Trifluoromethyl imidazoles

Some imidazole derivatives with trifluoromethyl substituents have been made, as part of a programme on the synthesis of fluorine-containing annyti-cancer agents. This work is a joint project between ourselves and Professor A.B. Foster's group at the Institute of Cancer Research, Royal Cancer Hospital, London. Imidazole carboxylic acids have been treated with sulphur tetrafluoride to give 2-trifluoromethyl-, 2,4-bis(trifluoromethyl)-, and 2,4,5-tris(trifluoromethyl)-imidazole. Some reactions of these trifluoromethyl derivatives have been studied. Ranges of N-substituted derivatives have been synthesised using the imidazole silver salts and the appropriate alkyl halide derivative. Hydrolytic stabilities of the CF₃ groups in the patent imidazoles have been studied.The 2-trifluoromethyl derivative is the least stable hydrolytically.     

Conformational analysis of 2', 3' and 4'-azachalcones by molecular orbital calculations

The semi-empirical quantum chemical PCILO method is used to perform a detailed conformational analysis of 2'-, 3'-and 4'-azachalcones. Several energy minima are obtained for each compound. Global energy minima (most stable conformations) are found for antiperiplanar-s-cis 2'-azachalcone, synperiplanar-s-cis 3'-azachalcone and s-cis 4'-azachalcone. The calculated results are compared with available experimental data.     

An analysis of the through-bond interaction using the localized molecular orbitals—IV: Long-range proton hyperfine coupling in exo- and endo-hydrogens in bicyclo[2.1.1]hex-5-yl radical

The INDO calculations were performed on bicyclo[2.1.1]hex-5-yl radical. From these calculations, it was confirmed that the hyperfine coupling constants depend largely on the geometry of the α hydrogen. The localized MO's were obtained from the canonical MO's calculated by using the INDO method. With the use of the localized MO's thus obtained, the variation in the hyperfine coupling constants at the 6exo- and 6endo-protons in this radical was explained in terms of the through-bond and/or the through-space interactions according to the procedure which we proposed previously. That is by the procedure we can selectively pick up a particular interaction between the specified localized MO's. The hyperfine coupling constant in this radical can be expressed by the summation of several interaction terms. The difference in the hyperfine spin coupling constants of the H_6exo and H_6endo in the radical now concerned has been attempted to explain using MO coefficients of the occupied orbitals.     

Determination of vanadium(V) with 3-(2-hydroxy-5-methylphenyl)-5-(p-methoxyphenyl)isoxazoline (HMPAO)

The extraction studies of vanadium(V) with 3-(2-hydroxy-5-methylphenyl)-5-(p-methoxyphenyl) isoxazoline (HMPAO) have been done. Vanadium is extracted into chloroform as a yellow-colored complex with HMPAO from 8.0 M HCl medium. The complex absorbs maximum at 400 nm. The system conforms to Beer's law over the concentration range 1.1–39 μg of vanadium per milliliter. The color of the complex was stable for 60 hr. Vanadium was extracted quantitatively and was determined in the presence of large number of foreign ions associated with it. The extractable species was 1:2 (V:HMPAO) in nature. The stability constants of the complex were determined by Yatsimirskii's and Leden's methods.     

Catalytic transfer hydrogenation of cyclodextrin azides and benzylated glucose derivatives

Debenzylation by catalytic transfer hydrogenation (CTH) of various organic compounds is a simple, fast, and safe method. Though CTH is widely used in reductions, only few data are available for the conversion of azides to amines. The number of usable transfer compounds is limited in cases of sugar derivatives, as the most common transfer materials, e.g. hydrazine hydrate or formic acid, can compete in side-reactions. The present study explores the limits of the reaction parameters and transfer compounds.A part of this publication was presented at EUROCARB VII, Cracow, Poland, 22–27 Aug. 1993.Dedicated to Professor József Szejtli.     

Nikolaĭ semenovich kurnakov,the reaction (1893) and the man (1860–1941) a ninety-year retrospective view

Kurnakov's classic thiourea reaction, proposed ninety years ago and still used to differentiate cis from trans isomers of dipositive platinum and palladium, represents his best known contribution to coordination chemistry. The circumstances surrounding its discovery, its implications, and its relationship to Peyrone's and Jørgensen's reactions and Chernyaev's trans effect are discussed. A brief discussion of Kurnakov's other studies of coordination compounds, and a short biography are also provided.     

