Showing papers on "Substituent published in 2002"

Organic electroluminescent element and display device

Abstract: PROBLEM TO BE SOLVED: To provide an organic electroluminescent element of excellent luminous efficiency with a long service life, and a display device of low power consumption with a long service life using the organic electroluminescent element. SOLUTION: This organic electroluminescent element with an organic layer clamped between two electrodes contains a compound expressed by a general formula (1), in at least one layer of the organic layer. In the formula, B represents a boron atom, C represents a carbon atom, A11 , A12 and A13 represent a carbon atom or a nitrogen atom, Z11 , Z12 and Z13 represent an atomic group required to complete an aromatic ring, R11 , R12 and R13 independently represent an alkyl group, an alkyloxy group, an aryloxy group or an halogen atom, R14 , R15 and R16 independently represent a hydrogen atom or a monovalent substituent, and l, m, n independently represent 0-7.

Collagen stability: insights from NMR spectroscopic and hybrid density functional computational investigations of the effect of electronegative substituents on prolyl ring conformations

Abstract: Collagen-like peptides of the type (Pro-Pro-Gly)10 fold into stable triple helices. An electron-withdrawing substituent at the Hγ3 ring position of the second proline residue stabilizes these triple helices. The aim of this study was to reveal the structural and energetic origins of this effect. The approach was to obtain experimental NMR data on model systems and to use these results to validate computational chemical analyses of these systems. The most striking effects of an electron-withdrawing substituent are on the ring pucker of the substituted proline (Proi) and on the trans/cis ratio of the Xaai-1−Proi peptide bond. NMR experiments demonstrated that N-acetylproline methyl ester (AcProOMe) exists in both the Cγ-endo and Cγ-exo conformations (with the endo conformation slightly preferred), N-acetyl-4(R)-fluoroproline methyl ester (Ac-4R-FlpOMe) exists almost exclusively in the Cγ-exo conformation, and N-acetyl-4(S)-fluoroproline methyl ester (Ac-4S-FlpOMe) exists almost exclusively in the Cγ-endo co...

Second Generation Light-Driven Molecular Motors. Unidirectional Rotation Controlled by a Single Stereogenic Center with Near-Perfect Photoequilibria and Acceleration of the Speed of Rotation by Structural Modification

Abstract: Nine new molecular motors, consisting of a 2,3-dihydro-2-methylnaphtho[2,1-b]thiopyran or 2,3-dihydro-3-methylphenanthrene upper part and a (thio)xanthene, 10,10-dimethylanthracene, or dibenzocycloheptene lower part, connected by a central double bond, were synthesized. A single stereogenic center, bearing a methyl substituent, is present in each of the motors. MOPAC93-AM1 calculations, NMR studies, and X-ray analysis revealed that these compounds have stable isomers with pseudoaxial orientation of the methyl substituent and less-stable isomers with pseudoequatorial orientation of the methyl substituent. The photochemical and thermal isomerization processes of the motors were studied by NMR and CD spectroscopy. The new molecular motors all show two cis-trans isomerizations upon irradiation, each followed by a thermal helix inversion, resulting in a 360 degrees rotation around the central double bond of the upper part with respect to the lower part. The direction of rotation is controlled by a single stereogenic center created by the methyl substituent at the upper part. The speed of rotation, governed by the two thermal steps, was adjusted to a great extent by structural modifications, with half-lives for the thermal isomerization steps ranging from t(1/2)(theta) 233-0.67 h. The photochemical conversions of two new motors proceeded with near-perfect photoequilibria of 1:99.

