Aminothiazole derivatives. I. A convenient synthesis of monocyclic and condensed 5-aminothiazole derivatives

Treatment of diamides derived from α-amino acids with phosphorus pentasulfide or Lawesson's reagent was shown to provide a convenient method to prepare 5-aminothiazoles. By this method, in addition to mono-cyclic 5-aminothiazoles 19 , novel bicyclic 5-aminothiazole derivatives such as 4,5,6,7-tetrahydrothiazolo[5,4-b]pyridines 11 , 5,6,7,8-tetrahydro-4H-thiazolo[5,4-b]azepines 7 , 4,5,6,7,8,9-hexahydrothiazolo[5,4-b]azocine 16 and related compounds were prepared in moderate to good yields from simple diamides, suggesting the wide versatility of the method.     

Determination of Heraclenin and Heraclenol in Heracleum candicans D.C. by TLC

A simple TLC method has been developed for the simultaneous determination of heraclenin and heraclenol in the roots of Heracleum candicans D.C. The analytes were separated on silica gel F₂₅₄ plates with toluene:ethyl acetate (7:3) and scanned using densitometry at 366 nm. The method was validated in terms of precision, repeatability and accuracy. The linear range for heraclenin was found to be 4 - 10 μg per spot with correlation coefficient of 0.997 while for heraclenol it was 1–5 μg per spot with a correlation coefficient of 0.985. The two compounds were quantified in different samples of H. candicans and were found to be present in the range of 1.02 – 1.36% and 0.29 – 0.43% w/w. The method was found to be very simple, accurate, precise and economical and can be used for routine quality control.     

Calculation of j and jm symbols for arbitrary compact groups. I. Methodology

A systematic method is established for computing the coupling coefficients associated with arbitrary compact groups using only the general properties of the coefficients and the specific character theory of the relevant groups. The basic character theory is first outlined. Then a primitive set of 6j symbols is defined and their computation sketched with careful attention being given to matters of phase fixing. A recursive method is developed for calculating arbitrary 6j symbols using the primitive set. Finally, a primitive set of 3jm factors is set up and then the general 3jm factors computed recursively.     

Molecular symmetry and ab initio calculations. II. Symmetry-matrix and symmetry-supermatrix in the Dirac-Fock method

The concepts of symmetry-matrix and symmetry-supermatrix introduced in article I [J. Comput. Chem., 10, 957 (1989)] can be generalized to the Dirac-Fock method. By using the semidirect product decomposition of O_h and the linear vector space theory, the irreducible representation basis of O_h for any molecular system (O_h or its subgroups) can be deduced analytically in the nonorthonormal Cartesian Gaussian basis. This method is extended to discuss the double-valued representations of O_h* in the complex Cartesian Gaussian spinor basis. In the double-valued irreducible representation basis of D₂*, the matrix of kinetic operator c(OVERLINE)σ(/OVERLINE)·(OVERLINE)p(/OVELINE) in the Dirac-Fock equation can be reduced into a real symmetric and can be grouped into classes under the operations in D_3d. Therefore, the symmetry-matrix and symmetry-supermatrix can also be used in the Dirac-Fock method to reduce the storage of two electron integrals and calculations of Fock matrix during iterations by a factor of ca. g² (g is the order of the molecular symmetry group). In addition, a method to deal with the nonorthonormal space is presented. © 1996 by John Wiley & Sons, Inc.     

Quantitative RP–LC Analysis of Mangiferin and Homomangiferin in Mangifera indica L. Leaves and in Mangifera persiciforma C.Y. Wu et T.L. Ming Leaves

Mangiferin is a pharmacologically active flavonoid, a natural xanthone C-glycoside. Homomangiferin is mangiferin monomethyl ether. Mangiferin and homomangiferin have important medicinal properties and are widely used to relieve many symptoms, for example coughing and asthma. A new gradient reversed-phase high-performance liquid chromatographic method has been developed for analysis of these compounds. The amounts of mangiferin and homomangiferin in 20 samples of Mangifera indica L. leaves and in five samples of M. persiciforma C.Y. Wu et T.L. Ming leaves were quantified by use of the method. The method was validated for system suitability, precision, accuracy, and linearity. The average recovery of the method at three levels was 98.7–101.5% and linearity was good (r > 0.9998) for both mangiferin and homomangiferin over a relatively wide range of concentration. The amounts of the two flavonoid compounds in M. indica L. leaves of different species or collected in different months, and in M. persiciforma C.Y. Wu et T.L. Ming leaves from different collection sites were evaluated in this study and the differences are discussed.

     

A comparative study of Mentha arvensis L. and Mentha haplocalyx Briq. by HPLC

We have developed a new method to simultaneously determine five marker compounds in Menthae Herba via HPLC/PDA – including hesperidin (1), rosmarinic acid (2), diosmin (3), didymin (4) and buddleoside (5). The newly developed method was successfully used to analyse for two species (Mentha arvensis L. and Mentha haplocalyx Briq.) of Menthae Herba, and the satisfactory results were obtained from the validation of developed method. The pattern analysis could greatly discriminate between M. arvensis L. and M. haplocalyx Briq. In conclusion, the proposed HPLC/PDA method is suitable for quality evaluation of Menthae Herba.     