Synthese de la cyclo-5'-8 desoxy-5' adenosine: stereochimie et mecanisme de la cyclisation d'un derive de l'iodo-5' adenosine par le zinc

N,N'-Dibenzoyl 2', 3'-O-isopropylidene 5'-deoxy 5'-iodo adenosine can efficiently transformed into the corresponding 5',8-cyclo-7,8-dihydronucleoside by zinc in pyridine. Only one diastereoisomer is obtained. By spin decoupling and NOE techniques at 250 MHz, the R-configuration at C-8 was established. This compound showed typical dihedral angles of about 90° for the vicinal protons H-1', H-2' and H-3', H-4'. Using adenosine derivatives stereospecifically labelled at C-5', it was demonstrated that the cyclisation occurs with racemisation at that position.     

An attempt to approach the solutions of the N-electron CNDO hamiltonian for conformational studies of conjugated systems

While dealing with the same N-electron hamiltonian, the SCF approximation and the third order PCILO results completely disagree about the conformation of conjugated systems. An attempt is made, using the CIPSI algorithm, to approach the exact solution of the N-electron CNDO hamiltonian for the butadiene molecule starting from either a priori localized, SCF localized or SCF delocalized MO's. The partial CI's performed from SCF delocalized MO's give arbitrary results when increasing the number of doubly excited determinants and Pancir?'s recent results is fortuitous; on the contrary the results obtained from a priori and SCF localized MO's have better convergence and consistence; from our best calculations the final solution seems to be a rather flat potential curve, the stable minimum being the trans planar minimum, with a second gauche minimum for θ = 120-150° (ΔH ≈ 1 kcal/mole), separated by a weak barrier (ΔH ≈ 2 kcal/mole). The third order PCILO solution is in much better agreement with this estimate of the exact solution than the SCF one.     

Microdetermination of palladium based on formation of ternary complex of palladium with pyrogallol red and cetylpyridinium bromide

A new spectrophotometric method was employed for the determination of microamounts of palladium(II) based on the ternary complex formation with pyrogallol red and cetylpyridinium bromide. A blue green ternary complex, whose molar absorptivities is 22500 mol^?1 cm^?1 at 650 nm, is formed. Composition (PdPGRCP₃) of the ternary complex was established by continuous variation and mole ratio methods. Beer's law range (0.1–8.5 ppm of Pd) and Sandell's sensitivity (0.001 γ/cm²) were evaluated. The conditional stability constant value (logK = 24.35) was determined by Prakash et al. 's method. A detailed study was made for the determination of microamounts of palladium in the presence of platinum metals and several other cations and anions.     

Synthesis and reactions of poly-tetrahydrofuran with azetidinium salt end-groups

The bulk polymerization of tetrahydrofuran (THF) intiated by methyl trillate or triflic anhydride leads to poly-THF's of polydispersity < 1.2 and possessing one or two oxonium chain ends, if the conversion is kept below 15%. Reaction of these “living” polymers with an N-substituted azetidine leads to the corresponding poly-THF's with one or two quaternary azetidinium chain ends. These polymers can be isolated in pure form by precipitation in water without affecting the azetidinium functions. At increased temperature, these functions undergo ring-opening reactions with nucleophiles. This process has been used to prepare block-copolymers and polymer networks containing poly-THF segments and to synthesize mono or bifunctional ester-terminated poly-THF's. The last reaction is achieved by simple precipitation of the azetidinium-terminated poly-THF into an aqueous solution of the sodium carboxylate at room temperature.     

α-Halogenoketones-XII: Extension of the rasoda synthesis of dihydroflavonols

α-Bromo-β-hydroxydihydrochalcones, the intermediates in the Rasoda reaction, were generally available from the reaction of 2'-acetoxychalcones with N-bromo-succinimide in aqueous BuOH and readily cyclized to chalcone epoxides. The base-catalysed recyclization of a 6'-substituted chalcone epoxide gave an aurone and not a trans-dihydroflavonol as was obtained in the absence of a 6'-substituent.     

A concise synthesis of functionalized 2,3-dihydrofuro[3,2-b], [3,2-c], and [2,3-b]pyridines

A strategy for the efficient and rapid one-pot synthesis of 2-aryl-2,3-dihydrofuro[3,2-b], [3,2-c], and [2,3-b]pyridines from readily available o-nitropicolines and aromatic aldehydes is described. The key transformation involves reaction of o-nitropicolines with aromatic aldehydes in the presence of TBAF and Hünig's base giving rise to functionalized products having molecular complexity suitable for further manipulation.     

