Neighboring Carbonyl Group Research Articles

Free radical formation from anthracycline antitumour: Agents and model systems—I model naphthoquinones and anthraquinones

Several naphthoquinones and anthraquinones were chosen as simple models of the anthracycline drugs and their semiquinone radical anions were generated by various methods. With the exception of 1,4-naphthoquinone, all of the quinones studied gave radicals that were highly reactive with oxygen, but which, in its absence, were stable over a limited pH range. The radicals were studied using electron spin resonance (ESR) spectroscopy and an examination was made of the effect on the distribution of the unpaired electron, of introducing various groups into the conjugated ring system. Hydroxyl groups capable of participating in strong intramolecular hydrogen bonding with neighbouring carbonyl groups had a marked influence on electron distribution and reduced the effects of intermolecular hydrogen bonding of the radicals with solvent molecules.

Die schwefelung c-substituierter maleinimide

C-Substituted maleimides 2, 4, 6 are thiated with the reagent 1 in toluene or xylene. Monothiation at the nonequivalent carbonyl groups occurs in a regiospecific way. Maleimides 2, 4 with 4-methylphenyl or dialkylamino groups are attacked on the carbonyl function which is far from the C-substituent and give the monothiocompounds 3 and 5. The thiation of maleimides 6a- 6b with NH-groups on the double bond primary occurs on the neighbouring carbonyl group in the neigh-bourhood. 7a and 7b further react to the violet dithiomaleimides 8. 6d gives the monothio compound 9 with an exocyclic CS-goups.

Anomalous exchange kinetics of peptide amide protons in aqueous solutions.

Reports concerning anomalous rates of exchange of some amides in oxytocin, alumichrome, and gramicidin S are reexamined through systematic analysis of the exchange data as a function of pH and primary structure. It is shown that such an analysis can provide useful information on secondary structure when the degree of hydrogen bonding to both the NH undergoing exchange and the neighboring carbonyl group are taken into consideration.

Neuartige Dicarbenstannylen-Komplexe und Stickstoff-Zinn-Ylid-Komplexe durch verwendung von [Sn(NMe 2) 2] 2 als komplexligand

The reaction of [Sn(NMe 2) 2] 2 with photochemically generated M(CO) 5 · THF complexes yields the dimeric nitrogen-tin ylide complexes [(CO) 5MSn(NMe 2) 2] 2 (M = Cr, Mo, W). With pentacarbonyliron by addition of the two SnN bonds to neighbouring carbonyl groups dicarbene-stannylene complexes are formed. The structures of these compounds are deduced from IR and 1H NMR spectra.

ChemInform Abstract: STRUCTURAL STUDIES IN METAL‐PURPURATE COMPLEXES. PART 1. CRYSTAL STRUCTURES OF POTASSIUM PURPURATE TRIHYDRATE AND AMMONIUM PURPURATE MONOHYDRATE (MUREXIDE)

The crystal structures of the title compounds, [K][L]·3H2O(1) and [NH4][L]·H2O(2)(L = purpurate, [C8H4N5O6]–) have been determined at 295 K by X-ray diffraction and refined by full-matrix least squares to R 0.059 (517 ‘observed’ reflections) and 0.080 (874 ‘observed’ reflections) respectively. Crystals of both are orthorhombic. For (1)(space group Ibca), a= 21.75(1), b= 16.512(3), c= 7.4304(7)A. Z= 8; for (2)(space group Pbnn), a= 4.5688(8), b= 15.309(5), c= 17.011 (4)A, Z= 4. In both structures, the anion has crystallographic symmetry 2, the angles at the central nitrogen being 126.3(7)(1) and 125.8(4)°(2). The two approximately planar barbiturate rings of each anion are not coplanar with each other, the interaction between neighbouring carbonyl groups causing torsion about the central nitrogen–carbon bonds. In both structures anion–cation interaction and hydrogen bonding is extensive.