Electrochemical, Conductive, and Magnetic Properties of 2,7-Carbazole-Based Conjugated Polymers

Abstract: Novel poly(2,7-carbazole)s (i.e., poly(N-octyl-2,7-carbazolediyl) and poly(N-(4-hexylbenzoyl)-2,7-carbazolediyl)) and their alternating thiophene, bithiophene, and 3,4-ethylenedioxy-2,5-thienylene copolymers have been investigated by cyclic voltammetry, UV−vis spectroelectrochemistry, electrochemical quartz crystal microbalance, in-situ electron spin resonance, and in-situ conductivity techniques. All polymer films undergo reversible oxidation and partially reversible reduction processes. In poly(N-octyl-2,7-carbazolediyl), two isoelectronic oxidation processes produce radical cations and dications with charge localization at the carbazole subunits. The presence of a strong electron-withdrawing substituent onto the nitrogen atom in the homopolymer leads to an increase by 3 orders of magnitude of the conductivity (i.e., 1 × 10-2 S/cm). Similarly, in alternating copolymers, the oxidative charge is more delocalized over the polyconjugated backbone with in-situ conductivities in the range of 4 × 10-2−4 × 10-3...

The electronic influence of ring substituents and ansa bridges in zirconocene complexes as probed by infrared spectroscopic, electrochemical, and computational studies.

Abstract: The electronic influence of unbridged and ansa-bridged ring substituents on a zirconocene center has been studied by means of IR spectroscopic, electrochemical, and computational methods. With respect to IR spectroscopy, the average of the symmetric and asymmetric stretches (νCO(av)) of a large series of dicarbonyl complexes (CpR)2Zr(CO)2 has been used as a probe of the electronic influence of a cyclopentadienyl ring substituent. For unbridged substituents (Me, Et, Pri, But, SiMe3), νCO(av) on a per substituent basis correlates well with Hammett σmeta parameters, thereby indicating that the influence of these substituents is via a simple inductive effect. In contrast, the reduction potentials (E°) of the corresponding dichloride complexes (CpR)2ZrCl2 do not correlate well with Hammett σmeta parameters, thereby suggesting that factors other than the substituent inductive effect also influence E°. Ansa bridges with single-atom linkers, for example [Me2C] and [Me2Si], exert a net electron-withdrawing effect,...

Negative image-recording material and cyanine dye

Abstract: The invention provides a negative image-recording material for heat-mode exposure systems, which comprises (A) an IR absorbent including cyanine dye having a substituent that contains an atom having an atomic weight of at least 28 such as halogen atom, or a substituent that contains a non-covalent electron pair such as carbonyl group, (B) a radical generator and (C) a radically-polymerable compound, and which is imagewise exposed to IR rays for image formation thereon.

Novel spiropiperidines as highly potent and subtype selective σ-receptor ligands. Part 1

Abstract: A series of spiro[[2]benzopyran-1,4‘-piperidines] and spiro[[2]benzofuran-1,4‘-piperidines] of general structure 10 is prepared, and the affinity for σ1- and σ2-receptors is investigated by means of radioligand binding assays. The synthesis of the spiropiperidines 14a and 23 proceeds from bromine/lithium exchange of the bromoacetals 11 and 21, addition to piperidin-4-one 12a, and subsequent cyclization. Systematic variations of the substituent R at the nitrogen atom, the group X in position 3, and the ring size of the oxygen heterocycle are performed. The σ1- and σ2-receptor affinities are determined with guinea pig brain and rat liver membrane preparations using [3H]-labeled (+)-pentazocine and ditolylguanidine, respectively. Test results show that a benzyl residue at the piperidine nitrogen atom and a methoxy group in position 3 are advantageous for high σ1-receptor affinity. In this series the 1‘-benzyl-3-methoxy-3,4-dihydrospiro[[2]benzopyran-1,4‘-piperidine] (14a) and the 1‘-benzyl-3-methoxy-3H-spiro...

