Showing papers on "Substituent published in 1980"

Nucleoside conformation is determined by the electronegativity of the sugar substituent

Abstract: The proton and 13C NMR spectra of uridine, deoxyuridine and four 2' substituted uridines (dUn, dUz, dUcl and dUfl) are reported. A linear relationship between the electronegativity of the 2'-substituent and the carbon-13 chemical shift of C2' is observed. Taking into account the effect of electronegativity by using the correction proposed by Karplus or by Jankowski, the proton-proton coupling constants have been used to compute the conformational equilibria of the six uridines. It is shown that the contribution of the N form (3'-endo -2'-exo) increases with the electronegativity of the 2' substituent. Thus dUfl contains some 85% N form in solution. - Applying similar corrections to published data in the adenosine series, a similar correlation is observed. This observation, that the most polar substituent pulls the pucker to its side, holds also for 3'-substituted compounds, like cordycepin (3'dAdo) and 3'-deoxy-3'-amino-adenosine. It is suggested that the influence of the electronegativity could be the dominating effect of nucleoside conformations and would also hold for arabinosides and xylosides. This effect should therefore also be the principal force which determines the differences between DNA and RNA.

Photopolymerizable compositions featuring novel co-initiators

Abstract: A photopolymerizable composition, element and method of photopolymerizing the composition or element are disclosed wherein the composition comprises an addition polymerizable compound containing ethylenic unsaturation and a co-initiator including a photopolymerization activator and a photosensitizer. In one aspect of the invention, the photosensitizer is selected to be a coumarin having an absorption maximum between about 250 and about 550 nm, and a ##STR1## substituent in the 3-position wherein R1 is alkyl or alkenyl having 1-12 carbon atoms, or a carbocyclic or heterocyclic group having 5-20 nuclear carbon and hetero atoms, the coumarin and the activator being present in an amount sufficient to provide, when the composition is coated, dried and exposed to a medium-pressure mercury light source, a speed which is at least about one-fifth that of the same composition coated, dried and exposed identically except with a co-initiator consisting of Michler's ketone and benzophenone. In another aspect of the invention, the activator is selected to have the structure: ##STR2## wherein: J is -O-, -S- or a carbon-to-carbon bond; J1, J2, and J3 are each independently hydrogen; alkyl, alkoxy, or alkylthio having from 1 to 5 carbon atoms; aryloxy having from 6 to 10 carbon atoms; halogen; or any two of J1, J2, and J3 taken together comprise the atoms necessary to complete a 5- or 6-membered fused heterocyclic or aromatic ring; and Z is the number of atoms necessary to complete a heterocyclic or aromatic ring of from 4 to 6 ring atoms.

Effect of the acyl substituent on the equilibrium constant for hydration of esters

Abstract: Heats of hydrolysis have been measured for the trimethyl orthoesters of isobutyric, propionic, benzoic, methoxyacetic, chloroacetic, and cyanoacetic acids using aqueous acid with an organic cosolve...

Carbon‐13 NMR studies of nitrogen compounds. I—substituent effects of amino, acetamido, diacetamido, ammonium and trimethylammonium groups

Abstract: 13C NMR chemical shifts are reported for several alkyl or aryl amines, acetamides, diacetamides and ammonium and trimethylammonium salts. Substituent effects, determined with respect to chemical shifts of amino derivatives, are rationalized in terms of γ effects, steric interactions and for benzene derivatives, in terms of competition between inductive (σ1) and resonance (σR) effects. These perturbations can be used to assign chemical shifts of complex structures and to study certain chemical processes.

Structure-activity relationship of diphenylthiourea antivirals.

Abstract: The dependence between chemical structure and antiviral activity of N,N'-diphenylthioureas is studied by synthesis and testing of model compounds and use of conformational data. The analysis revealed a number of structural features as essential for the antiviral effect: (1) the presence of an intact -NHC(==S)NH- grouping; (2) the presence of a substituent of the XH type (X = O, NH) in the aromatic ring; (3) the distance between these substituents and the sulfur atom in the 6.68-6.75 A range for the active compounds: (4) a trans conformation of the -C(==S)NH-group bound to the substituted phenyl ring. The directed synthesis of compounds satisfying the above requirements yielded the derivative N-phenyl-N'-(m-aminophenyl)thiourea exhibiting a very high antipicornavirus activity in vitro and several other active analogues (four out of seven synthesized). The possible mechanism of interaction between the active diphenylthiourea derivatives and the viral target is discussed.

Conformational analysis of sterols: comparison of X-ray crystallographic observations with data from other sources.

