1 = Pri, R2 = Me, R3 = CF3; M = Ti, R1 = Pri or CH2CHCH2, R2 = R3 = Me). Reaction of MCl4 with the alkali-metal salts of the β-aminoketone ligands yielded the bis(ligand) complexes [M(R1NCMeCHCMeO)2Cl2] (M = Zr, R1 = Ph, p-ClC6H4, p-MeOC6H4 or Pri; M = Ti, R1 = Ph or p-MeOC6H4). Crystal structure determinations of the isostructural compounds ZrCl4·2PriHNCMeCHCMeO and TiCl4·2PriHNCMeCHCMeO indicated an octahedral co-ordination environment around the metal with the trans monodentate N–O ligands bound through the oxygen only. Strong intramolecular hydrogen bonding of the hydrogen on the nitrogen with the ligand oxygen is consistent with a ligand immonium enolate structure. An X-ray study of the octahedral complex [Zr(PhNCMeCHCMeO)2Cl2] indicated that the oxygens of the chelating N–O ligands are trans to each other and the chloride ligands are in a cis arrangement. The plane of one N–O chelate is in the equatorial plane of the complex and the plane of the second N–O ligand is at right angles to the first. The ligand forms a predominantly delocalised chelate ring but some ene–imine structure is apparent.

Structural analysis of photo-oxidized (ethylenediamine)bis(2,2′-bipyridine)ruthenium(II) complexes by using on-line electrospray mass spectrometry of labeled compounds

Photo-oxidation of Ru(bpy)2(en)2+, where bpy = 2,2′-bipyridine, en = ethylenediamine, was studied in isotopic labeling experiments by using on-line electrospray mass spectrometry (ESMS). The complex was known to undergo photochemical dehydrogenation of a fourelectron oxidation, giving the α,α′-diimine complexes in a stepwise manner via a two-electron-oxidized intermediate that represents loss of two hydrogen atoms from the en ligand. On-line mass analysis after photoirradiation (λ > 420 nm) of Ru(bpy)2(ed)2+ (ed = ethylene-d4diamine) showed that the ligand of the intermediate with loss of two hydrogen atoms was not an enamine but had an imine structure. Also, a ligand-oxygenated complex that has mass 14 amu higher than the Ru(bpy)2(en)2+ complex was observed in the ES mass spectra. The ligand of this complex was proposed to have a nitroso structure as a primary product in 18O2 experiments. The oxygenated complex was not generated in a stepwise manner via the imine intermediate, but directly by loss of two amino hydrogen atoms and addition of an oxygen atom. The source of the oxygen atom would be from oxygen dissolved in solution rather than from water in solution. Another oxygenated complex Ru(bpy)2(NO 2 #x2212; )+ was produced by irradiation and the structure was identified in 18O2 experiments.

Electro‐optic applications of soluble polypyrrole

AbstractThe optical transmittance of the film spin‐cast from the polypyrrole(PPy) solution in chloroform depended on the thickness of the film. The film with 80% transmittance showed a surface resistivity of 23kΩ/□. A TN‐LCD cell with rubbed PPy films as the LC alignment layers responded properly to an applied potential of 3.0V. Reflective mode cholesteric LCD cells made with black PPy film electrodes responded to AC fields to switch between the planar and focal conic states. PPy with imine structures introduced by deprotonation of doped PPy with NaOH solution was used as a diode material to exhibit a photo‐current on exposing to light.

Semiempirical calculations of the hydrolysis of penicillin G

A theoretical study of the gas-phase alkaline hydrolysis of penicillin G on the assumption of a B AC2 mechanism is reported. Various semiempirical methods were used to determine the influence of different parameterizations on the process. Among the most salient results obtained, the standard AM1 method predicted opening of the thiazolidine ring to yield the corresponding imine and enamine structures.

Biomimetic Reductive Amination of Fluoro Aldehydes and Ketones via [1,3]-Proton Shift Reaction.(1) Scope and Limitations.

A systematic study of azomethine-azomethine isomerizations of the N-benzylimines 2, derived from fluorinated aldehydes or ketones and benzylamine, has been made. The results reveal that, in sharp contrast to hydrocarbon analogs, fluorinated imines of 2 in triethylamine solution undergo isomerizations to give the corresponding N-benzylidene derivatives 5 (for 5/2 K > 32) in good isolated yields. The rates of the isomerizations depend on the starting imine structures and increase in the following order: aryl perfluoroalkyl ketimine 2m, per(poly)fluoroalkyl aldimine 2a,d-g, perfluoroaryl aldimine 2h, alkyl perfluoroalkyl ketimine 2i,j. The presence of chlorine or bromine atoms in the alpha-position to the C=N double bond of the starting imine favors a dehydrohalogenation reaction, giving rise to unsaturated products 6-9. The azomethine-azomethine isomerization was studied and proven to proceed essentially (>98%) intramolecularly with isotope exchange experiments. High chemical yields, the simplicity of the experimental procedure, and the low cost of all reagents employed make this biomimetic transamination of fluorocarbonyl compounds a practical method for preparing fluorine-containing amines of biological interest.