The O-H Bond Dissociation Energies of Substituted Phenols and Proton Affinities of Substituted Phenoxide Ions: A DFT Study

Abstract: The accurate O-H bond dissociation enthalpies for a series of meta and para substituted phenols (X-C 6 H 4 -OH, X=H, F, Cl, CH 3 , OCH 3 , OH, NH 2 , CF 3 , CN, and NO 2 ) have been calculated by using the (RO)B3LYP procedure with 6-311G(d,p) and 6-311++G(2df,2p) basis sets. The proton affinities of the corresponding phenoxide ions (X-C 6 H 4 -O - ) have also been computed at the same level of theory. The effect of change of substituent position on the energetics of substituted phenols has been analyzed. The correlations of Hammett’s substituent constants with the bond dissociation enthalpies of the O-H bonds of phenols and proton affinities of phenoxide ions have been explored. Keywords: Substituted Phenol, Bond Dissociation Energy, Acidity, DFT. I. Introduction Phenols are widely used as synthetic organic materials and also as antioxidants in living organisms [1]. Phenoxyl radicals are known as important intermediates in many biological and industrial applications [2]. Phenols are of special interest in organic chemistry, since their acid-base equilibria have often been used as reference values in establishing linear free energy relationships [3]. Consequently, much effort has been put to understand the factors governing the O-H bond dissociation energies, BDE(O-H), and acidities of substituted phenols, both in the solution and gas phase [4-11].

Determination of the Substituent Effect on the O−H Bond Dissociation Enthalpies of Phenolic Antioxidants by the EPR Radical Equilibration Technique

Abstract: The bond dissociation enthalpies (BDE) of several phenols containing electron-withdrawing substituents in the para position have been determined by means of the EPR radical equilibration technique. It has been found that CN, NO2, CHO, COOR, and COOH induce an increase of the BDE value of the O−H bond, thus producing a worsening of the antioxidant activity of phenols, while Cl, Ph, and CHCHPh show an opposite effect. The contributions of these substituents for the calculation of the BDE values in polysubstituted phenols by using the group additivity rule have also been derived. It is shown that this rule provides quite reliable predictions of bond strengths, so that the method can be conveniently used to estimate new data on substituted phenols.

Thieno[3,4-b]pyrazines: Synthesis, Structure, and Reactivity

Abstract: A general synthetic route has been developed for the efficient preparation of 2,3-disubstituted thieno[3,4-b]pyrazines These methods eliminate problems in the preparation of the precursor 3,4-diaminothiophene and utilize α-diones prepared through the reaction of the appropriate organocuprates with oxalyl chloride This combination allows the convenient preparation of thieno[3,4-b]pyrazine and its 2,3-disubstituted analogues (where substituent = methyl, hexyl, octyl, decyl, dodecyl, and phenyl) in high yield Characterization of the structure and reactivity of this class of compounds is also described, including the results of structural, electrochemical, and pKa studies

Deactivation Behavior and Excited-State Properties of (Coumarin-4-yl)methyl Derivatives. 2. Photocleavage of Selected (Coumarin-4-yl)methyl-Caged Adenosine Cyclic 3‘,5‘-Monophosphates with Fluorescence Enhancement

Abstract: A series of axial and equatorial diastereomers of (coumarin-4-yl)methyl-caged adenosine cyclic 3‘,5‘-monophosphates (cAMPs), 1−6, having methoxy, dialkylamino, or no substituent in the 6- and/or 7-positions, and their corresponding 4-(hydroxymethyl)coumarin photoproducts 7−12 have been synthesized. The photochemical and UV/vis spectroscopical properties (absorption and fluorescence) of 1−6 and 7−12 have been examined in methanol/aqueous HEPES buffer solution. Donor substitution in the 6-position causes a strong bathochromic shift of the long-wavelength absorption band, whereas substitution in the 7-position leads only to a weak red shift. The photochemical cleavage of the caged cAMPs was investigated, and the photoproducts were analyzed. Photochemical quantum yields, fluorescence quantum yields, and lifetimes of the excited singlet states were determined. The highest values of photochemical quantum yields (photo-SN1 mechanism) were obtained with caged cAMPs having a donor substituent in the 7-position of ...

