Química exploratória para o desenvolvimento de novos agentes antimicrobianos a partir de açúcares

Tese de mestrado em Química (Química, Saúde e Nutrição), apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2012In this work new methodologies were developed for the synthesis of new alkyl deoxyglycosides and a new approach was established and validated for the preparation of precursors for the bicyclic sugar moiety of Miharamicyns and analogues. The alkyl deoxyglycosides embodying a chain containing an amide functionality were obtained staring from 22 e 23 in a one-pot reaction that involves three steps with total yields of 11% and 10%, for compounds 27 and 28. For the Miharamicyns precursors and analogues, the overall synthetic pathway was based on sugar regioselective protection, oxidation, Wittig olefination and osmilation, to give branched-chain compounds that will be further transformed into a cyclic lactone which reduction will afford the tetrahydrofuran ring fused to the sugar moiety. This pathway was applied to sugars with various protecting groups starting with glucose and galactose. In addition the reaction conditions used in this synthetic pathway were investigated in order to improve product yields. One of the reactions consisted of the benzylidene formation step, in which the yield could be enhanced of 20%, and the other the oxidation step, where the yield was enhanced up to 70%, when compared to the yields obtained for similar reactions under different conditions. This new approach involving simple, regio- and stereoselective reactions and conveniently protected sugars was developed in order to control reaction outcome of the Wittig step. With the appropriate choice of solvent and protecting groups it was possible to control the regio- and stereoselectivity of this step. Osmilation also took place stereoselectively to give the expected diol precursors of the miharamycins sugar moiety in high yield.Este trabalho teve dois objectivos principais, consistindo um deles na síntese de novos desoxiglicósidos de alquilo para a posterior investigação da sua actividade biológica e toxicidade. O outro objectivo baseou-se na síntese de percursores para a unidade bicíclica das Mi-haramicinas e análogos, tendo o trabalho desenvolvido resultado em novas metodologias para a síntese destes compostos e na preparação de novas entidades moleculares com potencial aplicação como agentes antimicrobianos. Os desoxiglicósidos de alquilo foram sintetizados a partir de 22 e 23 num procedimento que envolveu três passos com rendimentos globais de 11% e 10% para os derivados 27 e 28. Para os precursores das mi-haramicinas, a via sintética envolve vários passos, nomeadamente protecção regioselectiva, oxidação, reacção de Wittig e osmilação, de modo a se obterem açúcares de cadeia ramificada que serão posteriormente transformados numa lactona cíclica que após redução resulta no anel de tetrahidrofurano fundido à unidade sacarídica. Esta estratégia foi aplicada a açúcares com diferentes grupos protectores partido da glucose e galactose. Foram ainda investigadas diferentes metodologias em determinados passos de modo a melhorar rendimentos. Um desses passos consiste na formação do acetal benzilideno, em que o rendimento foi melhorado cerca de 20%, sendo o outro o passo da oxidação, onde houve melhorias na ordem dos 70%, quando comparados aos rendimentos obtidos para reacções semelhantes sob diferentes condições. Foi desenvolvida uma nova metodologia à base de reacções simples, regio- e estereoselectivas com açúcares devidamente protegidos, de modo a controlar o resultado obtido na reacção de Wittig. Com a escolha apropriada do solvente e dos grupos protectores é possível defenir a regio e estereoselectividade deste passo. A osmilação foi feita estereoselectivamente resultando no diol esperado, precursor da unidade sacarídica das mi-haramicinas em bons rendimentos

Erylusamides: Novel Atypical Glycolipids from Erylus cf. deficiens

Among marine organisms, sponges are the richest sources of pharmacologically-active compounds. Stemming from a previous lead discovery program that gathered a comprehensive library of organic extracts of marine sponges from the off-shore region of Portugal, crude extracts of Erylus cf. deficiens collected in the Gorringe Bank (Atlantic Ocean) were tested in the innovative high throughput screening (HTS) assay for inhibitors of indoleamine 2,3-dioxygenase (IDO) and showed activity. Bioassay guided fractionation of the dichloromethane extract led to the isolation of four new glycolipids, named erylusamide A–D. The structures of the isolated compounds were established by 1D and 2D nuclear magnetic resonance (NMR) spectroscopy, high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) and chemical derivatization. The metabolites shared a pentasaccharide moiety constituted by unusual highly acetylated ᴅ-glucose moieties as well as ᴅ-xylose and ᴅ-galactose. The aglycones were unprecedented long chain dihydroxyketo amides. Erylusamides A, B and D differ in the length of the hydrocarbon chain, while erylusamide C is a structural isomer of erylusamide B

