2,970 research outputs found
Six-membered ring systems: with O and/or S atoms
The most interesting chemistry published in 2020 on the synthesis of O- and S-six-membered heterocycles is reviewed. This personal overview is focused on the developments made on the synthesis of a large variety of natural compounds, specific reactions, and reagents for the preparation of natural and synthetic pyrans, chromenes and chromans, isochromenes and isochromans, pyranones, coumarins and isocoumarins, chromones and chromanones, xanthenes and xanthones, thiopyrans and analogues, dioxanes, dithiins, and also oxathianes.info:eu-repo/semantics/publishedVersio
A 31P nuclear magnetic resonance study of phosphate levels in roots of ectomycorrhizal and nonmycorrhizal plants of Castanea sativa Mill.
31P-Nuclear Magnetic Resonance (NMR) was
used to assess phosphate distribution in ectomycorrhizal and nonmycorrhizal roots of Castanea sativa Mill. as well as in the mycorrhizal fungus Pisolithus tinctorius in order to gain insight into phosphate trafficking in these systems. The fungus P. tinctorius accumulated high levels of polyphosphates during the rapid phase of growth.
Mycorrhizal and nonmycorrhizal roots accumulate orthophosphate. Only mycorrhizal roots presented polyphosphates. The content in polyphosphates increased along the 3 months of mycorrhiza formation. In mycorrhizal roots of plants cultured under axenic conditions, the orthophosphate pool decreased along the culture time. In nonmycorrhizal roots the decrease in the orthophosphate content was less pronounced. The level of orthophosphate in mycorrhizal roots was significantly lower than in nonmycorrhizal ones, which indicates that this system relies upon the fungal polyphosphates as a major source of phosphate
A Multiple Criteria Framework to Evaluate Bank Branch Potential Attractiveness
Remarkable progress has occurred over the years in the performance evaluation of bank branches. Even though financial measures are usually considered the most important in assessing branch viability, we posit that insufficient attention has been given to other factors that affect the branches’ potential profitability and attractiveness. Based on the integrated used of cognitive maps and MCDA techniques, we propose a framework that adds value to the way that potential attractiveness criteria to assess bank branches are selected and to the way that the trade-offs between those criteria are obtained. This framework is the result of a process involving several directors from the five largest banks operating in Portugal, and follows a constructivist approach. Our findings suggest that the use of cognitive maps systematically identifies previously omitted criteria that may assess potential attractiveness. The use of MCDA techniques may clarify and add transparency to the way trade-offs are dealt with. Advantages and disadvantages of the proposed framework are also discussed.
Epoxidação de (E,E)-Cinamilidenoacetofenonas com Peróxido de Hidrogénio
As (E,E)-cinamilidenoacetofenonas pertencem a um importante grupo de
cetonas a,β,Y,∂-insaturadas, cuja síntese envolve a condensação aldólica de
acetofenonas com cinamaldeídos adequadamente substituídos.
Certos derivados saturados, as 1,5-diaril-1-pentanonas, foram isolados a partir
de plantas usadas na medicina tradicional da Africa tropical, da Ásia e da Austrália
e demonstraram possuir forte actividade anti-bacteriana.2 No entanto, os compostos
desta família com mais aplicações são as (E,E)-2'-hidroxicinamilidenoacetofenonas,
as quais constituem uma importante classe de intermediários na síntese de 2-
estirilcromonas.3
A epoxidação deste tipo de compostos com dimetildioxirano ou com o método
de epoxidação assimétrica de Juliá já foi descrita, embora neste último caso se tenha
utilizado um só derivado.4 Tendo em conta o nosso estudo da reactividade de (E,E)-
cinamilidenoacetofenonas e a potencialidade dos epóxidos obtidos na síntese duma
grande variedade de novos compostos, decidiu-se estudar o efeito da utilização do
catalisador de salen Mn(III) na epoxidação da (E,E)-cinamilidenoacetofenona 1a
usando o H2O2 como oxidante
Novel Hydroxy-9H-xanthen-9-ones derivatives: synthesis and bioactive properties
9H-Xanthen-9-ones commonly referred as xanthones are a large group of natural heterocyclic compounds with significant bioactive properties (e.g. anti-inflammatory, antibacterial, antimalarial, cytotoxicity and radical scavenging activity).1 In order to explore some of these biological assessments, we developed two methodologies for the synthesis of novel hydroxylated 2,3-diarylxanthone derivatives. The first synthetic route is based on the Heck reaction of the 3-bromochromone 2 followed by aldol condensation and electrocyclisation/oxidation processes to afford the 2,3-diaryl-9H-xanthen-9-ones 1. An efficient and more general approach is the Heck reaction of 3-bromo-2-styrylchromones 3 with styrenes as olefins followed by the in situ electrocyclisation/oxidation processes.2 Pharmacological studies involving the hydroxy-9H-xanthen-9-ones 1,3 which are obtained after cleavage of the methyl group, will also be presented and discussed