Hexacoordinated ruthenium or osmium metal carbene metathesis catalysts

Abstract: The present invention relates to novel hexacoordinated metathesis catalysts and to methods for making and using the same. The inventive catalysts are of the formula wherein: M is ruthenium or osmium; X and X1 are the same or different and are each independently an anionic ligand; L, L1′ and L2 are the same or different and are each independently a neutral electron donor ligand, wherein at least one L, L1′ and L2 is an N-heterocyclic carbene ligand; and, R and R1 are each independently hydrogen or a substituent selected from the group consisting of C1-C20 alkyl, C2-C20 alkenyl, C2-C20 alkynyl, aryl, C1-C20 carboxylate, C1-C20 alkoxy, C2-C20 alkenyloxy, C2-C20 alkynyloxy, aryloxy, C2-C20 alkoxycarbonyl, C1-C20 alkylthio, C1-C20 alkylsulfonyl and C1-C20 alkylsulfinyl. Optionally, each of the R or R1 substituent group may be substituted with one or more moieties selected from the group consisting of C1-C10 alkyl, C1-C10 alkoxy, and aryl which in turn may each be further substituted with one or more groups selected from a halogen, a C1-C5 alkyl, C1-C5 alkoxy, and phenyl. Moreover, any of the catalyst ligands may further include one or more functional groups. Examples of suitable functional groups include but are not limited to: hydroxyl, thiol, thioether, ketone, aldehyde, ester, ether, amine, imine, amide, nitro, carboxylic acid, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate, and halogen.

Fluorescence enhancement of trans-4-aminostilbene by N-phenyl substitutions: the "amino conjugation effect".

Abstract: The synthesis, structure, and photochemical behavior of the trans isomers of 4-(N-phenylamino)stilbene (1c), 4-(N-methyl-N-phenylamino)stilbene (1d), 4-(N,N-diphenylamino)stilbene (1e), and 4-(N-(2,6-dimethylphenyl)amino)stilbene (1f) are reported and compared to that of 4-aminostilbene (1a) and 4-N,N-dimethylaminostilbene (1b). Results for the corresponding 3-styrylpyridine (2) and 2-styrylnaphthalene analogues (3) are also included. The introduction of N-phenyl substituents to 4-aminostilbenes leads to a more planar ground-state geometry about the nitrogen atom, a red shift of the absorption and fluorescence spectra, and a less distorted structure with a larger charge-transfer character for the fluorescent excited state. Consequently, the N-phenyl derivatives 1c-e have low photoisomerization quantum yields and high fluorescence quantum yields at room temperature, in contrast to the behavior of 1a, 1b, and most unconstrained monosubstituted trans-stilbenes. The isomerization of 1c and 1d is a singlet-state process, whereas it is a triplet-state process for 1e, presumably due to a relatively higher singlet-state torsional barrier. The excited-state behavior of 1f resembles 1a and 1b instead of 1c-e as a consequence of the less planar amine geometry and weaker orbital interactions between the N-phenyl and the aminostilbene groups. Such an N-phenyl substituent effect is also found for 2 and 3 and thus appears to be general for stilbenoid systems. The nature of this effect can be described as an "amino conjugation effect".

Red organic electroluminescent devices

Abstract: An organic EL device, having an anode and a cathode, and at least one organic luminescent medium including a compound of the formula: wherein: R1, and R2 are individually alkyl of from 1 to 20 carbon atoms, aryl, substituted aryl, carbocyclic and other heterocyclic systems; and R1, and R2 can be connected to form 5 or 6 member ring systems; and R3, and R4 are individually hydrogen; alkyl of from 1 to 10 carbon atoms, and a branched or unbranched 5 or 6 member substituent ring connecting with R1, R2 respectively; and R5 and R6 are individually hydrogen; alkyl of from 1 to 20 carbon atoms; aryl and heteroaryl of from 5 to 24 carbon atoms; and R6 can be connected with R5 to form a branched or unbranched 5 or 6 member carbocyclic ring.

Synthesis of a New Class of Chiral 1,5-Diphosphanylferrocene Ligands and Their Use in Enantioselective Hydrogenation

Abstract: A new family of ferrocenylphosphane ligands has been prepared. Their flexible synthesis allows many structural modifications. The asymmetric induction of these ligands was examined in the hydrogenation of functionalized C=C, C=O, and C=N bonds. The enantioselectivity of the reaction was strongly dependent on the substituent R at the position alpha to the ferrocene moiety. In many cases, both enantiomeric beta-hydroxyesters of the reduction product can be obtained by simply replacing a dimethylamino group in the ligand with a methyl group.

