Ashraf Ghanem

Separation and sample pre-treatment in bioanalysis using monolithic phases: A review

In order to support drug discovery and development studies within the pharmaceutical industry there has been an increased use of innovative bioanalytical assays and associated analytical technology. Performing quantitative bioanalysis in a variety of biological matrices can also involve the use of sample preparation techniques, complex HLPC column switching and microfluidic systems. Development of assays for diverse therapeutic agents in biomatrices, such as plasma and urine, can be very technically challenging to obtain the sensitivity, speed and specificity required. This challenge focuses on the quantification of drugs and metabolites at very low concentration levels, in an excess of biological matrix and in a high-throughput manner. One area of wide interest is the use and application of monolithic phases where emerging technology has been implemented successfully. This review presents an overview of the application of monolithic phases in a bioanalytical setting, including the bioanalytical challenges that need to be overcome; the synthesis, use and applicability of monolithic phases (with emphasis on polymer-based phases); the currently available bioanalytical techniques and approaches; and future possibilities for these phases.

Chiral separations of piperidine-2,6-dione analogues on Chiralpak IA and Chiralpak IB columns by using HPLC

Recently, two new immobilized polysaccharides based CSPs, namely tris-(3,5-dimethylphenylcarbamate) derivatives of amylose and cellulose known as Chiralpak IA and Chiralpak IB were introduced, which may be used with a wide range of solvents including standard and prohibited ones. Several racemic piperidine-2,6-dione analogues [aminoglutethimide, p-nitro-glutethimide, p-nitro-5-aminoglutethimide, cyclohexylaminoglutethimide, phenglutarimide and thalidomide] have been resolved on Chiralpak IA and Chiralpak IB columns (25cmx0.46cm). The non-conventional mobile phases used were methyl-tert-butyl ether-THF (90:10, v/v) [I], 100% dichloromethane [II] and 100% acetonitrile [III] separately at a flow rate of 1.0mL/min using a UV detector at 254nm. The resolution factors for Chiralpak IA and Chiralpak IB columns were 1.00-5.33 and 0.33-0.67, respectively. Chiralpak IA column gave better results than Chiralpak IB column for the reported molecules using the developed HPLC conditions. Experimental conditions and the possible chiral recognition mechanisms have been discussed.

First x-ray structure of a N -naphthaloyl tethered chiral dirhodium(II) complex: structural basis for tether substitution improving asymmetric control in olefin cyclopropanation

Good-ee! The first one-pot olefin cyclopropanation that gives high ee is reported. The optimized catalyst is the 4-Br-substituted chiral paddle-wheel tetracarboxylatodirhodium(II) complex based on N-naphthaloyl-(S)-tert-leucinate. X-ray structural analysis of the parent catalyst reveals a square chiral crown cavity shrouding the axial coordination site (see figure).

Application and comparison of immobilized and coated amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phases for the enantioselective separation of β-blockers enantiomers by liquid chromatography

A direct liquid chromatographic enantioselective separation of a set of beta-blocker enantiomers on the new immobilized and conventional coated amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phases (Chiralpak IA and Chiralpak AD, respectively) was studied using methanol as mobile phase and ethanolamine as an organic modifier (100:0.1, v/v). The separation, retention and elution order of the enantiomers on both columns under the same conditions were compared. The effect of the immobilization of the amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phase on silica (Chiralpak IA) on the chiral recognition ability was noted when compared to the coated phase (Chiralpak AD) which possesses a higher resolving power than the immobilized one (Chiralpak IA). A few racemates, which were not or poorly resolved on the immobilized Chiralpak IA were most efficiently resolved on the coated Chiralpak AD. However, the immobilized phase withstand solvents like dichloromethane when used as an eluent or as a dissolving agent for the analyte. The versatility of the immobilized Chiralpak IA in monitoring reactions performed in dichloromethane using direct analysis techniques without further purification, workup or removal of dichloromethane was studied on a representative example consisting of the lipase-catalyzed irreversible transesterification of a beta-blocker using either vinyl-acetate or isopropenyl acetate as acyl donor in dichloromethane as organic solvent.

