Reacções de Aza-Diels-Alder dirigidas à síntese de piperidinas polihidroxiladas e tetrahidroquinolinas

Tese doutoramento em Ciências (Área de especialização em Química)Neste trabalho foram obtidos imino-açúcares de seis membros (piperidinas polihidroxiladas), e tetrahidroquinolinas, por reacção de cicloadição [4+2]π de 2H-azirinas/iminas com 1,3-dienos. Para a obtenção das piperidinas polihidroxiladas utilizaram-se duas metodologias diferentes. A primeira abordagem consistiu em fazer reagir 2H-azirinas com furanos e benzofuranos e tratar os aductos com nucleófilos para abrir a ligação epóxido e originar anéis de tetrahidropiridina. No entanto, o tratamento destes aductos com nucleófilos de oxigénio não produziu os resultados esperados. Na maior parte dos casos, o anel de seis membros abriu, gerando compostos do tipo furanólico. Numa segunda abordagem fizeram-se reagir 2H-azirinas com 1,3-butadienos contendo substituintes heterocíclicos na posição 1. Os anéis de seis membros (tetrahidropiridinas) são gerados directamente na reacção de Diels-Alder. Por hidroxilação destes aductos obtiveram-se as estruturas de piperidina polihidroxiladas como era pretendido. Os compostos finais são nucleósidos modificados, já que estrutura de açúcar incorpora uma unidade heterocíclica na posição 1. Obtiveram-se ainda tetrahidroquinolinas fazendo reagir p-metoxifenil glioxalato com diferentes dienófilos electronicamente ricos. Estas reacções são formalmente equivalentes a reacções de Diels-Alder, mas o estudo da estereoquímica de alguns dos compostos obtidos permitiu chegar à conclusão que as reacções ocorriam por um mecanismo não concertado, em dois passos.The aim of this was to obtain six-membered imino-sugars, and tetrahydroquinolines by reaction of 2H-azirines/imines with 1,3-dienes in [4+2]π cycloaddition. Polihydroxylated piperidines were obtained by two different methodologies: 1) reaction of 2H-azirines with furans and benzofurans, followed by treatment of the adducts with oxygen nucleophiles to open the epoxy bridge and obtain tetrahydropiridine intermediates; (expected results were not obtained; the attacking oxygen forces the opening of the six membered ring producing furanolic type compounds in almost all reactions); 2) reactions of 2H-azirines with 1,3-butadienes containing heterocyclic groups at position 1. The six membered tetrahydropiridines were directly generated as products. Hydroxylation of these cycloadducts generated polihydroxylated piperidines as wanted. Final products are modified nucleoside compounds, in which a choosen heterocyclic unit is incorporated at position 1of the sugar sub-structure. Tetrahydroquinolines were obtained by reacting p-methoxyphenyl glioxylate with different electronic-rich dienophiles. The stereochemical study of the products allowed to recognize a non-concerted mechanism in this case

Molecular dynamics simulations together with experimental studies reveal strong membrane activity of a small peptide

251st American Chemical Society National Meeting & Exposition - Computers in ChemistryCell-penetrating peptides (CPPs) and antimicrobial peptides (AMPs) are generally defined as small cationic peptides with the ability to interact with lipidic membranes, in a process driven by electrostatic and hydrophobic processes. The interaction with CPPs is known to lead to its translocation across the membrane, while with AMPs lead to membrane damage. Here we present one synthetic anionic peptide, which strongly interacts with model membranes, showing properties of the two peptide classes, namely the translocation through lipidic membranes on a mechanism usually described for cationic CPPs and membrane destabilization like AMPs promote. These properties were shown through molecular dynamic studies, experimental studies with liposomes and mammalian cells in vitro. Based on the peptide properties here demonstrated, small modifications in its structure could make it a very promising tool for drug delivery.info:eu-repo/semantics/publishedVersio

