Reusable photoresponsive Ag/AgCl nanocube-catalyzed one-pot synthesis of seleno[2,3-b]pyridine derivatives

Research on Chemical Intermediates - In this study, a facile and rapid method was developed to synthesize intensely organoselenium compounds, namely ethylseleno[2,3-b]pyridine carboxylate,...     

A convenient green synthetic approach to the synthesis of novel bioactive selenolo[2,3-c]pyrazoles as antibacterial and antifungal agents

A series of new pyrimidine, triazine, and isoindole heterocycles fused to the selenolopyrazole ring system was synthesized by various condensation reactions of the amino selenolopyrazole carboxamide 1 , which was performed by a new green methodology. The pyrimidinone compound 6 was used as a versatile precursor for several aromatic nucleophilic substitution reactions to produce the sulfanyl pyrimidines 10a-c and the corresponding amines 11a-c and 12a , b . Assignment of the chemical structures for the newly synthesized compounds was confirmed by elemental and spectral analyses including Fourier transform infrared (FTIR), ¹H-NMR, and ¹³C-NMR and mass spectroscopy for some of them. Furthermore, some of these compounds were screened against various pathogenic bacterial and fungal strains. Their results demonstrated that some of them revealed remarkable antimicrobial activities.     

On countable completions of quotient ordered semigroups

A poset is said to be ω-chain complete if every countable chain in it has a least upper bound. It is known that every partially ordered set has a natural ω-completion. In this paper we study the ω-completion of partially ordered semigroups, and the topological action of such a semigroup on its ω-completion. We show that, for partially ordered semigroups, ω-completion and quotient with respect to congruences are two operations that commute with each other. This contrasts with the case of general partially ordered sets.     

Crystallization kinetics of poly(ethylene oxide) from its melt and from mixtures with tetrahydronaphthalene and oligo(ethylene oxide‐block‐dimethylsiloxane)

The crystallization of poly(ethylene oxide) (PEO) from the pure state and from its mixtures with oligo(dimethyl siloxane‐b‐ethylene oxide) (COP) and tetrahydronaphthalene (THN) was investigated. The crystallization kinetics was studied isothermally and nonisothermally with an automated device that monitored the light passing through the corresponding liquids as functions of time and/or temperature. The rate was strongly influenced by the concentration of COP in the mixture. A substantial decrease in the induction time (the time required for the onset of crystallization) and a considerable shift in the crystallization temperature (the transition from a liquid state to a solid state) to higher temperatures were observed as the concentration of COP rose. This behavior was attributed to the differences in the interaction parameters of PEO with THN and COP. The isothermal crystallization kinetics was analyzed on the basis of the Avrami equation. Modified approaches (Avrami and Ozawa) were used for the evaluation of nonisothermal crystallization. In the initial state of crystallization, a power law held true for the augmentation of the radii of spherulites with time for all mixtures, regardless of the concentration of COP. Different spherulitic morphologies were observed, depending on the COP concentration. With rising COP contents, the structures changed from being needlelike to being compact. These findings were all examined in terms of the isothermal variation of the degree of supercooling resulting from changes in the compositions of the mixtures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 820–829, 2004     

Hexafluoroacetone as Protecting and Activating Reagent. A New Approach to <Emphasis Type="Italic">N</Emphasis>-linked Glycopeptoids

Summary. A preparatively simple synthesis of N-linked glycopeptoids starting from iminodiacetic acid and glycosylamines, using hexafluoroacetone as protecting and activating reagent is described.     

Synthetic studies on stevastelins. 2. Synthesis of lipidic- and peptidic-modified analogues

[Chemical reaction: See text] The synthesis of a series of stevastelin analogues with modification of the susbstituent at the C-2 position of the stearic acid chain (compounds 28 and 31), variation of the amino acids (compounds 41, 42, 73, and 78), or lacking the lipidic chain (compound 91) is described. The replacement of L-valine and L-threonine with other amino acids proceeded without difficulties for the synthesis of analogues 41 and 42; however, the substitution of L-serine with simple amino acids, such as glycine or L-alanine, proved to be elusive, which was adscribed to factors of conformational flexibility. Finally, the substitution with L-valine or L-threonine proceeded without difficulties to provide the analogues 73 and 78 respectively.     

ACTIVATED NITRILES IN HETEROCYCLIC SYNTHESIS: NOVEL SYNTHESIS OF PYRROLO[1,2-c]IMIDAZOLE AND PYRANO[2,3-d]IMIDAZOLE DERIVATIVES

Abstract

Several new pyrrolo[1,2-ylidene ethyl cyanoacetate (lc, d) with each of (2) and (11) afforded the 5-ylidene-2-thiohydantoins (Sa, b), (Wn. b) respectively. Compounds Sn, b react with each of malononitrile and ethyl cyanoacet-ate to give the corresponding pyrroloimidazole derivatives (h,b) and (an, b) respectively. The structure of the isolated products were established by elemental analyse and spectral data studies.