Regio- and stereoselectivities in Diels-Alder cyclodimerizations of orthoquinonoid cyclohexa-2,4-dienones

The [4+2] cyclodimerization of cyclohexa-2,4-dienone derivatives of the orthoquinone monoketal and orthoquinol types has been the topic of numerous investigations over the last 50 years in the aim of rationalizing the extraordinary level of regio-, site-, and stereoselectivities observed in these processes. In particular, the double diastereo-π-facial differentiation expressed in cyclodimerizations of chiral orthoquinols (i.e., 6-alkyl-6-hydroxycyclohexa-2,4-dienones) is an important aspect of these transformations, for they relate to the construction of several natural products. The experimental and theoretical results that are described in this article offer a comprehensive understanding of the factors controlling these site-specific regio- and diastereoselectivities. Our interpretation of these results relies on a combination of Woodward-Hoffmann and Salem-Houk secondary orbital interactions and Cieplak-type hyperconjugative effects in bispericyclic C₂-symmetric transition states.     

New method for the preparation of O-carbamoyl derivatives in the 4-hydroxyaminoimidazolidin-2-one series

The corresponding 4-(O-carbamoylhydroxyamino)imidazolidin-2-ones were obtained by cyclization of O,N-dicarbamoyl derivatives of N-(3-oximino-2-methyl-2-butyl)- and N-(1-oximino-2-cyclohexyl)methylamines in alkaline media. It was shown that the carbamoylation of 1-methyl-4,5-tetramethylene-3-(3,4-dichlorophenyl)-4-hydroxy-aminoimidazolidin-2-one gives, respectively, an O- or N-carbamoyl derivative, depending on whether it is carried out in alkaline or neutral solutions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 399–401, March, 1984.     

Characterization and TLC-Bioautographic Detection of Essential Oils from Some Thymus Taxa. Determination of the Activity of the Oils and their Components Against Plant Pathogenic Bacteria

JPC – Journal of Planar Chromatography – Modern TLC - The chemical composition of the oils of four thyme (Lamiaceae) chemotypes (Thymus vulgaris L., Thymus serpyllum L., Thymus x...     

Methyl cellulose-based edible films and coatings I. Effect of plasticizer content on water and 1-octen-3-ol sorption and transport

Edible films were prepared from methyl cellulose with various concentrations of poly(ethylene glycol) 400 (PEG400) used as a plasticizer. Water vapour and 1-octen-3-ol (an aroma compound) were selected as hydrophilic and hydrophobic volatile penetrants respectively. Their solubility and permeability through methyl cellulose-based edible films were studied using gas chromatography methods. Whatever penetrant was used, the flux increased with the PEG400 content. Transfer behaviour, i.e., the order of increased magnitude of the transfer rate, strongly depends on the nature of the volatile compound. However, water sorption only depends on the PEG400 content whereas the aroma compound sorption is affected by both the water and the PEG400 concentrations. Relationships between solubility and permeability can be partially explained by the plasticization phenomenon.     

Investigations into functionally substituted azines.

Reaction of 2-N-potassiocyanamino-4,6-bisisopropyl(dimethylamino)-sym-triazines with acid 1,2,2,2-tetrachloroethylamides leads to the formation of 2-N-cyano-N-(1-acylamino-2,2,2-trichloroethyl)amino-4,6-bisisopropyl(dimethylamino)-sym-triazines. Reaction with 1-hydroxy(methoxy)-2,2,2-trichloroethylamides of chloroacetic acid leads to 2-(2-imino-4-oxooxazolidin-1-yl)-4,6-bis(dimethylamino)-sym-triazine and its 1-methoxy-2,2,2-trichloroethyl derivative substituted at the position 3 of the oxazolidine ring.     

Synthesis and thermal decomposition of haloalkoxy-sym-triazines. 8. Synthesis and thermal decomposition of 2-methoxy(methylthio)-4-(2-chloroethylthio)-6-dialkylamino-sym-triazines

New 2-chloroethylthio derivatives of sym-triazine were obtained by the reaction of mercapto-sym-triazines and dichloroethane. It was established that these chlorides undergo cyclization to give 2-dialkylamino-4-oxo(thioxo)-4,5,6,7-tetrahydrothiazolo [1,2-a]-sym-triazines, the structure of which was confirmed by PMR and mass-spectral data, at moderate temperatures.See [7] for Communication 7.Translated f rom Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1275–1278, September, 1981.     

The adsorption of endothelin 1 to phospholipids is governed by electrostatic interactions: A monolayer and fluorescence study

In order to elucidate the influence on the lipidic environment on the recognition process of its membrane associated receptor, the interactions of the vasoconstrictor peptide endothelin 1 with various phospholipids have been investigated using different lipidic model membranes: monolayers at constant surface pressure, vesicles and micelles. A monolayer study of ET1 adsorbed onto the water surface has shown that the C-terminus of the peptide points towards the aqueous phase. Penetration measurements into lipidic monolayers indicate that ET1 adsorbs to phospholipids with an orientation similar to that of the air–water interface and fluorescence measurements are in agreement with such an orientation of the peptide. This adsorption is selective for neutral phospholipids and indicates that the nature of the phospholipid headgroups is of major importance for the approach of the membrane associated receptor.     

Quaternization of tetrazoles under high pressure and establishment of the structures of quaternary tetrazolium salts by 13C NMR spectroscopy

The quaternization of 1- and 2-acetonyl-5-R-tetrazoles, as well as dimethyltetrazole, was accomplished under high pressure conditions (5000–14,000 kgf/cm²) by means of bromoacetone and methyl iodide and at atmospheric pressure and room temperature under the influence of methyl fluorosulfate. The structure of the salts were ascertained by ¹³C NMR spectroscopy, and the principles of the change in the chemical shifts and the spin-spin coupling constants during quaternization and protonation of the tetrazoles were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1118–1124, August, 1982.     

Full verification of the liquid exclusion-adsorption chromatography theory using monolithic capillary columns

Capillary electrochromatography (CEC) was used to separate alkyl phenol ethoxylates (APEs) as model diblock copolymers, with monolithic polymers as stationary phases. The order of elution indicate that the two polymer blocks follow distinct chromatographic modes: size-exclusion for the poly(oxyethylene) group and adsorption interaction for the alkyl part. Therefore, our experimental results were compared to the theory describing liquid exclusion-adsorption chromatography (LEAC). They were found in perfect agreement with the theory, which turned to be verified for the first time over the full range of polymer lengths.