Reactivity and gelation. I. Intrinsic reactivity

The method of Case is used with the Flory-Stockmayer gelation criterion to derive a critical transition equation for polycondensation of multifunctional reactants bearing coreactive functional groups of two species A and B, where the B groups may be of unequal intrinsic reactivity. Systems of the types R(A)₂/R′(B)₄ and R(A)₂/R′(B)₄/R′′(B)₂ are considered with the B groups divided into two classes characterized by a reactivity ratio in the range 0.1 to 10. If the reactivities are sufficiently different the polymerization can be regarded as a multistage process. Intramolecular reactions are not considered.     

Geometry and energy of overcrowded ethylenes. II. Bornanylidene,fenchylidene, and bifluorenylidene derivatives

The geometry and energy of some bornanylidene, fenchylidene, and bifluorenylidene derivatives have been determined by the molecular mechanics method. Low twisting of the double bond was found for the compounds of the first two series. The difficulties found in the synthesis of 2-di-tert-butylmethylenefenchane can be related to a remarkable strain energy which is only slightly lower than that of tetra-tert-butylethylene. A twisted conformation is the preferred one in bifluorenylidene and its 1,1′-dimethyl derivative (E isomer) in agreement with experimental data. Conformational inversion and E–Z interconversion paths are discussed for the latter compound and theoretical results are compared with dynamic NMR data.     

Qualitative and quantitative analysis of phenolic acid glycosides in Ginkgo biloba L. leaf,G. biloba leaf extract and its injection

Ginkgo biloba L. leaf (GBL) is one of the most commonly used medicinal plants in the world. Phenolic acids with biological activities have a relatively high content in G. biloba leaf extracts (GBE); therefore they are of great significance for the quality control of GBL, GBE and its preparations. However, there have been few studies focused on their analysis. In this work, 12 phenolic acids, including 11 phenolic acid glycosides, were identified by liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (LC–Q-TOF/MS). Then, a method combining enzymolysis with HPLC was established for quantification of phenolic acid glycosides. It was found that the aglycones of phenolic acid glycosides mainly comprised five phenolic acids: 2,4,6-trihydroxybenzoic acid, protocatechuic acid, p-hydroxybenzoic acid, vanillic acid and p-coumaric acid. The quantitative method was validated, and the correlation coefficient (0.9993–0.9999), recovery (≥88.4%), repeatability (≤0.8%), and inter-day precision (≤5.5%) were satisfactory. Finally, the contents of glycosides of five phenolic acids in GBL, GBE and GBE injection from different sources were determined by the developed method. The method was accurate, repeatable and practicable, which could be helpful for the quantification of phenolic acid glycosides in other products containing GBL or GBE.     

13C n.m.r. spectra of some thiobenzamides. Correlation between 13C and 1H n.m.r. spectra and signal assignments of syn and anti CH2 groups

¹³C n.m.r. spectra of a series of N,N-disubstituted thioamides have been recorded and signal assignments were performed. Separate signals are observed for methylene groups fixed on the nitrogen atom. Since the carbon atom syn to the thiocarbonyl sulfur resonates at higher field than the anti carbon, the syn-anti assignment in ¹H n.m.r. is easily obtained by selective double irradiation. This method, which is rapid and reliable, affords a rather general solution to the interesting problem of resonance assignments in tertiary amides and thioamides (and in analogous molecules such as oximes and nitrosamines).     

Dyad algebra and multiplication of graphs. II. Undirected graphs

In paper I abstract vectors |e>, their adjoints <e|, dyads such as |e><e|, and abstract linear operators were related to graphs which are in general directed. With an Hermitian operator one gets equivalence classes of undirected graphs with or without loops and multi-lines. The present paper II gives rules for the multiplication of such graphs based on their underlying dyad algebra. The results may be used in the evaluation of the outcome of successive applications of operators for observables as in the case of the powers of a one-electron Hamiltonian in the method of moments, or in using projection operators, electron density, and the like.     

Nucleosides and Nucleotides. Part 17. A simple preparation of protected deoxynucleoside-3'-phosphates

A simple method for the preparation of fully protected 2′-deoxynucleoside-3′-phosphates is described. The main step, phosphorylation of partially protected deoxynucleosides, is performed with the monofunctional reagent p-chlorophenyl (2-cyanoethyl) phosphochloridate³) ( 2 ) in dioxane. This reagent is quickly prepared from readily accessible p-chlorophenyl phosphodichloridate by reaction with 3-hydroxypropionitrile and triethylamine in dioxane or ether. The crude reagent is used directly for phosphorylation. After chromatography, protected deoxynucleoside-3′-phosphates were isolated in yields of 80–87%. The method described here, which has been optimized in detail, represents a simple alternative to published methods.     

