Determination of the Lipophilicity of Bioactive 2-Phenylbenzothiazoles by RPTLC

JPC – Journal of Planar Chromatography – Modern TLC -     

Synthesis of 2,6-Disubstituted Fluorenones

Various 2,6-disubstituted fluorenones 1a-1g were synthesized by the dry salt decomposition of 5,4′ -disubstituted 2-diazoniobenzophenone tetrafluoroborates 8a-8g via Pschorr cyclization in reasonable yields.     

RPTLC Determination of the Lipophilicity of Some New N-[(4-Arylpiperazin-1-yl)alkyl] spirosuccinimides

JPC – Journal of Planar Chromatography – Modern TLC - The lipophilicity of thirty-seven N-[(4-arylpiperazin-1-yl)alkyl]-2- azaspiro[4.4]nonane- and [4.5]decane-1,3-dione derivatives has...     

Synthesis and Mesomorphic Properties of 2,6-Disubstituted Tetralins

Synthesis and mesomorphic behavior of nine members of each of the two classes of 6-phenyl- and 2-phenyltetralins and five members of the 2-trans-cyclohexyltetralins are reported. The synthesis of one member of each class is described in detail. Besides the target compounds, more than twenty intermediates showed liquid crystalline properties; their transition temperatures are recorded (see Tables 1-6).     

RPTLC Determination of the Lipophilicity of 1,2-Benzisothiazol-3(2H)-one Derivatives Substituted in the Heterocyclic Ring

JPC – Journal of Planar Chromatography – Modern TLC - The relative lipophilicity (RM0) and specific hydrophobic surface area of eight 1,2-benzisothiazol-3(2H)-one derivatives...     

Comparison of Reliability of log P Values Calculated from a Group Contribution Approach and from the Autocorrelation Method

Abstract

The values of log P (n-octanol/water partition coefficient) for 1449 chemicals were calculated from the fragmental/regression model of Klopman and co-workers (J. Chem. Inf. Comput. Sci. 1994, 34, 752-781) and from the autocorrelation/backpropagation neural network model implemented in AUTOLOGP_TM (Version 4.0). Both models provided good simulation results but the superiority of the latter was demonstrated.     

Neighboring Group Participation in Glycosylation Reactions by 2,6-Disubstituted 2-O-Benzoyl groups: A Mechanistic Investigation

Variable yields and glycosylation stereoselectivity were obtained for NIS/TfOH-medi- ated reaction of 4-methoxyphenyl 2,4,6-tetra-O-acetyl-β-D-galactopyranoside and thiogalactosides bearing acetyl, benzoyl, 2,6-dimethoxylbenzoyl, 2,4,6-trimethylbenzoyl, or 2,6-dichlorobenzoyl groups at the 2-positions and acetyl at the remainder. X-ray structures of 4-methylphenyl 2,3,4,6-tetra-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D-galactopyr anoside and 4-methylphenyl 3,4-O-isopropylidene-2,6-di-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D-galactopyranoside revealed slightly distorted ⁴ C ₁ chair conformations. Variable temperature NMR revealed that activation of 4-methylphenyl 2,3,4,6-tetra-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D-galactopyranoside afforded only dioxolenium ion, whereas 4-methylphenyl 3,4,6-tri-O-acetyl-2-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D-galactopyranoside gave a 1:1 mixture of dioxolenium ion and glycosyl triflate. However, the reaction intermediates formed from these deactivated donors do not influence the glycosylation stereoselectivity; instead, it is influenced by steric and electronic interactions at the transition states.     

2,6-Disubstituted 4-azidopyrimidines: synthesis,kinetic and thermodynamic studies of azide-tetrazole rearrangement by NMR spectroscopy

Thermodynamic and kinetic parameters of the tautomeric tetrazole-azide rearrangement for a series of 2,6-disubstituted 4-azidopyrimidines are determined by NOESY/EXSY and DNMR: ΔH = 15—28 kJ mol^–1; ΔS = 47—65 J mol^–1 К–1; Е _a = 93—117 kJ mol^–1; lgA = 15.1—18.9. They are dependent on electronic properties of the substituents and the polarity of solvent.     

Replacement of Imine Fragment in the Ring of 2,6-Disubstituted 1,4,3,5-Octathiadiazine-4,4-dioxides in Reaction with Cyano-containing Compounds

Reactions of 2,6-disubstituted 1,4,3,5-octathiadiazine-4,4-dioxides with cyano-containing compounds (nitriles, thiocyanates, N,N-disubstituted cyanamides) proceeding with replacement of imine fragment in dioxide by corresponding fragment of cyanide were investigated. The limits of the reaction were revealed determined by electronic effects of substituents R¹ and R² in dioxide and R³ in cyanide. Transimination occurred in dioxides with strong electron-withdrawing substituents R¹ (CCl₃, CBr₃, C₆F₅) and weak acceptor or donor substituents R²(4-NO₂C₆H₄, 4-ClC₆H₄, CH₃) under the action of compounds R³CN with cyano groups of relatively high nucleophilicity (R³ = 4-ClC₆H₄, C₆H₅, (CH₃)₂CHS, piperidino, morpholino, diethylamino), on the one hand, and with strong electron-withdrawing substituents R³ (CCl₃) on the other hand.     

