Enantioselective total syntheses of ropivacaine and its analogues

An alternative asymmetric synthesis of ropivacaine and analogues employing the ‘cation pool’ strategy and host/guest supramolecular co-catalysis approach is presented. In this study, chiral auxiliaries, several soft nucleophiles as well as one-pot conditions for anodic oxidation, followed by nucleophilic addition, have been applied.     

An unusual substitution reaction directed by an intramolecular re-arrangement

Secondary amines and thiols undertake a substitution reaction on the side chain of 2-bromoethyl-pyridinium derivatives ‘directed’ by an intramolecular re-arrangement. Experimental investigations strongly indicate that the reaction is initiated by an alpha addition of the nucleophile onto the iminium moiety of the N-heteroaromatic cation, followed by a cyclisation and an oxidative ring opening. This novel substitution process is able to occur with less reactive nucleophiles that would not undergo conventional substitution with ‘isolated’ bromoethyl moieties.     

A new symmetrically modified α-cyclodextrin tripode: selective metal complexation and fluorescence properties

A new tripodal α-cyclodextrin having three ureido-bipyridyl tethers symmetrically distributed on its upper rim was prepared in one step by the polymer supported ‘phosphine imide’ reaction in a medium yield. As expected, the highly selective complexation properties towards ‘hard’ and ‘soft’ cations were maintained with regards to the URFT-Cd (upper rim fully tethered) family previously investigated. Its Eu^III and Tb^III lanthanide complex fluorescence behaviour clearly indicates that a limited number of tethers allow a better bis-heterocyclic antenna self-organisation around the cation leading to enhanced fluorescence properties.     

Isolation and structural analysis of novel conformational isomers of the m-xylylene-bridged calix[6]arenes: the ‘partial cone’ and ‘inverted cone’ isomers

In the benzylation of a m-xylylene-bridged calix[6]arene tetrol, the first example of the ‘partial cone’ isomer of a calix[6]arene was obtained in addition to the corresponding cone and 1,2,3-alternate isomers, and its structure was established by X-ray crystallographic analysis. The synthesis and crystal structure of the ‘inverted cone’ isomer as well as its thermal conversion to the ‘normal cone’ isomer are also described.     

Quantification of the pore size distribution (porosity profiles) in microfiltration membranes by SEM,TEM and computer image analysis

Transport properties of membranes are closely related to morphological properties like surface porosity and variation of their inner pore structure. Scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM) are powerful tools to characterise the microscopical pore structure of membranes in a qualitative manner. In order to provide more quantitative data of surface and cross-sectional pores computer image analysis can be used. Parameters like ‘porous area fraction’ and ‘mean free path length’ have been selected to describe the pore distribution within porosity profiles in order to consider the effect that the pores within the cross-section are connected to each other.     

The hybrid experimental simplex algorithm – An alternative method for ‘sweet spot’ identification in early bioprocess development: Case studies in ion exchange chromatography

The capacity to locate efficiently a subset of experimental conditions necessary for the identification of an operating envelope is a key objective in many studies. We have shown previously how this can be performed by using the simplex algorithm and this paper now extends the approach by augmenting the established simplex method to form a novel hybrid experimental simplex algorithm (HESA) for identifying ‘sweet spots’ during scouting development studies. The paper describes the new algorithm and illustrates its use in two bioprocessing case studies conducted in a 96-well filter plate format. The first investigates the effect of pH and salt concentration on the binding of green fluorescent protein, isolated from Escherichia coli homogenate, to a weak anion exchange resin and the second examines the impact of salt concentration, pH and initial feed concentration upon the binding capacities of a FAb′, isolated from E. coli lysate, to a strong cation exchange resin. Compared with the established algorithm, HESA was better at delivering valuable information regarding the size, shape and location of operating ‘sweet spots’ that could then be further investigated and optimized with follow up studies. To test how favorably these features of HESA compared with conventional DoE (design of experiments) methods, HESA results were also compared with approaches including response surface modeling experimental designs. The results show that HESA can return ‘sweet spots’ that are equivalently or better defined than those obtained from DoE approaches. At the same time the deployment of HESA to identify bioprocess-relevant operating boundaries was accompanied by comparable experimental costs to those of DoE methods. HESA is therefore a viable and valuable alternative route for identifying ‘sweet spots’ during scouting studies in bioprocess development.     

PHOTOPHYSICAL PROBES FOR MONITORING THE ELECTRIC FIELD/MICROPOLARITY WITHIN THE FAUJASITE SUPERCAGE*

The micropolariry of the supercages of zeolites is a reflection of the electric field provided by the cations present within them. The notion of polarity within the cages of X and Y zeolite does not have precisely the same meaning as in solution. In this study, pyrene, pyrenealdehyde, and para-dimethylaminobenzonitrile have been used as photophysical probes to monitor the polarity of the zeolite interior. With pyrenealdehyde and para-dimethylaminobenzonitrile the supercage wherein the probe is expected to reside is more polar or possesses a higher electric field when the cation is Li or Na. The polarity/electric field of the supercage decreases with cation size (Li > Na > K > Rb > Cs) and the supercage is more polar in the case of X zeolites than in Y zeolites. The results with pyrene are generally consistent with those with the other two probes. However, pyrene is unable to sense the difference between Li. Na and other cations.     