Hair keratin molecular dynamics studies

EJIBCE 2016 - IV Encontro de Jovens Investigadores de Biologia Computacional EstruturalThe keratin is a key element of the hair, nails and skin in vertebrates. Understand the keratin features such as its assembling in the mentioned structures, its interaction with some compounds or mechanical properties is of great interest in the fight against some diseases or in the development and optimization of cosmetic products. Although molecular dynamics simulations provides unique information at molecular level there are only a few studies using this technique on the study of keratin. This is likely the result of the non-existence of full length keratin crystallographic model. In the few works published about keratin using molecular dynamics simulations the authors had to design and build the computational keratin model, to make the simulations of interest. This work addresses some molecular dynamics studies about hair keratin, from the physicochemical properties of the molecular models to the correlation of the simulations results with experimental data. Our work on this field, with recently developed computational models of hair fibers, is also discussed. We built molecular dynamics models able to reproduce in simulations some phenomena observed in experimental assays, providing important information at molecular level about the mechanisms that lead to the experimental results.info:eu-repo/semantics/publishedVersio

Study of transdermal permeation of large molecules bycoarse-grained molecular dynamics simulation

Skin permeation of large hydrophilic molecules remains a challenge. The barrier function of mammalian skin is mainly attributed to the stratum corneum (SC), the outer protective layer, consisted by flat dead cells filled with keratin and surrounded by lipid bilayers. Within the SC, the lipid bilayers are the major responsible for the skin impermeability to relatively large compounds (molecular weight over 500 Da). The stratum corneum and the skin permeation phenomena can be study by molecular dynamics simulation (MD). Lipid bilayers are studied by MD for a long time, but the most studied ones are cell membranes. There are a few studies on membranes resembling the SC lipids, and even fewer focused on skin permeation. We have developed a membrane model to be identical to the SC lipid bilayers. The composition of the membrane was based in previously reported values for young-normal skin samples and in accordance with previously reported simulations: ceramide-2, lignoceric acid, cholesterol and cholesterol sulphate. This model was used to study skin permeation of large molecular aggregates. The simulations were in accordance with experimental results, and were a valuable tool to understand the mechanism responsible for the transdermal permeation of such large aggregates

Hair keratin molecular dynamics studies

Book of Abstracts of CEB Annual Meeting 2017[Excerpt] The keratin is a key element of the hair, nails and skin in vertebrates. Understand the keratin features such its assembling in the mentioned structures, its interactions with some compounds or mechanical properties is of great interest in the fight against some diseases or in the development and optimization of cosmetic products. Although molecular dynamics (MD) simulations provides unique information at molecular level in a dynamic way, there are only a few studies using this technique on the study of keratin. This is likely the result of the nonexistence of full length keratin crystallographic model. In the few published works the authors had to design and build the computational keratin model to perform the simulations of interest. [...]info:eu-repo/semantics/publishedVersio

Hair keratin molecular dynamics models

251st American Chemical Society National Meeting & Exposition - Computers in ChemistryThe keratin is a key element of the hair, nails and skin in vertebrates. Understand the keratin features such as its assembling in the mentioned structures, its interaction with some compounds or mechanical properties is of great interest in the fight against some diseases or in the development and optimization of cosmetic products. Molecular dynamics modelling is the only technique able to provide information at atomic and molecular level in a dynamic way, which can greatly help in the study of these features. However there are only a few studies using molecular dynamics simulations. This is likely to the non-existence of full length crystallographic structure models of keratin. In the few works published about keratin using molecular dynamics simulations the authors had to design and build the computational keratin model, to make the simulations of interest. This work addresses some keratin models developed, from its physicochemical properties to the correlation of the simulations results with experimental data. Our recently developed computational model of a truncated hair protofibril (8 chains of keratin), which was able to predict the increase of peptide absorption by hair shaft in response to alcohol based formulations, is also discussed.info:eu-repo/semantics/publishedVersio

Keratin molecular dynamics models

The keratin is a key element of the hair, nails and skin in vertebrates. Understand the keratin features such as its assembling in the mentioned structures, its interaction with some compounds or mechanical properties is of great interest in the fight against some diseases or in the development and optimization of cosmetic products. Molecular dynamics modelling is the only technique able to provide information at atomic and molecular level in a dynamic way, which can greatly help in the study of these features. However there are only a few studies using molecular dynamics simulations. This is likely to the non-existence of full length crystallographic structure models of keratin. In the few works published about keratin using molecular dynamics simulations the authors had to design and build the computational keratin model, to make the simulations of interest. This work addresses the different keratin models developed, from its physicochemical properties to the correlation of the simulations results with experimental data. One big computational model of a truncated protofibril (8 chains of keratin), which was able to predict the increase of peptide absorption by hair shaft in response to alcohol based formulations, is also discussed