The crystal structure of a tricarbonyliron-substituted cyclobutadiene complex: Tricarbonyl[1,2,2 a,12 a-η-5,10-dimethyldibenzo[ a,c]cyclobuta[ f]cyclooctene-3,12-dione] iron

The crystal structure of tricarbonyl[1,2,2 a,12 a-η-5,10-dimethyldibenzo[ a,c] cyclobuta[ f] cyclooctene-3,12-dione] iron, C 20O 2H 14Fe(CO) 3, has been determined by the single crystal X-ray diffraction technique using data collected with a fully automated diffractometer. The unit cell is monoclinic, space group P2 1/ c with a = 12.025(2), b = 23.204(3), c = 14.614(2) Å, β = 102.16(2)°, and contains eight molecules (two per asymmetric unit). The structure was elucidated to study the coordination of the iron atom and to correlate the conformation of the eight-membered ring with an NMR study. The final structure was obtained by Patterson-superposition and Fourier techniques and refined by full-matrix least-squares to a crystallographic residual of 0.070. In both independent molecules the iron atom is 1.77 Å from the cyclobutadiene ring to which it is coordinated. The eight-membered ring is flattened from a boat conformation and the six-membered rings are twisted from coplanarity by an angle of 74°. The twist is such that if one ring points above the eight-membered ring, the other ring will point below it with concomitant pointing in the opposite sense by neighboring carbonyl groups. Such a structure has conformational chirality. It is postulated that the stability of each enantiometer is due to the particularly high energy of the transition state through which each would pass to achieve inter-conversion.

Structural studies in metal–purpurate complexes. Part 1. Crystal structures of potassium purpurate trihydrate and ammonium purpurate monohydrate (murexide)

The crystal structures of the title compounds, [K][L]·3H2O(1) and [NH4][L]·H2O(2)(L = purpurate, [C8H4N5O6]–) have been determined at 295 K by X-ray diffraction and refined by full-matrix least squares to R 0.059 (517 ‘observed’ reflections) and 0.080 (874 ‘observed’ reflections) respectively. Crystals of both are orthorhombic. For (1)(space group Ibca), a= 21.75(1), b= 16.512(3), c= 7.4304(7)A. Z= 8; for (2)(space group Pbnn), a= 4.5688(8), b= 15.309(5), c= 17.011 (4)A, Z= 4. In both structures, the anion has crystallographic symmetry 2, the angles at the central nitrogen being 126.3(7)(1) and 125.8(4)°(2). The two approximately planar barbiturate rings of each anion are not coplanar with each other, the interaction between neighbouring carbonyl groups causing torsion about the central nitrogen–carbon bonds. In both structures anion–cation interaction and hydrogen bonding is extensive.

Generation and interception of isobenzofurans from 2-(α-bromoalkyl)benzophenones

2-(Bromomethyl)benzophenone, prepared by side-chain bromination of 2-methylbenzophenone, is converted into naphthalene derivatives [(2), (4), and (5)] by heating in tetrachloromethane with olefinic or acetylenic dienophiles. A mechanism is suggested in which 1-phenylisobenzofuran is generated by displacement of bromide by the neighbouring carbonyl group; the isobenzofuran then undergoes cycloaddition and the cycloadducts are aromatised by the hydrogen bromide present. Similar reactions are observed with 2-(2-bromoethyl)benzophenone, but in this case the primary Diels–Alder adducts (7) and (8) can be isolated. Similarly, (Z)-4-bromo-1,3-di-phenylbut-2-en-1-one (9) is converted into 2,4-diphenylfuran by heating in ethanol.

Sequential displacement of chloride in N-aryl-and N-aroyl-carbonimidoyl dichlorides