Comparison of the Activation Energies as Determined by DSC and by Conventional Methods

The results of determination of activation energies (E_A) of polymeric cable insulations obtained by conventional methods (usually based on the evaluation of changes of mechanical properties of insulations after their ageing in thermal chamber at different temperatures) have been compared with results obtained by methods employing the differential scanning calorimetry (DSC). Three DSC methods have been tested: the method according the ASTM E 698; measuring of DSC characteristics in the isothermal mode at several different temperatures; and the method based on evaluation of DSC characteristics of insulations after their thermal ageing in thermal chamber. The last method — which can be called as a modified conventional method, because instead of mechanical properties, the DSC characteristics are determined — has been found as most acceptable and giving similar values of E_A as the other conventional methods. This revised version was published online in August 2006 with corrections to the Cover Date.     

铝-氨羧络合物的表观稳定常数在不同 pH值时的计算值与尿毒症患者血清铝增高的关系

计算了七种 Al-氨羧络合物在不同 pH值下的表观稳定常数,用以解释尿毒症患者血清中铝含量增高的原因,获得了有意义的结果.     

Diastereoselective Synthesis of cis-2,6-Disubstituted Perhydro-4-pyranones Using Elevated Pressure Hydrogenation

A diastereoselective strategy for the synthesis of γ-pyrons was developed, starting from the Mg diacetonedicarboxylate complex. Initial cyclization with suitable anhydrides or acid chlorides, followed by hydrolytic decarboxylation leads to 2,6-disubstituted pyrans. Elevated pressure hydrogenation using Pd/C affords the title compounds in high diastereoselectivity. Scope and limitations of the method are outlined on selected examples.     

The First Homolytic Substitution of Pyrylium Salts. C-4 Methylation of 2,6-Disubstituted Pyrylium Cations

2,6-Diphenylpyrylium and 2,6-di-t-butylpyrylium cations react with methyl radical generated by Bu^tOOH-Fe⁺² in acidic aqueous acetonitrile, to yield substitution exclusively at C-4 position.     

Comparison of Octadecyl-Bonded Alumina and Other Stationary Phases for Lipophilicity Estimation by High Performance Liquid Chromatography

Abstract

A recently developed octadecyl-bonded alumina stationary phase (ODA) was evaluated for determining the lipophilicities of organic compounds by high performance liquid chromatography. Using a column packed with this material and mobile phases consisting of methanol and aqueous buffers, the correlation between the octanol-water partition coefficients (log P's) of compounds of various chemical classes and the logarithms of their chromatographic capacity factors (log k's) was found to be superior to that obtained using columns packed with octadecylsilica, poly butadiene-coated alumina or octadecyl-derivanzed polystyrene-divinylbenzene copolymer. In contrast to results obtained with other columns, phenols and other hydrogen-bonding compounds did not need to be treated as a separate data set on the ODA column to obtain good correlations between log k's and log P's. The resistance of ODA to degradation by alkaline solvents allowed the use of a basic mobile phase (pH > 10) for suppressing ionization and determining the lipophilicities of organic bases which could not be evaluated within the stable pH range of ODS (pH 2–8). The log P's of five basic pharmaceutical compounds determined in this manner were found to be significantly higher than previously reported values. Evidence is presented which indicates that the previously reported log P values of these compounds are inaccurate, due to improper correction for ionization.     

Determination of the Lipophilicity of Some Psychotropic Drugs by RP-TLC

JPC – Journal of Planar Chromatography – Modern TLC - Psychotropic drugs have been chromatographed on RP-18-HPTLC plates with mobile phases containing water, an organic modifier...     

Determination of the Lipophilicity of Xanthines by Reversed-Phase Liquid Chromatography

JPC – Journal of Planar Chromatography – Modern TLC -     

Lipophilicity of oils and fats estimated by TLC

A representative series of natural toxins belonging to alkaloids and mycotoxins classes was investigated by TLC on classical chemically bonded plates and also on oils‐ and fats‐impregnated plates. Their lipophilicity indices are employed in the characterization and comparison of oils and fats. The retention results allowed an accurate indirect estimation of oils and fats lipophilicity. The investigated fats and oils near classical chemically bonded phases are classified and compared by means of multivariate exploratory techniques, such as cluster analysis, principal component analysis, or fuzzy‐principal component analysis. Additionally, a concrete hierarchy of oils and fats derived from the observed lipophilic character is suggested. Human fat seems to be very similar to animal fats, but also possess RP‐18, RP‐18W, and RP‐8.