Molecular weights and molecular weight distribution of polymers by equilibrium ultracentrifugation. Part II. Molecular weight distribution

A method has been developed for determining the molecular weight distribution of a polymer sample from the sedimentation–diffusion equilibrium data for a solution under pseudo-ideal conditions. From some theoretical examples it appears that the method works well and that the molecular weight distribution can be determined with a reasonable degree of resolution. From three polymer samples (polyethylene, polystyrene, and polycaprolactam) the molecular weight distribution was determined in this way. The average molecular weights, M?_n, M?_w, M?_z, and M _z+1, calculated from these distribution functions agree well with those calculated directly from the equilibrium data.     

Benzo[b]thiophene derivatives. XXV. Condensation and reductive alkylation of 3-aminoalkylbenzo[b]thiophenes with formaldehyde

The reductive alkylation of 3-aminomethylbenzo[b]thiophene by the Eschweiler-Clarke (formaldehyde-formic acid) method and of 3-β-aminoethylbenzo[b]thiophene by the Borch (formaldehyde-cyanoborohydride) method proceeded in good yields. However, the Eschweiler-Clarke reaction with 3-β-aminoethylbenzo[b]thiophene gave the Pictet-Spengler cyclized product, N-methyl-1,2,3,4-tetrahydrobenzo[b]thieno[2,3c]pyridine. Mechanistic aspects of the latter reaction were investigated.     

Properties of amphoteric polyurethane waterborne dispersions. III. Isoelectric points and precipitation

The isoelectric points of amphoteric polyurethane (APU) with hydrophobic soft segments and pendent ? COOH and ? CH₂N(CH₃)₂ groups and the effect of inorganic salts on the isoelectric points were investigated by the conductivity titration method. The pH values at isoelectric points agreed with the theoretical isoelectric point equations of Patrickios and Merle with pK_a = 6.1 and pK_b = 8.3, even though, as an ionomer, APU has a low density of ionizable groups on the macromolecular chains and takes a micellar state in aqueous media. The precipitation of APU waterborne dispersions also was observed around the isoelectric points and around lower or higher pH values with the ultraviolet spectrophotometric method. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2440–2448, 2002     

HPLC/MS analysis of polyphenols,antioxidant and antimicrobial activities of Artabotrys hildebrandtii O. Hffm. extracts

The purpose of this work was to evaluate chemical constituents, antioxidant and antimicrobial activities of Artabotrys hildebrandtii, an endemic medicinal plant from Madagascar. Ethanol extracts from the leaves and stem bark were tested to evaluate DPPH free radical scavenging, using butylated hydroxytoluene and quercetin as standard antioxidants. An high-performance liquid chromatography/mass spectrometry method was developed to investigate the presence of phenolic compounds in the studied samples; gentisic acid, chlorogenic acid, hyperoside, isoquercitrin, rutin, quercitrin, quercetol, apigenin and luteolin were identified. Total polyphenolic content was determined by a spectrophotometric method using Folin–Ciocâlteu reagent. Results showed the efficiency of A. hildebrandtii leaves extract against strains of Staphylococcus aureus and Listeria monocytogenes, as the inhibitory activity is more powerful compared to Gentamicin, used as the standard drug. The leaves of A. hildebrandtii can be considered an important source of polyphenols, especially of rutin, with good antioxidant and antimicrobial activities.     

Enamines. III. A theoretical and photoelectron spectroscopic study of the molecular and electronic structures of aziridine enamines

The photoelectron (PE.) spectra of N-vinylaziridine ( 1 ) and some methyl and ethyl substituted derivatives are discussed in the light of quantum-chemical model calculations using the PRDDO SCF method. All aziridine enamines are found to exist as equilibrium mixtures of variable compositions, with an enamine-type conformation ( I ) generally as the major and a trans-bisected form (II) as the minor component.     

Reactions of the nitrosonium ion. VII. Syntheses of dihydroisoquinolines and oxazoles from azides in nitrile solvents

N-Alkylnitrilium salts are cleanly produced from alkyl azides by reaction with nitrosonium salts in nitrile solvents. Syntheses of 3,4-dihydroisoquinolines from nitrilium ions formed in this method from 2-phenylethyl azide are described. Oxazoles are readily formed from phenacyl azides by this general method; the advantages of oxazole syntheses through azide nitrosation are discussed.     

Components and antioxidant activity of fruits of Cirsium palustre and C. rivulare

In the hexane extract of C. palustre and C. rivulare fruits, fatty acids, sterols, triterpenes, and volatile compounds were analyzed by the GC-MS-FID method. In the methanolic extracts, total phenol content was estimated. The antioxidant activity of both extracts was measured with DPPH assay and expressed in % scavenged DPPH.     

Polymerization mechanisms and molecular weight distribution. I. Mathematical treatment

A novel method for determining the polymerization mechanism and the kinetic rate constants from the molecular weight distribution is proposed. The particular criterion function used as basis for parameter adjustment is where θ is the vector of dependent variables, y(r, θ) is the theoretical molecular weight distribution for the assumed polymerization mechanism, and y_E(r) is the experimental molecular weight distribution which is a function of the chain length r. A form of the gradient method of optimization was used to solve the criterion function. The proposed method is particularly powerful since the whole molecular weight distribution is utilized.