Synthèse des pyrido[2,3-d] el [3,2-d] -s-triazolo[3,4-f] pyrimidines el de (pyrazolyl-1')-4 pyrido[2,3-d] et [3,2-d] pyrimidines

The synthesis of two new heterocycles is described: pyrido-[2,3-d]-.s-triazolo[ 3,4-f] pyrimidine and pyrido[3,2-d]-.s-triayzolo-[3,4-f] pyrimidine. 4-[I'-Pyrazolyl]pyrido[2,3-d]pyrimidines and 4-[1′-pyrazoly1] pyrido[ 3,2-d] pyrimidine are obtained by the action of 4-hydrazinopyrido[2,3-d]pyrimidine and 4-hydrazinopyrido-[3,2-d]pyrimidine with several β-diketones.     

Studies on new routes for the synthesis of 4- and 5-aminoimidazole nucleoside derivatives

The synthesis of urethane protected 4- and 5-aminoimidazole nucleoside derivatives 4 and 9 by two different routes is described. These routes are transformation of the carboxylate substituted imidazole nucleoside 1 via a Curtius rearrangement to give 4 and direct ribosylation of the imidazole base 6 to give a mixture of positional isomers 7 and 8 , which by deacetylation afford 4 and 9 , respectively. The convenience of each route depended on the positional isomer to be synthesized.     

New antitumour active platinum compounds containing carboxylate ligands in trans geometry: synthesis, crystal structure and biological activity

New asymmetric trans-platinum(II) complexes, composed of an isopropylamine, an azole and two carboxylate leaving groups, are presented. The crystal and molecular structures of one of the complexes has been determined and the cytotoxicity and reactivity with 5'-guanosine monophosphate is reported. The complexes show a reduced reactivity, but no decrease in cytotoxic activity compared to their chloro-counterparts. Furthermore the complexes largely overcome cisplatin resistance, they therefore present an interesting class of antitumour active trans-platinum complexes.     

delta-Lactone from Oedogonium capillare and their effects on rat ileum

Antispasmodic activity-guided fractionation together with chemical analysis led to the isolation of one novel delta-lactone named oedogonolide from Oedogonium capillare. Identification was based on spectroscopic methods. The oedogonolide produces a significant antispasmodic effect on the contractions of the rat ileum induced by acetylcholine, histamine and barium chloride.     

Shear modulated percolation in carbon nanotube composites

A novel time-dependent percolation transition has been observed in sheared carbon nanotube (CNT) composites. At a fixed CNT filler loading, the electrical conductivities of CNT composites can change abruptly as much as 8 orders of magnitude as the shear processing time increases. Microstructure characterization shows that the CNTs have aligned along the shear flow direction, which leads to the dramatic increase of the percolation threshold and thereby the dramatic decreases of the electrical conductivities. Our results highlight the great importance of understanding the response of CNT dispersion states to the processing conditions.     

On the propagation of random electromagnetic fields with position-independent stochastic behavior

A certain kind of vectorial fields with position-independent stochastic behavior is introduced, for which several main features are preserved upon free propagation. For this set of random electromagnetic fields, it is shown that the uniform degree of polarization, the maximum attainable visibility in a Young experiment, and the expansion of the cross-spectral density tensor as the sum of totally-polarized and unpolarized terms are properties that apply for any propagation distance. An elementary example is also shown.     

A new entry to enantiopure polysubstituted cyclopropanes: stereoselective denitrogenation of sulfinylpyrazolines under Yb(OTf)3 catalysis

[Structure: see text] Chemoselective and completely stereoselective denitrogenation of optically pure pyrazolines, derived from 3-sulfinylfuran-2(5H)-ones, into cyclopropanes can be achieved under substoichiometric Yb(OTf)3 catalysis. Reactions evolve in almost quantitative yields with complete retention of the configuration at both carbons flanking the nitrogen atoms. The resulting enantiomerically pure polysubstituted cyclopropanes, containing up to five substituens, can be desulfinylated with Ra-Ni providing polysubstituted cyclopropanecarboxylic acid derivatives.     

Stochastic comparisons for time transformed exponential models

Different sufficient conditions for stochastic comparisons between random vectors have been described in the literature. In particular, conditions for the comparison of random vectors having the same copula, i.e., the same dependence structure, may be found in Müller and Scarsini (2001). Here we provide conditions for the comparison, in the usual stochastic order sense and in other weaker stochastic orders, of two time transformed exponential bivariate lifetimes having different copulas. Some examples of applications are provided too.