Preparation of '2,('3)-O-Acyl-pCpA derivatives as substrates for T4 RNA ligase-mediated “chemical aminoacylation”

The synthesis of '2('3)-O-(amino)acyl-pCpA derivatives is described and the products are characterized chemically and as substrates for T4 RNA ligase in the presence of E. coli tRNA ^phe-C_OH. The modified (N-acetylammo)acyl-tRNA's so derived are characterized by their chromatographic and biochemical properties, and by their ability to act as P-site tRNA donors in the peptidyltransferase reaction.     

Dosage spectrophotométrique du molybdène par l'o-phénanthroline

Under certain conditions, o-phenanthroline and its derivatives, as well as 2,2',2′-terpyridyl, form relatively unstable red complexes with molybdenum(Vl) in presence of molybdenum(V). o-Phenanthroline is most sensitive, the molecular extinction coefficient being 6,290 at the absorption maximum (508 mμ). Beer's law is valid for the range 2–9 μg Mo/ml.     

Spectrophotometric study of n,n'-bis(m-sulphobenzyl)dithio-oxamide as a reagent for nickel(II)

N,N'-Bis(m-sulphobenzyl) dithiooxamide forms a water-soluble intensely red chelate with nickel-(II) in buffered solutions at pH 10, A 1 Ni : 1R complex is obtained. The absorption maximum of the complex lies at 500 mμ, where the absorbance of (SB)₂DTO is negligible. The molar extinction coefficient is ca, 6962. Beer's law is obeyed over the range from 0.5 μg to 50 μg per ml.     

NMR and rotational angles in solution conformation of polypeptides

Professor San-Ichiro Mizushima and Professor Yonezo Morino's classical contributions provided unique means and firm basis for understanding of conformational states and internal rotation in polypeptide molecules. Now the NMR spectroscopy is the best choice to study molecular conformation, mechanism of action and structure-functional relationships of peptide and proteins in solution under conditions approaching those of their physiological environments. Crucial details of spatial structure and interactions of these molecules in solution are revealed by using proton-proton and carbon-proton vicinal coupling constants, proton nuclear Overhauser effect and spectral perturbation techniques. The results of NMR conformational analysis are presented for valinomycin “bracelet”, gramicidin A double helices, honey-bee neurotoxin apamin, scorpion insectotoxins and snake neurotoxins of long and short types.     

Raman correlation function for generalized M-diffusion model

A generalized version of Gordon's M-diffusion model for reorientation of molecules in dense phase was proposed by Duttagupta and Sood. They calculated the IR correlation function and compared it with a few experimental data. We calculate the Raman correlation function for this model and compare it with experimental data for OCS, N₂O in CCl₄, and CH₃I. We find that at short times, the agreement with the experimental data is much better than that for Gordon's M-diffusion model. We have also shown that, at long times the correlation function decays as an inverse power of time. However, the experimental correlation function at long times decays much faster.     

2' And 3'-ketonucleosides and their arabino and xylo reduction products: Convenient access via selective protection and oxidation of ribonucleosides

A number of 2',5'- or 3',5'-diprotected ribonucleosides and 5'-protected 2'- or 3'-deoxy-β-D-erythro-pentofuranosyl nucleosides have been oxidized to the corresponding 3' or 2'-ketonucleoside derivatives using chromium trioxide/pyridine/acetic anhydride or dimethyl sulfoxide/ acetic anhydride. Reduction of the carbonyl functions with sodium borohydride gave the inverted arabino, xylo, or deoxy-threo isomers as predominant products by attack at the less hindered α-face of the sugar ring. Parallel reductions using sodium borodeuteride corroborated the epimeric ratios by demonstrating that complete oxidation of the original hydroxyl groups had occurred. The deuterium labeling also aided in making NMR spectral assignments.     

Photoelectron He(I) Spectra of small silanes

The photoelectron He(I) spectra of methyl-, dimethyl-, trimethyl- and ethylsiliane are reported and assigned with the help of CNDO/2 calculations.For each silane the ordering of the valence MO's obtained from calculations is, very close to that of the corresponding alkane, and is in agreement with spectral evidence. Participation of silicon d orbitals in bonding is not substantial but is more important in the outermost SiC and SiH MO's than in the π MO's mainly localized on the alkyl groups.     

Single- and double-gaussian FSGO model and compton profiles

Compton profiles (CP's) calculated from single- and double-gaussian versions of the floating spherical gaussian orbital (FSGO) model are compared with experiment. The CP's calculated from the single-gaussian version die out faster than the experimental CP's due to ill-presented inner shell. The double-gaussian version improves the agreement with the experimental CP's substantially. A remarkable empirical correlation between the molecular energy and the J(0) value as well as the width of the CP, J_0.5, has been observed for the ten-electron series of molecules within the double-gaussian frameworks.