Lipase-catalyzed access to enantiomerically pure (R)- and (S)-trans-4-phenyl-3-butene-2-ol

The enzymatic kinetic resolution of (RS)-trans-4-phenyl-3-butene-2-ol was investigated by screening a range of lipases both for enantioselective transesterification and for enantioselective hydrolysis of its acetate. The lipase from Pseudomonas cepacia immobilized on diatomaceous earth (PSL-D)-catalyzed asymmetric transesterification was performed on gram scale using isopropenyl acetate as an innocuous acyl donor in organic media affording the (S)-alcohol in high enantiomeric excess (>99% ee) and enantiomeric ratio E >150. The lipase (Candida antarctica B, CAL-B)-catalyzed asymmetric hydrolysis of the racemic acetate was performed on gram scale in phosphate buffer affording the (R)-alcohol in high enantiomeric excess (>99% ee) and enantiomeric ratio E >150. The investigation demonstrates that the transesterification of the racemic alcohol in organic solvent was faster than the hydrolysis of the corresponding acetate in phosphate buffer. A GC method was developed to achieve an effective analytical separation of the enantiomers of both substrate and product in one analysis using the chiral stationary phase heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin.

Enantioselective Toxicity and Carcinogenesis

In a non-chiral environment, the enantiomers of a racemate possess the same physico-chemical properties but in the biological systems they possess different activities. One of the enantiomers may be more toxic or carcinogenic, and, therefore, the present data available on the toxicity and carcinogenesis of the racemic mixtures of these chiral pollutants are not reliable and need modification in terms of the enantioselective toxicity and carcinogenesis. It is essential to explore the enantioselective toxicity and carcinogenesis due to the different enantiomers of the chiral pollutants. The knowledge of the stereoselective metabolisms of the chiral pollutants may be useful for the treatment of cancer and other diseases. The enantioselective toxicity and carcinogenesis due to the chiral pesticides, pollutants and some drugs have been discussed in this review article.

Recent advances in silica-based monoliths: Preparations, characterizations and applications†

This mini-review describes recent progress (2009-2010) in the field of silica-based monolith with special emphasis on the preparation, characterization and applications.

Whats New in Chromatographic Enantioseparations

Progress in different areas of enantioselective chromatography and its applications in last years (2002-2003) is reviewed. Special attention is devoted to chromatographic enantioseparations of different drugs and natural compounds

Asymmetric hydrogenation of an α,β-unsaturated ketone by diamine(ether–phosphine)ruthenium(II) complexes and lipase-catalyzed kinetic resolution: a consecutive approach

Abstract The RuCl2(η1-Ph2PCH2CH2OCH3)2(diamine) complexes 2L1–2L5 have been prepared in high yields from the reaction of equimolar amounts of RuCl2(η2-Ph2PCH2CH2OCH3)2 1 with various kinds of chelating diamines L1–L5 to form five-membered chelates with ruthenium. These novel ruthenium(II) complexes have been used as catalysts in the asymmetric hydrogenation of the prochiral ketone trans-4-phenyl-3-butene-2-one 3, using 2-propanol and different types of cocatalysts. Whereas complexes with achiral diamines afforded the racemic alcohols, complexes with chiral diamines (R,R or S,S) allowed the formation of the corresponding enantiomerically enriched secondary alcohol (S or R) with ee values of 45%. In order to obtain the secondary alcohol with ee of >99%, the kinetic resolution of enantiomerically enriched trans-4-phenyl-3-butene-2-ol 3 was performed in a consecutive approach using either the lipase-catalyzed enantioselective transesterification of the alcohol with isopropenyl acetate as the acyl donor in toluene or the enantioselective hydrolysis of the corresponding acetate in buffer. The determination of the enantiomeric excess (ee) of the resulting enantiomerically enriched secondary alcohols was performed by gas chromatography using heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin as the chiral stationary phase.

Current trends in separation of plasmid DNA vaccines: A review

Plasmid DNA (pDNA)-based vaccines offer more rapid avenues for development and production if compared to those of conventional virus-based vaccines. They do not rely on time- or labour-intensive cell culture processes and allow greater flexibility in shipping and storage. Stimulating antibodies and cell-mediated components of the immune system are considered as some of the major advantages associated with the use of pDNA vaccines. This review summarizes the current trends in the purification of pDNA vaccines for practical and analytical applications. Special attention is paid to chromatographic techniques aimed at reducing the steps of final purification, post primary isolation and intermediate recovery, in order to reduce the number of steps necessary to reach a purified end product from the crude plasmid.