Maria Teresa Barros

Fast Synthesis of N-Acylhydrazones Employing a Microwave Assisted Neat Protocol

A variety of N-acylhydrazones were synthesized under microwave irradiation within 2.5-10 min, starting from benzo, salicyloyl, and isonicotinic hydrazides. The protocol developed employs microwave irradiation in the absence of solvents and catalysts, leading to high yields. The results are reproducible in a 500 mg to 5 g scale.

Polymeric nanoparticles: A study on the preparation variables and characterization methods

Since the emergence of Nanotechnology in the past decades, the development and design of nanomaterials has become an important field of research. An emerging component in this field is nanomedicine, wherein nanoscale materials are being developed for use as imaging agents or for drug delivery applications. Much work is currently focused in the preparation of well-defined nanomaterials in terms of size and shape. These factors play a significantly role in the nanomaterial behavior in vivo. In this context, this review focuses on the toolbox of available methods for the preparation of polymeric nanoparticles. We highlight some recent examples from the literature that demonstrate the influence of the preparation method on the physicochemical characteristics of the nanoparticles. Additionally, in the second part, the characterization methods for this type of nanoparticles are discussed.

Novel Unsaturated Sucrose Ethers and Their Application as Monomers

Novel unsaturated ethers were synthesised in good yields starting from sucrose, using a two-step mild and efficient procedure based on the Gassman method, which consists in forming a vinyl group by the elimination of ethanol from mixed acetals with trimethylsilyl trifluoromethanesulfonate in the presence of alkyl amines. Mixed acetals are readily obtained from the corresponding alcohols and ethyl vinyl ether, using an acidic catalyst. Conventional etherification involving a primary halide was also examined. The monomers thus obtained were successfully polymerised by a free radical mechanism, yielding unbranched linear and soluble polymers with pending sucrose moieties, and some of their physical properties were determined.

Synthesis of Hydrophilic and Amphiphilic Acryl Sucrose Monomers and Their Copolymerisation with Styrene, Methylmethacrylate and α- and β-Pinenes

Herein, we report the synthesis of monomethacryloyl sucrose esters, and their successful free radical homo- and co-polymerisation with styrene, methylmethacrylate, α-and β-pinene. The chemical, physical, structural and surface chemical properties of these polymers, containing a hydrophobic olefin backbone and hydrophilic sugar moieties as side chains, have been investigated. Biodegradation tests of the copolymer samples by a microbial fungal culture (Aspergillus niger) method showed good biodegradability. The chemical structure and surface chemistry of the synthesized homo- and co-polymers demonstrate their potential technological relevance as amphiphilic and biodegradable polymers.

Synthesis and biological evaluation of α-hydroxyalkylphosphonates as new antimicrobial agents

A set of α-quaternary 3-chloro-1-hydroxyalkylphosphonates, analogues of fosfomycin and fosfonochlorin, some of which are new compounds, was synthesized. The compounds were screened for bioactivity against several clinical and standard microbial isolates. Some were found to have moderate activity. The activity was higher with phenyl protection of the phosphoryl ester groups and α-phenyl substitution. Compound 11 was as effective or more potent than fosfomycin or chloramphenicol against several Gram-negative bacteria as well as against some Gram-positive ones.

Sucrose chemistry: Fast and Efficient Microwave-assisted Protocols for the Generation of Sucrose-Containing Monomer Libraries

Sucrose is a carbohydrate feedstock of low molecular weight which is ubiquitous in its availability and is of relatively low cost (Lichtenthaler and Mondel, 1997). The potential value of sucrose as a raw material has been recognized for many years and has been the subject of considerable research. The quest for novel, sustainable, but also structurally robust materials is gaining momentum as the pressure on our environment is building up and the progressive changeover of the chemical industry to renewable feedstock for their raw materials emerges as an inevitable necessity. Although extensive work has been done on the synthesis of glycopolymers, more research efforts are needed to bridge the conceptual, technological and economical gap between fossil hydrocarbons and renewable carbohydrates (Khan, 1984). Sucrose is a particularly appropriate material for use in the formation of many products of commercial significance produced currently from petroleum-based materials, because: it is a naturally occurring, relatively abundant renewable resource; it is polyfunctional, with three reactive primary hydroxyl groups that can be readily and selectively derivatized; it is a 1-2’ linked disaccharide and therefore a nonreducing sugar and thus it does not have the potential for the wide variety of reactions that reducing sugars have; it is a naturally occurring carbohydrate, therefore products based on it are potentially biocompatible and biodegradable (Davis and Fairbanks, 2002). As part of a program directed toward the valorization of sucrose by incorporating it into polymers, its conversion to natural compounds, and its possible application as a chiral auxiliary in selective asymmetric cycloaddition (Lichtenthaler and Peters, 2004), we needed to obtain derivatives of sucrose which could be functionalized easily and selectively at the primary hydroxyl groups (Fig. 1) (Jarosz and Mach, 2002). For this, the development of short and easy routes for the preparation of larger quantities of these target molecules was necessary.