Combined Computational and Experimental Study of Substituent Effects on the Thermodynamics of H2, CO, Arene, and Alkane Addition to Iridium

Abstract: The thermodynamics of small-molecule (H2, arene, alkane, and CO) addition to pincer-ligated iridium complexes of several different configurations (three-coordinate d8, four-coordinate d8, and five-coordinate d6) have been investigated by computational and experimental means. The substituent para to the iridium (Y) has been varied in complexes containing the (Y-PCP)Ir unit (Y-PCP = η3-1,3,5-C6H2[CH2PR2]2Y; R = methyl for computations; R = tert-butyl for experiments); substituent effects have been studied for the addition of H2, C−H, and CO to the complexes (Y-PCP)Ir, (Y-PCP)Ir(CO), and (Y-PCP)Ir(H)2. Para substituents on arenes undergoing C−H bond addition to (PCP)Ir or to (PCP)Ir(CO) have also been varied computationally and experimentally. In general, increasing electron donation by the substituent Y in the 16-electron complexes, (Y-PCP)Ir(CO) or (Y-PCP)Ir(H)2, disfavors addition of H−H or C−H bonds, in contradiction to the idea of such additions being oxidative. Addition of CO to the same 16-electron co...

The formation of paracetamol (acetaminophen) adducts with hydrogen-bond acceptors

Abstract: The crystal structures of five hemiadducts of paracetamol with 1,4-dioxane, N-methylmorpholine, morpholine, N,N-dimethylpiperazine and piperazine and a related 1:1 adduct of paracetamol with 4,4′-bipyridine are described. All structures are characterized by the formation of chains of paracetamol molecules, which are linked via either OH⋯O=C interactions [C(9) chains in graph-set notation] or NH⋯O=C interactions [C(4) chains], depending on the presence or absence of substituent groups on the guest molecule. In all cases except for the morpholine and bipyridine adducts these chains are connected by hydrogen-bond interactions with the guest molecules, which reside on crystallographic inversion centres. In the bipyridine adduct this linkage also involves a π-stacking interaction; in the morpholine adduct it is formed between the OH groups of two opposed paracetamol molecules. Most adducts (that with 4,4′-bipyridine is an exception) decompose on heating to give monoclinic paracetamol. This is the first systematic study of a series of co-crystals containing paracetamol.

Additives for inhibiting gas hydrate formation

Abstract: The instant invention relates to the use of water-soluble polymers comprising structural elements of formula (I) wherein each R is independently H or C1-5-alkyl; X is H, an alkaline or earth alkaline metal or a quaternary ammonium group; R1 is H or C1-18-alkyl; and R2 is C1-18-alkyl; and wherein the alkyl groups represented by R1 and R2 may carry a hydroxy or amino substituent; and, if desired, a minor proportion of structural elements of formula (II) wherein R, R1, R2 and X may have the meaning as above, and Alk is a C1-C5-alkylene chain, as additives for inhibiting the formation of gas hydrates in connection with hydrocarbon production and transportation.

Polymeric fluorescent substance and polymer light-emitting device using the same

Abstract: Provided is a polymeric fluorescent substance comprising a copolymer which has a substituent containing a specific aromatic amine structure below in the side chain, wherein X1 is a divalent hydrocarbon group; Ar2 is an arylene group or the like; Ar3 and Ar4 independently represent an aryl group or the like. The polymeric fluorescent substance is preferably used for a light emitting layer of a polymer LED having high luminance and high light emitting efficiency.

The “Diindene” ArInInAr (Ar = C6H3-2,6-Dipp2, Dipp = C6H3-2,6-Pri2). Dimeric versus Monomeric In(I) Aryls: para-Substituent Effects in Terphenyl Ligands

Abstract: The synthesis and structure of a “diindene” with significant metal−metal bonding are described. It has an In−In distance of 2.9786(5) A, an In−In−C angle of 121.23(6)°, and an In−In bond order that is probably less than unity.