Synthesis of new hydroxy-2-styrylchromones
http://apps.isiknowledge.com/full_record.do?product=UA&search_mode=GeneralSearch&qid=5&SID=V1M67gPH3IpI7j5a98j&page=1&doc=1&colname=WOSHydroxy-2-styrylchromones 5a−i were prepared by debenzylation
of benzyloxy-2-styrylchromones 3a−i, which
were synthesised by the Baker−Venkataraman method. The
last step of this method, the cyclodehydration 5-aryl-3-hydroxy-
1-(2-hydroxyaryl)-2,4-pentadien-1-ones 2a−i, was carried
out with a catalytic amount of iodine, or p-toluenesulfonic
acid, in DMSO. Benzyloxy-3-cinnamoyl-2-styrylchromones 4a−f were obtained as by-products in both procedures,
but the latter procedure gave benzyloxy-2-
styrylchromones 3a−i in better yields. The structures of all
new compounds were established by extensive NMR studies
Explicit group USSOR method for solving elliptic partial differential equations
This paper presents a new 4-points Explicit Group Unsymmetric
Successive Overrelaxation (USSOR) iterative method to approximate the solution of the
linear systems derived from the discretisation of self-adjoint elliptic partial equations.
Several studies have been carried out by many researchers on the USSOR iterative
method, for example, the analysis of its convergence [1], an upper bound for its error [2]
and recently a special case of the USSOR, namely the SSOR method has been used to
approximate the solution of augmented systems [4] and [8]. The computational behaviour
of this new method and a comparison with its point version is presented
Stationary micropolar fluid with boundary data in L2
AbstractWe consider the Dirichlet boundary value problem for the equations of a stationary micropolar fluid in a bounded three-dimensional domain. We show the existence and uniqueness of a distributional solution with boundary values in L2
NMR in the epoxidation of (E,E)-Cinnamylideneacetophenones
The epoxidation of cinnamylideneacetophenones
have been already performed with hydrogen
peroxide as an oxidant in Julia's method [1] and with dimethyldioxirane [2], however no studies were
performed using salen Mn(III) complexes as
catalysts.The epoxidation of cinnatnylideneacetophenones have been already performed with
hydrogen peroxide as oxidant in Julia's method [1] and with dimethyldioxirane [2],
however no studies were performed using salen Mn(lll) complexes as catalysts. On these
basis, we developed a study on the epoxidation of cinnamylideneacetophenones 1,
catalyzed by coinmercially available Jacobsen's catalyst [salen Mn(IIl)] and using
iodosy I benzene and hydrogen peroxide as oxidants. The structure of the epoxidation
products 2-5, their stereochemistry and the regiochemistry of the monoepoxides 2
fotmation were established by ID and 2D NMR spectroscopy. These studies will be
presented and discussed
A comprehensive review on xanthone derivatives as α-glucosidase inhibitors
α-Glucosidase plays an important role in carbohydrate metabolism and is therefore an attractive therapeutic target for the treatment of diabetes, obesity and other related complications. In the last two decades, considerable interest has been given to natural and synthetic xanthone derivatives in this field of research. Herein, a comprehensive review of the literature on xanthones as inhibitors of α-glucosidase activity, their mechanism of action, experimental procedures and structure-activity relationships have been reviewed for more than 280 analogs. With this overview we intend to motivate and challenge researchers (e.g. chemistry, biology, pharmaceutical and medicinal areas) for the design of novel xanthones as multipotent drugs and exploit the properties of this class of compounds in the management of diabetic complications.This work received financial support from the European Union
(FEDER funds POCI/01/0145/FEDER/007265) and National Funds
(FCT/MEC, Fundação para a Ciência e Tecnologia and Ministério da
Educação e Ciência) under the Partnership Agreement PT2020 UID/QUI/50006/2013; FCT UID/QUI/00062/2013, and “Programa Operacional
Competitividade e Internacionalização” (COMPETE) (POCI-
01-0145-FEDER-029241), and under the framework of QREN
(NORTE-01-0145-FEDER-000024). Thanks are also due to Faculdade
de Farmácia da Universidade do Porto and Instituto Politécnico
de Bragança.info:eu-repo/semantics/publishedVersio
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