Taming hazardous chemistry by continuous flow technology.

Over the last two decades, flow technologies have become increasingly popular in the field of organic chemistry, offering solutions for engineering and/or chemical problems. Flow reactors enhance the mass and heat transfer, resulting in rapid reaction mixing, and enable a precise control over the reaction parameters, increasing the overall process selectivity, efficiency and safety. These features allow chemists to tackle unexploited challenges in their work, with the ultimate objective making chemistry more accessible for laboratory and industrial applications, avoiding the need to store and handle toxic, reactive and explosive reagents. This review covers some of the latest and most relevant developments in the field of continuous flow chemistry with the focus on hazardous reactions.

Evaluation of the transfection efficacies of quaternary ammonium salts prepared from sophorolipids.

Five quaternary ammonium amphiphilic compounds were synthesized from sophorolipid 1. These compounds were formulated in aqueous media and some of them (5 and 6) produced well-defined supramolecular aggregates which were characterized by DLS and zeta measurements. Their capacity to transfect four different eukaryotic cell lines in vitro was assessed. To evaluate the influence of the carbohydrate head group from the sophorolipids on the transfection efficacies, their deglycosylated analogues were also synthesized and tested for gene delivery. For all the compounds, the use of DOPE as a helper lipid in a 1 : 1 molar ratio with the ammonium-based lipids was required to obtain homogeneous formulations. The transfection results indicate that quaternary ammonium-based sophorolipids proved to be more efficient pDNA carriers than their deglycosylated counterparts. Moreover, the presence of the carbohydrate head group clearly contributed to the good biocompatibility of these cationic lipids. These cationic sophorolipid derivatives thus offer good potential for the development of new vectors for gene delivery based on renewable resources.

Beyond the Diketopiperazine Family with Alternatively Bridged Brevianamide F Analogues.

A method for the preparation of 3,5-bridged piperazin-2-ones from a tryptophan-proline-based diketopiperazine is described using diphosgene to induce the ring closure. Density functional theory calculations were conducted to study the mechanism of this C-C bond formation. Several derivatives of the thus obtained α-chloroamine were synthesized by substitution of the chlorine atom using a range of O-, N-, S-, and C-nucleophiles. This novel class of brevianamide F analogues possess interesting breast cancer resistance protein inhibitory activity.

Phosphonamide pyrabactin analogues as abscisic acid agonists.

A four step synthesis towards novel phosphonic pyrabactin analogues is presented. Via a stomatal closure and germination assay, the ability of the analogues to selectively induce the ABA-signaling pathway was demonstrated.

Stabilization of emulsions using polymeric surfactants based on inulin.

The use of polymeric surfactants for stabilization of emulsions is described. A brief account of general classification and description of polymeric surfactants is given. This is followed by a description of the adsorption and conformation of polymeric surfactants at interfaces. The theoretical approaches for studying polymer adsorption are briefly described. This is followed by a section on the experimental techniques that can be applied to study adsorption and conformation of polymers at the interface. Examples are given to illustrate the experimental techniques. A section is devoted to the interaction between droplets containing adsorbed polymer layers (steric stabilization). The last section gives results on oil-in-water (O/W) emulsions stabilised with a novel graft copolymeric surfactant based on inulin that has been modified by introducing alkyl groups. Two oils were used, namely Isopar M (isoparaffinic oil) and cyclomethicone. Emulsions prepared using the inulin-based surfactant have large droplets, but this could be significantly reduced by addition of a cosurfactant in the oil phase, namely Span 20. The stability of the emulsions was investigated in water, in 0.5, 1.0, 1.5 and 2 mol dm(-3) NaCl and in 0.5, 1.0, 1.5 and 2 mol dm(-3) MgSO(4). These emulsions were stable for more than 1 year up to 50 degrees C in NaCl concentrations up to 2 mol dm(-3) and 1 mol dm(-3) MgSO(4). This high stability in high electrolyte concentrations could be attributed to the nature of the hydrophilic (stabilizing) polyfructose chain. This was confirmed using cloud point measurements, which showed high hydration of the polyfructose chain in such high electrolyte concentrations. This ensured the long-term physical stability resulting from the strong steric repulsion between the polyfructose chains.