7-Substituted 5-amino-2-(2-furyl)pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidines as A2A adenosine receptor antagonists: a study on the importance of modifications at the side chain on the activity and solubility.

Abstract: It was demonstrated in the early 1990s that adenosine exerts many physiological functions through the interaction with four different receptors, named A1, A2A, A2B, and A3. In the past few years, our group has been involved in the development of A2A antagonists, which led to the synthesis of SCH 58261 (1), the first potent and selective adenosine A2A antagonist, which has been widely used as a reference compound. In this paper, we present an extended series of pyrazolotriazolopyrimidines synthesized with the aim to investigate the influence of the substitutions on the pyrazole ring. The choice of the substituents was based on their capability to improve water solubility while retaining high affinity and selectivity at the human A2A adenosine receptor subtype. In this series, some structural characteristics that are important for activity, i.e., tricyclic structure, free amino group at 5-position, furan ring, and substituent at 7-position on the pyrazole moiety, have been maintained. We focused our attenti...

Electron-withdrawing substituents decrease the electrophilicity of the carbonyl carbon. An investigation with the aid of (13)C NMR chemical shifts, nu(C[double bond]O) frequency values, charge densities, and isodesmic reactions to interpret substituent effects on reactivity.

Abstract: (13)C NMR chemical shifts and nu(C[double bond]O) frequencies have been measured for several series of phenyl- or acyl-substituted phenyl acetates and for acyl-substituted methyl acetates to investigate the substituent-induced changes in the electrophilic character of the carbonyl carbon. Charge density, bond order, and energy calculations have also been performed. The spectroscopic and charge density results indicate that opposite to the conventional thinking, electron-withdrawing substituents do not increase the electrophilicity of the carbonyl carbon but instead decrease it. On the other hand, reaction energies of the isodesmic reactions designed show that electron-withdrawing substituents destabilize the carbonyl derivatives investigated. So, a significant ground-state destabilization of carboxylic acid esters, and carbonyl compounds in general, due to the decreased resonance stabilization, is proposed as a novel concept to explain both the increase in their reactivity and the changes in the chemical shifts and carbonyl frequencies induced by electron-withdrawing substituents.

Density Functional Calculations of Electronic g-Tensors for Semiquinone Radical Anions. The Role of Hydrogen Bonding and Substituent Effects

Abstract: A recently developed density functional approach has been used to carry out a systematic computational study of electronic g-tensors for a series of 1,4-semiquinone radical anions. Good agreement with high-field EPR data in frozen 2-propanol is achieved only after taking into account the significant reduction of g-tensor anisotropy caused by hydrogen bonding to solvent molecules. The comparison of various model systems for the first solvation shell suggests two hydrogen bonds from 2-propanol molecules to each of the carbonyl groups of the radical anions, and one additional hydrogen bond to each of the methoxy groups in ubiquinone systems. 2-Propanol makes stronger hydrogen bonds than water and thus influences g-tensor anisotropy more strongly. Substituent effects at the semiquinone are reproduced quantitatively by the calculations. The g-tensor anisotropy is influenced significantly by the conformations of methyl and methoxy substituents, with opposite contributions. Analyses and interpretations of the interrelations between structure, bonding, and spectroscopic data are provided. The relevance of the computational results for the EPR spectroscopy of semiquinone radical anions in photosynthetic reaction centers is discussed.

A joint structural, kinetic, and thermodynamic investigation of substituent effects on host-guest complexation of bicyclic azoalkanes by β-cyclodextrin