Binding and transport properties of a benzo[b]thiophene-based mono-(thio)urea library

Using the chemical versatility of the benzo[ b ]thiophene motif, an extensive library of 24 (thio)urea receptors, with different binding properties and lipophilicities was prepared and included α,α-, α,β-, β,β-, β,γ-, α,γ-, and γ,γ-benzo[ b ]thiophene positional isomers, as well as β- or γ-benzo[ b ]thiophene-based molecules decorated with aliphatic chains or aryl moieties with different fluorination degrees. 1 H NMR titrations, X-ray crystallography studies, and DFT calculations showed that the receptors with higher chloride binding affinities were the β,β- and γ,γ-bis-benzo[ b ]thiophene and fluorinated aryl β- or γ-benzo[ b ]thiophene derivatives that synergistically bind chloride with the urea and one or two C β/γ -H ancillary binding groups. Experimental efflux studies showed that, among these small drug-like molecules, only the highly fluorinated analogues displayed anion transmembrane transport activity, suggesting that this property is dependent on the receptors' lipophilicity and hydrogen bonding ability. Moreover, LUV based assays, undertaken under electroneutral and electrogenic conditions, together with NMDG-Cl assays, indicated that anion efflux occurs mainly through an uniport mechanism. Further MD simulations showed that anion transport is highly dependent on the orientation and interactions of the receptors at the water/lipid interface

Exploring Mannosylpurines as Copper Chelators and Cholinesterase Inhibitors with Potential for Alzheimer’s Disease

Alzheimer’s Disease (AD) is characterized by a progressive cholinergic neurotransmission imbalance, with a decrease of acetylcholinesterase (AChE) activity followed by a significant increase of butyrylcholinesterase (BChE) in the later AD stages. BChE activity is also crucial for the development of Aβ plaques, the main hallmarks of this pathology. Moreover, systemic copper dyshomeostasis alters neurotransmission leading to AD. In the search for structures targeting both events, a set of novel 6-benzamide purine nucleosides was synthesized, differing in glycone configuration and N7/N9 linkage to the purine. Their AChE/BChE inhibitory activity and metal ion chelating properties were evaluated. Selectivity for human BChE inhibition required N9-linked 6-deoxy-α-d-mannosylpurine structure, while all three tested β-d-derivatives appeared as non-selective inhibitors. The N9-linked l-nucleosides were cholinesterase inhibitors except the one embodying either the acetylated sugar or the N-benzyl-protected nucleobase. These findings highlight that sugar-enriched molecular entities can tune bioactivity and selectivity against cholinesterases. In addition, selective copper chelating properties over zinc, aluminum, and iron were found for the benzyl and acetyl-protected 6-deoxy-α-l-mannosyl N9-linked purine nucleosides. Computational studies highlight molecular conformations and the chelating molecular site. The first dual target compounds were disclosed with the perspective of generating drug candidates by improving water solubility

Wittig Reaction: Domino Olefination and Stereoselectivity DFT Study. Synthesis of the Miharamycins’ Bicyclic Sugar Moiety

2-<i>O</i>-Acyl protected-d-<i>ribo</i>-3-uloses reacted with [(ethoxycarbonyl)­methylene]­triphenylphosphorane in acetonitrile to afford regio- and stereoselectively 2-(<i>Z</i>)-alkenes in 10–60 min under microwave irradiation. This domino reaction is proposed to proceed via tautomerization of 3-ulose to enol, acyl migration, tautomerization to the 3-<i>O</i>-acyl-2-ulose, and Wittig reaction. Alternatively, in chloroform, regioselective 3-olefination of 2-<i>O</i>-pivaloyl-3-uloses gave (<i>E</i>)-alkenes, key precursors for the miharamycins’ bicyclic sugar moiety