NF-31 color test uncovers ‘hidden’ alcohol functionalities in PEG-based resins for solid phase peptide synthesis

Recently developed PEG-based resins have been shown to markedly improve the quality of the synthesis in case of the so-called ‘difficult’ peptide sequences. Difficult coupling reactions further require sensitive color tests for amines in the assessment of the completeness of coupling. We here describe how the use of PEG-based resins in combination with one of the more sensitive color tests in SPPS can lead to severe misinterpretation and unnecessary delays during solid phase peptide synthesis due to the presence of ‘non-declared’ free hydroxyl functionalities in aminomethyl-PEG-based resins.     

Ship-in-a-bottle synthesis of triphenylamine inside faujasite supercages and generation of the triphenylamminium radical ion

The ship-in-a-bottle synthesis of triphenylamine encapsulated within basic X zeolite has been accomplished by reacting sodium diphenylamide with bromobenzene in the presence of a bifunctional palladium (Hartwig-Buchwald conditions). The presence of incarcerated triphenylamine was demonstrated by dissolving the zeolite with concentrated HF and analyzing the organic material in the dichloromethane extract. Laser flash photolysis (266 nm) gives rise to the generation of triphenylamminium radical cation detected as a transient species decaying in hundreds of microseconds. Upon repetitive cyclic voltammograms, zeolite encapsulated triphenylamine shows a reversible oxidation-reduction process. In contrast, in solution triphenylamine undergoes irreversible oxidation with the formation of coupling dimers.     

Functionalized ionic liquids with highly polar polyhydroxylated appendages and their rapid synthesis via thiol-ene click chemistry

The thiol-ene ‘click’ reaction of 1-thioglycerol with ionic liquids incorporating cations bearing appended vinyl- and/or allyl groups is a versatile, single-step means for their conversion into derivatives bearing up to eight hydroxyl groups per cation.     

Pre-analytical method for NMR-based grape metabolic fingerprinting and chemometrics

Although metabolomics aims at profiling all the metabolites in organisms, data quality is quite dependent on the pre-analytical methods employed. In order to evaluate current methods, different pre-analytical methods were compared and used for the metabolic profiling of grapevine as a model plant. Five grape cultivars from Portugal in combination with chemometrics were analyzed in this study. A common extraction method with deuterated water and methanol was found effective in the case of amino acids, organic acids, and sugars. For secondary metabolites like phenolics, solid phase extraction with C-18 cartridges showed good results. Principal component analysis, in combination with NMR spectroscopy, was applied and showed clear distinction among the cultivars. Primary metabolites such as choline, sucrose, and leucine were found discriminating for ‘Alvarinho’, while elevated levels of alanine, valine, and acetate were found in ‘Arinto’ (white varieties). Among the red cultivars, higher signals for citrate and GABA in ‘Touriga Nacional’, succinate and fumarate in ‘Aragonês’, and malate, ascorbate, fructose and glucose in ‘Trincadeira’, were observed. Based on the phenolic profile, ‘Arinto’ was found with higher levels of phenolics as compared to ‘Alvarinho’. ‘Trincadeira’ showed lowest phenolics content while higher levels of flavonoids and phenylpropanoids were found in ‘Aragonês’ and ‘Touriga Nacional’, respectively. It is shown that the metabolite composition of the extract is highly affected by the extraction procedure and this consideration has to be taken in account for metabolomics studies.     

A study of Heck cyclization reactions to form phenanthridine ring systems

A survey of conditions for the palladium catalyzed intramolecular Heck cyclization of protected amines has shown that the Herrmann-Beller palladacycle can be exploited under ‘cationic’ conditions to provide a robust and rapid route (<2 h) to the synthesis of single double bond isomer phenanthridines in excellent yield (76-99%). In addition, the same cyclization can be performed under ‘neutral’ conditions to provide phenanthridines with a double bond isomer profile suitable for exploitation in diversity-based applications. We have also shown that the highly reactive (^tBu₃P)₂Pd catalyst can induce cyclization at low temperatures (≤50 °C), giving similar results to the ‘neutral’ conditions, and offering an alternative pathway for sensitive substrates.     

Synthesis of imidazolium and pyridinium-based ionic liquids and application of 1-alkyl-3-methylimidazolium salts as pre-catalysts for the benzoin condensation using solvent-free and microwave activation

An efficient one-pot procedure for the synthesis of ionic liquids based on nitrogen-containing heterocycles, imidazolium or pyridinium under ‘green chemistry’ conditions has been described. Imidazolium salts and DBU have been found to catalyze efficiently the benzoin condensation giving good yields within very short reaction time using solvent-free microwave activation conditions.     