Abstract: Derivatives of the azoalkane 2,3-diazabicyclo[2,2,2]oct-2-ene (1a) with bridgehead 1,4-dialkyl (1b), 1,4-dichloro (1c), 1-hydroxymethyl (1d), 1-aminomethyl (1e), and 1-ammoniummethyl (1f) substituents form host−guest inclusion complexes with β-cyclodextrin. They were employed as probes to assess substituent effects on the kinetics and thermodynamics of this complexation by using time-resolved and steady-state fluorimetry, UV spectrophotometry, induced circular dichroism (ICD) measurements, and 1H NMR spectroscopy. The kinetic analysis based on quenching of the long-lived fluorescence of the azoalkanes by addition of host provided excited-state association rate constants between 2.6 × 108 and 7.0 × 108 M-1 s-1. The binding constants for 1a (1100 M-1), 1b (900 M-1), 1c (1900 M-1), 1d (180 M-1), 1e (250 M-1), and 1f (ca. 20 M-1) were obtained by UV, NMR, and ICD titrations. A positive ICD signal of the azo absorption around 370 nm was observed for the β-cyclodextrin complexes of 1a, 1d, and 1f with the inten...

Probing the ATP Ribose-Binding Domain of Cyclin-Dependent Kinases 1 and 2 with O(6)-Substituted Guanine Derivatives

Abstract: O(6)-substituted guanines are adenosine 5'-triphosphate (ATP) competitive inhibitors of CDK1/cyclin B1 and CDK2/cyclin A, the O(6) substituent occupying the kinase ribose binding site. Fifty-eight O(6)-substituted guanines were prepared to probe the ribose pocket, and the structures of four representative compounds bound to monomeric CDK2 were determined by X-ray crystallography. Optimum binding occurs with a moderately sized aliphatic O(6) substituent that packs tightly against the hydrophobic patch presented by the glycine loop, centered on Val18, an interaction promoted by the conformational restraints imposed in a cyclohexylmethyl or cyclohexenylmethyl ring. Structure-based design generated (R)-(2-amino-9H-purin-6-yloxymethyl)pyrrolidin-2-one (56), which reproduces the reported hydrogen bonds formed between ATP and Asp86 and Gln131 but failed to improve inhibitory potency. Thus, the parent compound O(6)-cyclohexylmethylguanine (NU2058, 25) is the preferred starting point for exploring other areas of the kinase active site.

Syntheses, Structures and Properties of Kinetically Stabilized Distibenes and Dibismuthenes, Novel Doubly Bonded Systems between Heavier Group 15 Elements.

Abstract: The first stable distibene (RSb=SbR) and dibismuthene (RBi=BiR) were successfully synthesized by taking advantage of steric protection using an efficient steric protection group, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt). Since it is quite difficult to investigate the reactivities of the distibene (TbtSb=SbTbt) and dibismuthene (TbtBi=BiTbt) in solution due to their extremely low solubility values, similarly overcrowded distibene and dibismuthene, BbtE=EBbt (E = Sb, Bi), with sufficiently high solubility were also synthesized using another bulky substituent, 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl group (Bbt). The crystallographic analysis and spectroscopic studies of these stable dipnictenes led to the systematic comparison of structural parameters and physical properties for all homonuclear doubly bonded systems between heavier group 15 elements. In addition to these experimentally obtained results, theoretical calculations for these doubly bonded systems also rev...

Addition of hydrogen sulfide to juglone.

Abstract: Evidence of the addition of hydrogen sulfide to 5-hydroxy-1,4-naphthoquinone (juglone) in aqueous solution was obtained by nuclear magnetic resonance spectrometry (NMR), electron paramagnetic resonance spectrometry (EPR), UV-visible absorbance spectroscopy, and kinetic measurements. Although numerous addition reactions of thiolated alkane and aromatic compounds to quinones have been previously reported, this study indicates that inorganic forms of S(-II) act as nucleophiles and electrophiles in addition reactions to the alpha,beta-conjugated system of the quinone. The results obtained are consistent with competing Michael and radical addition reactions, with radical addition favored with increasing pH. The simplest structure that simulated the NMR spectrum was a sulfur molecule containing sulfur bonded between two juglone molecules at C-2 or C-3, while EPR measurements of aqueous reaction solutions indicated the presence of a stable semiquinone that contained a sulfur substituent at C-2 or C-3. Quinones are present in trace amounts in natural organic matter, and the addition of S(-II) has important implications with respect to transport and transformation of a variety of compounds that react with natural organic matter.