Reply to "Comment on Renormalization group picture of the Lifshitz critical behaviors"

We reply to a recent comment by Diehl and Shpot (cond-mat/0305131) criticizing a new approach to the Lifshitz critical behavior just presented (M. M. Leite Phys. Rev. B 67, 104415(2003)). We show that this approach is free of inconsistencies in the ultraviolet regime. We recall that the orthogonal approximation employed to solve arbitrary loop diagrams worked out at the criticized paper even at three-loop level is consistent with homogeneity for arbitrary loop momenta. We show that the criticism is incorrect.Comment: RevTex, 6 page

Bioclimatic modelling in the holocene and in future warming scenarios in Arbutus unedo L.

Growing forests wildfires in Portugal are an increasing concern since forests in the Mediterranean region are vulnerable to recent global warming. Long-term negative effects are expected on the vegetation with the coming increasing drought. The strawberry tree (Arbutus unedo L.) displays potential to be a successfully business-like cultured in several regions of Portugal and southern Europe, as it is well adapted to climate and soils. In Portugal, this species has been used by local populations particularly for spirit production and for fruit consumption, although it has different possible commercial uses, from processed and fresh fruit production to ornamental, pharmaceutical and chemical applications. In addition, due to its pioneer status, it is valuable for land recovery and desertification avoidance, besides being fire resistant. The available strawberry tree’s data is presence-only. For modelling purposes, a set of placements within the landscape of interest (Portugal) was applied. The species, observed in 318 plots, together with a vector of environmental covariates (7 bioclimatic attributes, slope and altitude) and a defined background were used for modeling purposes. Maxent 3.4.1 was the used software, where the estimated quantity is the probability of the presence of the species, conditioned on the environment. Maxent uses the environmental covariate data from the occurrence records and the background sample, to estimate the ratio between the conditional density of the covariates at the presence sites and the marginal (i.e., unconditional) density of covariates across the study area and so, estimating the relative suitability of one place vs. another. Three different climate scenarios (control run; 2050 and 2070) were tested for two emission scenarios (RCP 4.5 and RCP 8.5, WorldClim), besides the past, 6,000 BP (Mid-Holocene). The reduction of habitat suitable for this species is very significant in the southern regions, even for the best warming scenario (RCP 4.5) in 2050. Central and Northern mountain regions are predicted refuge for this species. Forest policies and management should consider the impact of climate change on the usable areas for forestry, seeing a case-study species particularly adapted to the Mediterranean regions and wildfires, such as strawberry tree. The distribution of the species in the Middle Holocene agrees with previous genetic and fossils studies in the region, which supported two putative refuges for the species since the Last Glacial Maximum and a cryptic refugia in the East-Central mountain region.info:eu-repo/semantics/publishedVersio

Synthesis of 2-{2-[5(4)-aryl-2H-[1,2,3]-triazol-4(5)-yl]vinyl}chromen-4-ones

Chromones are a family of oxygen-containing heterocyclic compounds that have been shown particular relevant biological activity. In what concerns to 2-methylchromones, their reactivity is well-known and allowed to exploit many different kinds of chemical reactions. The acidic character of the 2-methyl group, due to the low electron density at C-2 caused by carbonyl group enable this class of compounds to undergo oxidation, photolysis, cycloaddition and condensation reactionsUniversity of Aveiro, Funda9ao para a Ciencia e Tecnologia (FCT, Portugal), European Union, QREN, FEDER and COMPETE for funding the QOPNA Research Unit (project PEst-C/QUI/UI0062/2011) and the Portuguese National NMR Network. Hello Albuquerque also thanks FCT for his fellowship (SFRH/Bl/51556/2011 )

Nitromethane conjugate addition to 2-[(1E,3E)-4-arylbuta-1,3-dien-1-yl]-4Hchromen- 4-ones