Assessment of the antineoplastic potential of chalcones in animal models.

One part of chemical space that is endowed with interesting biological properties is the area of the chalcones. With this review, we provide a comprehensive overview of the numerous in vivo animal studies on the antineoplastic potential of both natural and synthetic members of this flavonoid subclass (covering: up to mid-2011). The thus far identified modes of action of these compounds are also discussed. We hope that this overview may stimulate deeper investigations into the biochemical mechanisms by which chalcones exert their antineoplastic action. As a result, in the foreseeable future, chalcones may prove suitable lead molecules or early drug candidates for the prevention or treatment of various neoplastic diseases.

Plant polyphenolics as anti-invasive cancer agents.

Because invasion is, either directly or via metastasis formation, the main cause of death in cancer patients, development of efficient anti-invasive agents is an important research challenge. We have established a screening program for potentially anti-invasive compounds. The assay is based on organotypic confronting cultures between human invasive cancer cells and a fragment of normal tissue in three dimensions. Anti-invasive agents appeared to be heterogeneous with regard to their chemical nature, but plant alkaloids, polyphenolics and some of their synthetic congeners were well represented. Even within this group, active compounds were quite diverse: (+)-catechin, tangeretin, xanthohumol and other prenylated chalcones, 3,7-dimethoxyflavone, a pyrazole derivative, an isoxazolylcoumarin and a prenylated desoxybenzoin. The data gathered in this system are now applied in two projects. Firstly, structure-activity relationships are explored with computer models using an artificial neural network approach, based on quantitative structural descriptors. The aim of this study is the prediction and design of optimally efficient anti-invasive compounds. Secondly, the metabolism of orally ingested plant polyphenolics by colonic bacteria is studied in a simulator of the human intestinal microbial ecosystem (SHIME) and in human intervention trials. This method should provide information on the final bioavailability of the active compounds in the human body, with regard to microbial metabolism, and the feasibility of designing pre- or probiotics that increase the generation of active principles for absorption in the gastro-intestinal tract. The final and global aim of all these studies is to predict, synthesize and apply in vivo molecules with an optimal anti-invasive, and hence an anti-metastatic activity against cancer.

Facilitated synthesis of inulin esters by transesterification.

Inulin, the polydisperse polyfructose, extracted from chicory, has been modified via transesterification, using fatty acid methyl esters (FAME). The grafting of an alkyl chain onto the inulin backbone under different conditions for the development of potential tensio-active derivatives is described. The modification of the biopolymer was performed in polar organic solvents, such as dimethyl sulfoxide (DMSO) and N-methylpyrrolidinone (NMP). Depending on the type of solvent, different catalytic systems, such as DMSO-Na+, NaH, and NaOMe, were used and compared in reaction efficiency and reproducibility. Therefore the synthesized derivatives were characterized by 1H- and 13C NMR. The methods using NaH had a mean reaction efficiency of 80%, whereas the one using NaOMe showed a slight decrease in reaction efficiency to 75%. However, the method using NaOMe in NMP proved to be the preferred way to graft the inulin backbone with FAME on a bigger scale. The methods using DMSO as a solvent were not attractive since the end products had a specific bad smell.

Chemical modification of inulin, a valuable renewable resource, and its industrial applications.

Inulin, the polydisperse reserve polyfructose from plants such as Cichorium intybus (chicory), has been chemically modified in several ways to obtain industrially important biodegradable compounds. This review provides an insight on the different types of modification (neutral, anionic, and cationic modification as well as cross-linking and slow release applications) and describes its differences from starch and cellulose chemistry. It also highlights the applications of various compounds cited in the literature.

Polymeric surfactants based on inulin, a polysaccharide extracted from chicory. 1. Synthesis and interfacial properties.

Inulin, the polydisperse reserve polysaccharide from chicory, has been modified by carbamoylation in organic solvents. The reaction of inulin with a range of alkyl isocyanates resulted, after crystalization, in a variety of carbamoylated inulins from which the interfacial properties were determined. The medium and long chain carbamoylated inulins showed a good to very good reduction of the interfacial tension which makes these biopolymers interesting in the field of biodegradable surface active agents.