Synthesis of new chiral amines with a cyclic 1,2-diacetal skeleton derived from (2R, 3R)-(+)-tartaric acid.

The syntheses of new chiral cyclic 1,2-diacetals from (2R, 3R)-( )-tartaric acid are described. C(2)-symmetrical diamines were prepared via direct amidation of the tartrate or from the corresponding bismesylate via reaction with sodium azide. For C1-symmetrical compounds, the Appel reaction was used to form the key intermediate, a monochlorocarbinol, from the diol. Some of the new chiral compounds, produced in good to high yields, may be potentially useful as asymmetric organocatalysts or as nitrogen and sulfur chelating ligands for asymmetric metal catalyzed reactions. Thus, a bis-N-methyl-methanamine derivative, used in substoichiometric amounts, was found to catalyze the enantioselective addition of cyclohexanone to (E)-beta-nitrostyrene with high diastereoselectivity (syn / anti = 92:8), albeit giving moderate optical purity (syn: 30 %).

PRE-TREATMENT OF THE PAPER PULP IN THE BLEACHING PROCESS USING BIODEGRADABLE CHELATING AGENTS

The aim of this work was to study the application of two biodegradable chelating agents, pyridine-2,6-dicarboxylic acid (PDA) and methylglycinediacetic acid (MGDA), in the treatment of the pulp, prior to hydrogen peroxide bleaching. Such compounds must remove transition metals (Mn, Fe and Cu) from pulp, that catalyze the degradation of hydrogen peroxide, and Ca, which is also problematic due to the formation of precipitates that accumulate in the equipment. Computer simulations were first performed to study the best conditions for metal complexation, and optimum pH was defined as 5–5.5 for PDA and 6.5–7 for MGDA. Metals removal from the pulp, as well as the subsequent bleaching process (Q-P1-Paa-P2), were tested experimentally, and performances were compared to ethylenediaminetetracetic acid (EDTA). PDA removed both Mn and Ca efficiently, leaving most Mg in the pulp after first chelation stage, while MGDA had a lower Ca removal, even using a higher pH and concentration. Residual hydrogen peroxide and kappa number after peroxide stages showed a similar bleaching efficiency between the studied compounds and EDTA.

Synthesis and antimalarial evaluation of prodrugs of novel fosmidomycin analogues.

The continuous development of drug resistance by Plasmodium falciparum, the agent responsible for the most severe forms of malaria, creates the need for the development of novel drugs to fight this disease. Fosmidomycin is an effective antimalarial and potent antibiotic, known to act by inhibiting the enzyme 1-deoxy-d-xylulose-5-phosphate reductoisomerase (DXR), essential for the synthesis of isoprenoids in eubacteria and plasmodia, but not in humans. In this study, novel constrained cyclic prodrug analogues of fosmidomycin were synthesized. One, in which the hydroxamate function is incorporated into a six-membered ring, was found have higher antimalarial activity than fosmidomycin against the chloroquine and mefloquine resistant P. falciparum Dd2 strain. In addition, it showed very low cytotoxicity against cultured human cells.

Alternative chelating agents: Evaluation of the ready biodegradability and complexation properties

The ready biodegradability of four chelating agents, N,N′-(S,S)-bis[1-carboxy-2-(imidazol-4-yl)ethyl]ethylenediamine (BCIEE), N′-ethylenedi-L-cysteine (EC), N,N′-bis (4-imidazolymethyl)ethylenediamine (EMI) and 2,6-pyridine dicarboxylic acid (PDA), was tested according to the OECD guideline for testing of chemicals. PDA proved to be a readily biodegradable substance. However, none of the other three compounds were degraded during the 28 days of the test. Chemical simulations were performed for the four compounds in order to understand their ability to complex with some metal ions (Ca, Cd, Co, Cu, Fe, Mg, Mn, Ni, Pb, Zn) and discuss possible applications of these chelating agents. Two different conditions were simulated: (i) in the presence of the chelating agent and one metal ion, and (ii) in the simultaneous presence of the chelating agent and all metal ions with an excess of Ca. For those compounds that were revealed not to be readily biodegradable (BCIEE, EC and EMI), applications were evaluated where this property was not fundamental or even not required. Chemical simulations pointed out that possible applications for these chelating agents are: food fortification, food process, fertilizers, biocides, soil remediation and treatment of metal poisoning. Additionally, chemical simulations also predicted that PDA is an efficient chelating agent for Ca incrustations removal, detergents and for pulp metal ions removal process.