Hydrolysis of carbonimidoyl dichlorides (1) occurs via base catalysed and uncatalysed pathways in 1:4 dioxanwater at 25°. Hammett ρ values measured under basic (ρ+1.26) and neutral (ρ–2.30) conditions indicate that the former involves direct attack by hydroxide ion on the substrate while in the latter unimolecular C–Cl bond cleavage (to give an azocarbonium ion intermediate) occurs. The observed solvent and common ion effects support this. The products of hydrolysis are the corresponding amines except at High pH where the decarboxylation of N-arylcarbamates formed as intermediate is slow. The reaction of (1) with morphine is SN2 to give the N-inminomethylmorpholine (2; Y = morpholino)initially; however, the intermediate (2; Y = morpholino) undergoes further hydrolysis (by an SN1 mechanism) more rapidly than the initial bimolecular step in all the dioxanwater solvent mixtures studied. N-Aroyl dichlorides (9) undergo nucleophilic displacement ca. 103-fold more rapidly than (1) while the rate of the subsequent SN1 step is reduced ca. 106-fold due to the destabilization of azocarbonium ion formation by the neighbouring carbonyl group. In general then at high nucleophile concentration and in solvens of low dielectric constant the intermediates (14) may be isolated (Y = 2, NMe, or O). The dichloride (9) also shows a pH independent rate of hydrolysis at low pH but this is attributed to nucleophilic attack by solvent water, representing the first time that this has been observed in an imidoyl halide system.

Oxidation processes in relation to the induction of enzymes in Jerusalem artichoke tuber slices.

The effect of diethyldithiocarbamate (DIECA) and ethylenediamine tetraacetate (EDTA) on the wounding-dependent induction of phenol oxidase and peroxidase in Jerusalem artichoke tuber slices has been investigated. DIECA which is a good inhibitor of oxidase reactions inhibits the induction of enzymes. EDTA which does not affect these reactions prevents the induction only at a concentration of 5 μmoles/ml. At a concentration of 1 μmole/ml, however, which stimulates the rate of oxygen uptake by the slices, EDTA also stimulates the induction of enzymes.The induction of enzymes was enhanced when slices were cultured in the presence of compounds having two neighboring carbonyl groups (dehydroascorbate, pyruvate, and oxalate).The rate of both induction and oxygen uptake increased with increasing intensity of slicing.

Competition between neighbouring-group participation by carbonyl groups and carbon acids in ester hydrolyses

The alkaline hydrolyses of methyl 8-acyl- and 8-aroyl-1-naphthoates have been examined: intramolecular catalysis by the neighbouring carbonyl group occurs for the 8-formyl and 8-(3′- and 4′-substituted benzoyl)esters; whereas, the 8-acetyl, 8-propionyl, and 8-iso-butyryl esters display catalysis by the neighbouring carbon acid.

Basicity of ketones of the cyclopentadienyl-tricarbonylmetal series

1. The basicities of a series of ketones of the cyclopentadienyltricarbonylnietals (M=Mn or Re) in aqueous sulfuric acid have been measured. 2. The magnitudes of σ+ for the cyclopentadienyltricarbonylmanganese and cyclopentadienyltricarbonylrhenium residues have been calculated. With respect to their total electronic influence under the conditions of the protonization of the neighboring carbonyl group, they are approximately equal to one another and possess electron-donating properties stronger than those of a phenyl nucleus.

Fluorescence and protein structure: X. Reappraisal of solvent and structural effects

1. 1.|Quantum efficiencies of fiuorescence and emission maxima were measured in a number of solvents for tryptophanyl and tyrosyl peptides, as well as simpler derivatives of indole and phenol. Fluorescence was internally quenched by carbonyl groups but this occurred only when the molecule was solvated by a hydrogen-bonding solvent such as water or an alcohol. In non-polar organic solvents, quenching by the carbonyl group was lost and fluorescence rose to values of the parent indole and phenol compound. 2. 2.|Fluorescence quenching occurred with derivatives that contained unionized acid, amide, ester and peptide groups. These groups, when present on other solute molecules, did not quench; that is, external quenching of indole and phenol by amides, esters, etc., did not occur. An amino group alone had no effect on fluorescence, but in the free amino acids and peptides an α-amino group enhanced the quenching action of a neighboring carbonyl group. Fluorometric titrations showed that this enhancement of the carbonyl quenching was in the order α-NH 3 + > α-NH 2 > H. 3. 3.|The bearing that these observations may have on fluorescence of proteins was discussed. A preliminary classification scheme for exposed and buried tryptophanyl and tyrosyl residues was described and a range of values was selected for the fluorescence efficiency of each type of residue.

Neighboring Group Effects on Ester Hydrolysis. II. Neighboring Carbonyl Groups

Neighboring Group Effects on Ester Hydrolysis. II. Neighboring Carbonyl Groups