Microchip device for rapid screening and fingerprint identification of phenolic pollutants

A new microchip protocol has been developed for rapid measurements of the ‘total’ content of phenolic compounds, as well as for a detailed fingerprint identification of the ‘individual’ ones. The protocol involves the use of a microchip flow-injection analysis for fast screening and early detection of phenols and switching to the separation (fingerprint) mode once such compounds are detected. This is readily accomplished by exchanging the run buffers in the separation channel. While operating with an acidic run buffer (pH 5) offers high speed flow-injection measurements of the ‘total’ phenolic content, on chip switching to a basic buffer (pH 8) leads to ionization of the phenolic compounds and to their effective separation and detection. Under optimum conditions, assay rates of about 120 and 18 samples/h can be realized for the ‘total’ and ‘individual’ measurements, respectively. The effect of the buffer pH, switching (washing) time, applied voltages and other relevant variables, is described. The concept is illustrated in connection to amperometric detection and is attractive for a wide range of environmental-monitoring applications.     

Triazole-linked dendro[60]fullerenes: modular synthesis via a ‘click’ reaction and acidity-dependent self-assembly on the surface

A series of Fréchet-type dendron functionalized [60]fullerene derivatives that bear a 1,2,3-triazole linkage group, referred to as triazole-linked dendro[60]fullerenes, were prepared via a modular synthetic protocol based on a Cu-catalyzed [3+2] cycloaddition (‘click’) reaction. Electronic properties of these dendro[60]fullerenes were investigated by UV-vis spectroscopy and cyclic voltammetry. Interfacial supramolecular self-assembly behavior of these dendro[60]fullerenes was studied using atomic force microscopy (AFM). The resulting self-assemblies showed different nanoscale packing geometries and morphologies on the surface, which are controllable by parameters such as the generation of dendron, the nature of peripheral functionalities, and the experimental conditions (e.g., acidity) applied. Correlations between molecular structure and self-assembling outcome were surveyed and discussed. The results of this study suggest a new avenue to gain better ‘bottom-up’ control over the self-assembly of dendrimer-fullerene hybrid materials in terms of shape and size.     

‘Click chemistry’ in Cu-zeolites: a convenient access to glycoconjugates

Zeolites modified with Cu^I ions are efficient catalyst for ‘click’ reactions involving carbohydrates and aminoacid derivatives. Glycopeptides and oligosaccharides mimics as well as multivalent carbohydrate derivatives have been obtained in good to high yield using heterogeneous Cu^I-modified zeolite catalysts. Contrarily to expectation, pore sizes and internal shapes within zeolites were not a limitation and large glucosyl ditriazoles, disaccharide triazoles, and glucosylated triazolylaminoacids could easily be obtained. Such Cu^I-zeolite heterogeneous catalysts greatly facilitated products recovery, through an easy filtration-solvent evaporation sequence, thus offering a convenient alternative to current methods.     

Unprecedented dual reactivity of anhydrous potassium hydroxide in cascade cyclopropannelation/Haller-Bauer-scission/Grob-fragmentation reactions

We report an unprecedented type of reactivity of ‘anhydrous potassium hydroxide’ (‘APH’) in which it plays, over a large variety of related educts, sequentially the role of base and nucleophile. Some insight into the structure of reactive species as well as comparative reactivity of related reagents prepared by fusion of commercially available potassium hydroxide or by adding stoichiometric amount of water to potassium hydride is provided.     

Synthesis, evaluation and incorporation into liposomes of 4-functionalised-2,5-diphenyloxazole derivatives for application in scintillation proximity assays

The preparation of a series of 4-functionalised-2,5-diphenyloxazoles is described. The scintillating efficiency of each of these ‘scintilipid’ molecules has been evaluated in the presence of ionising radiation. Each ‘scintilipid’ has been assessed for the ability to assemble, with other lipids, into liposomes, under a variety of preparative conditions. Each liposomal preparation has been monitored for the ability to scintillate in the presence of ionising radiation. The optimal ‘scintilipid’, both in terms of effective liposomal formation and scintillation efficiency, has been determined.     

Salt effects on the Baylis-Hillman reaction

The Baylis-Hillman reaction is shown to accelerate in salt solutions of water and the ‘water-like’ structured solvents, like formamide and N-methylformamide in the presence of DABCO. Ethylene glycol, another structured solvent and its salt solutions fail to make any impact on the reaction rates. The salts that are conventionally defined as salting-out or -in do not behave in a similar fashion, when employed in the Baylis-Hillman reactions. The results are supported by solubility measurements. It seems that the cation, anion, nature of solvent and of reactants together ascertain whether a salt will enhance or retard the Baylis-Hillman reaction.     

Reaction of unsymmetrical trifluoromethyl-containing 1,3-dicarbonyl compounds with ‘push-pull’ enamines

The reaction of ‘push-pull’ enamines with trifluoromethyl-containing 1,3-dicarbonyl compounds was investigated. It was found that the reaction is sensitive both to the structure of the enamines and to reaction conditions. As a result, a set of various trifluoromethyldialkylanilines was obtained.