Tailoring elastase inhibition with synthetic peptides

Chronic wounds are the result of excessive amounts of tissue destructive proteases such as human neutrophil elastase (HNE). The high levels of this enzyme found on those types of wounds inactivate the endogenous inhibitor barrier thus, the search for new HNE inhibitors is required. This work presents two new HNE inhibitor peptides, which were synthesized based on the reactive-site loop of the Bowman–Birk inhibitor protein. The results obtained indicated that these new peptides are competitive inhibitors for HNE and, the inhibitory activity can be modulated by modifications introduced at the N- and C-terminal of the peptides. Furthermore, these peptides were also able to inhibit elastase from a human wound exudate while showing no cytotoxicity against human skin fibroblasts in vitro, greatly supporting their potential application in chronic wound treatment.We would like to acknowledge FCT - Portuguese Foundation for Science and Technology for the scholarship concession; European project Lidwine, contract no. NMP2-CT-2006-026741

Diels–alder reactions of alkyl 2H-azirine-3-carboxylates with furans

Methyl 2-(2,6-dichlorophenyl)-2H-azirine-3-carboxylate 1 and furan give the aziridine 2 by a Diels–Alder cycloaddition reaction. The hydrolysis of compound 2 leads to a dihydrofuranol 11 by cleavage of a C–N bond. X-Ray crystal structures of compounds 2 and 11 have been determined. Compound 2 reacts with alcohols in a similar way to give 2-alkoxy-2,5-dihydrofurans as mixtures of cis and trans isomers. The structures of these compounds have been determined from an X-ray crystal structure of one of the methyl ethers, the trans isomer 13. The reaction of the azirine 1 with 1,3-diphenylisobenzofuran leads to the formation of two isomeric 1 : 1 adducts that have been identified as the products of endo and exo cycloaddition, 3 and 4. The endo isomer 3 is converted into the exo isomer 4 by heat. Similar Diels–Alder reactions have been carried out between furans and benzyl 2H-azirine-3-carboxylate 6. Hydrolysis of the adduct 7 formed with furan again produces a dihydrofuranol 25 as the major product together with three minor products, two of which are 1-azabicyclo[4.1.0]hept-3-ene-2,5-diols 27 and 28 that result from C–O bond cleavage. Protection of the mixture of alcohols with TBS triflate gives the bis(TBS) ether 31 of the trans-1-azabicyclo[4.1.0]hept-3-ene-2,5-diol as the major product, showing that this ring system can be produced from the dihydrofuranol 25. The bis(TBS) ether 30 of the cis-2,5-diol is a minor product and its structure has been established by independent synthesis through a Diels–Alder reaction between the azirine 6 and 1,4-bis(tert-butyldimethylsilyloxy)butadiene 32.Fundação para a Ciência e Tecnologia - POCTI/32723/QUI/2000. FEDER. EPSRC

Gene silencing by siRNA nanoparticles synthesized via sonochemical method

The knowledge that small RNAs can affect gene expression has had a tremendous impact on basic and applied research, and gene silencing is currently one of the most promising new approaches for disease therapy. However, RNAs cannot easily penetrate cell membranes, therefore RNA delivery become one of the major challenges for gene silencing technology. In the current paper we discuss a general approach for converting siRNA molecules into a dense siRNA nanoparticles using environmentally friendly sonochemical method. The RNA nanoparticulation enhance its gene-silencing activity in vascular bovine endothelial as well as in cancer 293T/GFP-Puro cell lines without causing any toxic effect. We show that ultrasonic waves do not lead to RNA degradation or any changes in its chemical structure. Moreover, sonochemically produced siRNA nanoparticles have been shown to be resistant to a variety of environmental stresses including pH levels, enzymes and temperatures, hence solving problem of the short half-life of the RNA molecules. As the siRNA nanoparticles are biocompatibile and biodegradabile, and their RNA release properties may be controlled within limits, sonochemical formation of siRNA nanoparticles represent a new promising approach for generation of functional bionano materials.(undefined