Abstract: Cystallographic data on over 400 steroids collected in the Atlas of Steroid Structure provide information concerning preferred conformations, relative stabilities and substituent influence of the interactive potential of steroid hormones. Analysis of these data indicates that observed conformational details are intramolecularly controlled and that the influence of crystal packing forces is negligible. Crystallographic data on the orientation of the progesterone side chain contradict published force-field calculations. In 84 of 88 structures having a 20-one substituent, the C(16)-C(17)-C(20)-O(20) torsion angle is between 0 degrees and -46 degrees. The 4 torsion angles that lie outside this range do so because of a 16 beta-substituent and not because of crystal packing forces. Not one of the 88 structures is found to have a conformation in which the C(16)-C(17)-C(20)-O(20) torsion angle is within +/- 15 degrees of the most commonly calculated minimum energy value. The narrow range of side chain conformations seen in very different crystalline environments in the 88 crystal structure determinations and the predictable substituent influence apparent in the data strongly suggest that crystallographically observed conformers seldom deviate from minimum energy positions, regardless of hypothetical broad energy minima, metastable states and small barriers to rotation. The 96 crystallographically independent determinations of the cholestane 17-side chain show that the chain has 4 principal conformations (A:B:C:D), occurring in the ratio 69:8:8:11. Although the fully extended side chain is clearly the energetically most favored one, in 16 observations of cholesterol itself only 6 are in the extended conformation. Some of the correlated conformational changes in the chains can be rationalized on the basis of model studies, but others apparently result from subtle intramolecular forces. The unsaturated B ring provides another element of flexibility in the structure of cholesterol. The 5-ene B ring is normally observed in an 8 beta, 9 alpha-half-chair conformation. However, in structures containing more than one molecular in the crystallographic asymmetric unit, at least one of the 2 molecules is found to differ significantly from this form. It may be that this inherent flexibility is responsible for the presence of conformationally distnct molecules in the same crystal. The intermolecular interaction observed in the crystal structure of cholesterol and its fatty acid derivatives illustrate the type of interaction between the steroid ring system and hydrocarbon chains that can be expected in membrane bilayers.

A Reexamination of Inductive Substituent Constants Derived from pKa Values of 4-Substituted Quinuclidines. Polar effects. Part VIII

Abstract: pKa Values of 42 quinuclidinium perchlorates I have been measured in 0.1 M aqueous KCl-solution. In a few cases small corrections of earlier thermodynamic pKa values are indicated. These measurements, in conjunction with recent X-ray structure determinations, confirm the reliability of the inductive substituent constants σIq derived from them.

Structure--activity relationships in a series of novel 3,4-dihydro-4-oxopyrimido[4,5-b]quinoline-2-carboxylic acid antiallergy agents.

Abstract: A series of more than 50 new 3,4-dihydro-4-oxopyrimido[4,5-b]quinoline-2-carboxylic acid derivatives and related compounds with substituent variations at the 2, 3, and 5--9 positions was prepared and evaluated for antiallergy activity using the rat PCA assay. These compounds were obtained by the condensation of the appropriately substituted 2-aminoquinoline-3-carboxamides with dialkyl oxalates, followed by further chemical transformations. More than two-thirds of the compounds prepared exhibited intravenous activity ranging from 1 to 400 times disodium cromoglycate (DSCG). Structure--activity data suggest that the presence of a carboxylic acid moiety at the 2 position affords optimal potency and that esters are preferred for good oral absorption. Best oral activity, with ED50 values ranging from 0.3 to 3.0 mg/kg, was displayed by ethyl esters with methoxy and/or ethoxy groups at the 7 and 8 positions.

Chemical ionization mass spectra of mononitroarenes

Abstract: The H2 and CH4 chemical ionization mass spectra of a selection of substituted nitrobenzenes have been determined. It is shown that reduction of the nitro group to the amine is favoured by high source temperatures and the presence of water in the ion source. The H2 chemical ionization mass spectra are much more useful for distinguishing between isomeric compounds than the CH4 CI mass spectra because of the more extensive fragmentation. For ortho substituents bearing a labile hydrogen abundant [MH H2O]+ fragments are observed. When the substituent is electron-releasing both ortho and para substituted nitrobenzenes show abundant [MHOH]+ fragment ions while meta substituted compounds show abundant loss of NO and NO2 from [MH]+. The latter fragmentation is interpreted in terms of protonation para to the substituent or ortho to the vitro function, while the first two fragmentation routes arise from protonation at the nitro group. When the substituent is electron-attracting the chemical ionization mass spectra of isomers are very similar except for the H2O loss reaction for ortho compounds.

Comminuted inorganic materials

Abstract: According to the present invention a composition of matter is provided comprising the reaction product of a comminuted inorganic material and a substituted succinic anhydride having the formula: ##STR1## wherein at least one of R 1 , R 2 , R 3 and R 4 is a substituent selected from alkyl, alkenyl, alkynyl or aralkyl group having from 1 to about 30 carbon atoms or a substituted derivative thereof, and the remaining substituents are hydrogens. The substituent may be saturated or unsaturated, linear or branched, and may have from 1 to about 10 substitutions including halogen, tertiary amino, tertiary amide, ketal, episulfide, sulfonate, phosphonate, imide, carboxylate, carbonate, isocyanate, silane, epoxy, cyano, ether, thioether, carbonyl, aromatic nitro, or acetal. In a particular molecule, all of the R 1 , R 2 , R 3 and R 4 groups may be the same or different, so long as they fall within the above class.