Cure kinetics of a flexible aromatic dicyanate with schiff base structure

AbstractPolycyclotrimerization of a flexible aromatic dicyanate with a Schiff base structure was studied by means of differential scanning calorimetry (DSC). The study on dynamic DSC evaluated an apparent activation energy (Ea) of 75.8 kJ/mol and autocatalytic first‐order kinetics with rate expression Af(α) = 1.96 X 105 (1 + 4.39 α) (1 ‐ α) min−1. The kinetic feature can be explained by a proposed mechanism consisting of hydroxyl‐catalyzed and autocatalytic paths. The lower value of Ea compared with other aromatic dicyanates is due to the electron‐withdrawing linkage of the inherent imine (—CHN) structure. The kinetic feature is affected by the content of the residual impurities (e.g., phenols or absorbed water) in the corresponding sample. © 1995 John Wiley & Sons, Inc.

Stability of reduced polypyrrole

Electrochemically polymerized polypyrrole(PPy) shows changes in visible light spectrum during electrochemical reduction revealing changes in electron states of the conjugated double bond. The concentration of polarons increases fast in the early stage during reduction on expense of bipolarons but drops off momentarily to show an increase of bipolaron concentration which again decreases with further reduction. The reduced PPy is unstable to show changes in the visible light spectrum in less than one minute after cutting off applied potential. The absorption peak at 420nm assigned as π-π ∗ transition in the conjugated double bond shrinks fast to show a strong absorption around 800nm assigned as bipolaron. It is observed that the spectral changes slow down when hydroquinone is added to the system. The addition of hydroquinone in the system stabilized polaron not to couple with each other during natural oxidation of PPy and makes the polymer segments not to turn easily into a bipolaron state from a polaron state. Hydroquinone is oxidized in an aqueous system to produce protons which seem to stabilize free radicals in the polaron state. It is suggested that deprotonation of −N +H in the pyrrole ring develops into productions of an imine structure to loose the electrochemical reactivity.

ChemInform Abstract: Synthesis of β‐Lactams by Condensation of Titanium Enolates of 2‐ Pyridylthioesters with Imines. Influence of the Imine Structure on the trans/cis Stereoselectivity.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis of β-lactams by condensation of titanium enolates of 2-pyridylthioesters with imines. Influence of the imine structure on the trans/cis stereoselectivity

The condensation of the titanium enolates of C-2 alkyl substituted 2-pyridylthioesters with imines affords β-lactams in trans/cis ratios that largely depend on the structure of the C-imine residue. Bulky and non-chelating heteroatom-containing groups lead to the formation of trans β-lactams, while sterically non-requiring or chelating groups favour the formation of the cis-products. On the basis of NMR evidences a rationale is proposed to account for the observed stereoselectivity.

Ab initio and molecular mechanics calculations on imine derivatives: A study of the rotational barriers and the development of MM2 parameters

AbstractThe application of molecular mechanics methods for the study of structures has become a standard approach to conformational analysis. The MM2 force field has been extended to include imines. In general, a diverse group of aliphatic and aromatic imine structures can now be treated. The rotational energy profiles and barriers to N‐substituted imines about the Csp2Csp2 single bonds adjacent to CN functional group were calculated via ab initio MO theory. Information obtained from the quantum mechanical calculations at the 3‐21G, 6‐31G*, and MP4/6‐31G* //6‐31G* levels was used both to study the phenomena involved and to parameterize MM2. The syn‐anti isomerization was also studied, and the mechanistic pathways have been evaluated. In cases where the comparison with experimental data can be made, the agreements are good.

Structural dependence of polyanilines on reaction medium

The structures of the complexes obtained from the chemical oxidation of leucoemeraldine by Cu(ClO 4) 2·6H 2O and from the simultaneous polymerization and oxidation of aniline by Cu(ClO 4) 2·6H 2O in various solvents were studied using X-ray photoelectron spectroscopy (XPS) and infrared (IR) absorption spectroscopy. When acetonitrile was used as the reaction medium, the structures of the complexes obtained by the two different methods appeared similar, with a nitrogenonium ion structure analogous to that in emeraldine-hydrochloride. No significant imine structures were formed. In contrast, oxidation of some of the amine units of leucoemeraldine to the imine structure by Cu(ClO 4) 2·6H 2O could occur with tetrahydrofuran, methanol and H 2O. The complexes formed from the simultaneous polymerization and oxidation of aniline in protic solvents were electrically non-conducting and structurally different from that synthesized in acetonitrile. A partial loss of ClO 4 − anions also occurred when leucoemeraldine-perchlorate complexes were exposed to protic solvents.