Chromone are a group of oxygen-containing heterocycles, which are often associated to important biological activities.1 Chromone derivatives are also seen as interesting scaffolds to input further functionalizations,2 most of them through chemical transformations such as oxidation, condensation, Diels-Alder or conjugate addition. Conjugate addition of carbon nucleophiles to electron-deficient alkenes is one of the most important methods available for carbon–carbon bond-forming reactions. A wide range of carbon nucleophiles easily undergo conjugate addition with various substrates such as chalcones, cinnamylideneacetophenones or styrylchromones. Following previous work of our research group involving the 1,6-conjugate addition of nitromethane to (E)-2- styrylchromones,3 herein we report the first reactivity studies in the nitromethane conjugate addition to the extended unsaturated π-system of 2-[(1E,3E)-4-arylbuta-1,3-dien-1-yl]-4H-chromen-4-ones 1 (Scheme 1). The DBU catalyzed nitromethane addition reaction afforded the corresponding β-(nitromethyl)chromones 2 (1,6-conjugate addition) as major products. (E)-5'-(Nitromethyl)-3'-styryl-[1,1'-biphenyl]-2-ol 3 and 3'-aryl-2'-nitro-5'-(nitromethyl)spiro [chromane- 2,1'-cyclohexan]-4-one 4 derivatives were also isolated as minor products, which result from the addition of two nitromethane molecules, through tandem processes.info:eu-repo/semantics/publishedVersio

Chalcones as versatile synthons for the synthesis of 5- and 6-membered nitrogen heterocylces

Chalcones belong to the flavonoid family which constitutes one of the major classes of naturally occurring oxygen heterocyclic compounds. The alpha,beta-unsaturated carbonyl system of chalcones possesses two electrophilic reactive centers allowing them to participate in addition reactions via attack to the carbonyl group (1,2-addition) or involving the beta-carbon (1,4-conjugate addition), leading to the synthesis of promising bioactive heterocyclic compounds. The purpose of this review is to present a systematic survey of the most recent literature that uses chalcones in the synthesis of biologically active 5- and 6-membered nitrogen heterocycles such as pyrroles, indoles, isoxazoles, imidazoles, pyrazoles, indazoles, triazoles, tetrazoles, pyridines and pyrimidines. Efficiency, easy-to-handle and cheap reagents, alternative heating conditions and greener protocols will be highlighted. In this review we will cover the literature since the beginning of the 21st century in more than 400 publications.PEst-C/QUI/UI0062/2013 FCOMP-01-0124-FEDER-03729

Cholesterol-based compounds: Recent advances in synthesis and applications

This review reports on the latest developments (since 2014) in the chemistry of cholesterol and its applications in different research fields. These applications range from drug delivery or bioimaging applications to cholesterol-based liquid crystals and gelators. A brief overview of the most recent synthetic procedures to obtain new cholesterol derivatives is also provided, as well as the latest anticancer, antimicrobial, and antioxidant new cholesterol-based derivatives. This review discusses not only the synthetic details of the preparation of new cholesterol derivatives or conjugates, but also gives a short summary concerning the specific application of such compoundsThanks are due to the University of Aveiro, Instituto Politécnico de Bragança, FCT/MEC for financial support of the QOPNA (FCT UID/QUI/00062/2013) and CIMO (UID/AGR/00690/2013) research units, through national funds, and where applicable cofinanced by the FEDER, within the PT2020 Partnership Agreement; and also to the Portuguese NMR Network. This work was also supported by the Integrated Programme of SR&TD “pAGE–Protein aggregation Across the Lifespan” (reference CENTRO-01-0145-FEDER-000003), co-funded by the Centro 2020 program, Portugal 2020, European Union, through the European Regional Development Fund. H. M. T. Albuquerque thanks the pAGE project for his Post-Doc grant (BPD/UI98/4861/2017).info:eu-repo/semantics/publishedVersio

Chromones as versatile building blocks in cycloaddition reactions

4H-Chromen-4-ones commonly referred as chromones are a class of naturally occurring heterocyclic compounds implicated in a series of biological and pharmacological properties.[1] It is also an interesting scaffold involved in a range of chemical transformations for the preparation of novel and more complex oxygen-containing heterocyclic derivatives.[2] Following our interest in the chemistry of chromones, we design two different building blocks, 2- [(1E,3E)-4-arylbuta-1,3-dien-1-yl]-4H-chromen-4-ones 1 and (E)-2-(4-arylbut-1-en-3-yn-1-yl)-4Hchromen- 4-ones 2, and explore the reactivity of the unsaturated systems in cycloaddition reactions. In the former case, chromones 1 were used as dienes in microwave-assisted Diels–Alder (DA) reactions with various electron-poor and electron-rich dienophiles to provide flavone-type compounds 3.[3] In the latter case, the diene system of chromones 2 was involved in DA reactions with N-methylmaleimide whereas the acetylene moiety react with sodium azide, via 1,3-dipolar cycloaddition reaction, to afford xanthene-1,2,3-triazole dyads 4.[4] In this communication, we will present and discuss the synthetic details and spectroscopic characterization of the main products and some interesting byproducts, as well as the intermediate compounds isolated in each case.Thanks are due to University of Aveiro and FCT/MEC for the financial support of the QOPNA research unit (FCT UID/QUI/00062/2013) through national founds and, where applicable, co-financed by the FEDER, within the PT2020 Partnership Agreement, and to the Portuguese NMR Network, as well as to the Instituto Politécnico de Bragança. H.M.T.A. is grateful to FCT for their PhD grant (SFRH/BD/86277/2012).info:eu-repo/semantics/publishedVersio

Synthesis of xanthone-1,2,3-triazole dyads

Xanthones and 1,2,3-triazoles are known to exhibit several biological, pharmacological and biocidal properties[1]. The potential applications of these two classes of heterocycles led us to develop new strategies to synthesize xanthone-1,2,3-triazole dyads, aiming to get potentially improved therapeutic agents[2]. With this rational in mind we designed and synthesized novel chromone derivatives 1a-d to be used as building motifs and to explore the reactivity of the two unsaturated systems (the diene and the alkyne). In the present communication we will present a new synthetic route towards the synthesis of xanthone-1,2,3-triazole dyads 7a-d using consecutively the azide-alkyne Huisgen 1,3-dipolar cycloaddition and Diels-Alder reaction. Our approach involves the synthesis chromone-triazole derivatives 2a-d using the reaction of 1a-d with sodium azide, followed by the methylation of the NH of the triazole moiety. The methylation afforded three isomers 3a-d, 4a-d and 5a-d, as expected. The major isomers 3a-d were used in the Diels-Alder reaction with N-methylmaleimide, and the adducts obtained 6a-d were oxidized to afford the xanthone-1,2,3-triazole dyads 7a-d. All the synthetic details as well as the structural characterization (by 1D and 2D NMR studies) of the new synthesised compounds will be presented and discussed

2-(4-Arylbuta-1,3-dien- or 1-en-3-yn-1-yl)chromones as synthons for the synthesis of other nitrogen and oxygen heterocyclic compounds

It is well known the great biological relevance of oxygen and nitrogen heterocycles. Herein, the reactivity of 2-(4-aryl-1,3-dien- and 1-en-3-yn-1-yl)chromones are explored in order to establish new synthetic routes towards the preparation of new heterocyclic compounds such as xanthones and triazoles. The reactive sites of the starting chromone derivatives (the double and triple bonds) allow them to be involved in reactions such as Diels-Alder and Huisgen cycloadditions. These reactions are used separately or subsequently in order to prepare new biologically active compounds emphasizing the synthetic potential of the referred chromone derivatives. Using these new synthetic routes we were able to develop new compounds, such xanthones bearing triazole moiety, which are expected to enclosure interesting biological properties

Novel chromone and xanthone derivatives: synthesis and ROS/RNS scavenging activities

Chromones and xanthones are oxygen-containing heterocyclic compounds acknowledged by their antioxidant properties. In an effort to develop novel agents with improved activity, a series of compounds belonging to these chemical classes were prepared. Their syntheses involve the condensation of appropriate 2-methyl-4H-chromen-4-ones, obtained via Baker-Venkataraman rearrangement, with (E)-3-(3,4-dimethoxyphenyl)acrylaldehyde to provide the corresponding 2-[(1E,3E)-4-(3,4-dimethoxyphenyl)buta-1,3-dien-1-yl]-4H-chromen-4-ones. Subsequent electrocyclization and oxidation of these compounds led to the synthesis of 1-aryl-9H-xanthen-9-ones. After cleavage of the protecting groups, hydroxylated chromones and xanthones were assessed as scavenging agents against both reactive oxygen species (ROS) [superoxide radical (O2(•-)), hydrogen peroxide (H2O2), hypochlorous acid (HOCl), singlet oxygen ((1)O2), and peroxyl radical (ROO(•))] and reactive nitrogen species (RNS) [nitric oxide ((•)NO) and peroxynitrite anion (ONOO(-))]. Generally, all the tested new hydroxylated chromones and xanthones exhibited scavenger effects dependent on the concentration, with IC50 values found in the micromolar range. Some of them were shown to have improved scavenging activity when compared with previously reported analogues, allowing the inference of preliminary conclusions on the structure-activity relationship