Approaches to quantitative structure-enantioselectivity relationship modeling of chiral separations using capillary electrophoresis

Quantitative structure-enantioselectivity relationships (QSERs) have been developed to describe the resolution of a series of chiral arylpropionic acids using capillary electrophoresis. Native beta-cyclodextrin and two derivatized forms are used as the chiral resolving agents. The QSER models are developed using the results of molecular mechanics calculations as input to multivariate linear regression and also to neural networks. Single models are developed to predict the optimum cyclodextrin to resolve a given analyte, the migration order, and the magnitude of the separation. Models are also developed to predict only the optimum cyclodextrin.     

Laser-induced reactions of NO2 in the visible region

The reaction of NO₂ with isobutane, induced by 488 nm laser radiation, to form 2-nitro-2-methylpropane has been investigated and the results computer-modeled according to two possible reaction mechanisms. The first scheme involves the direct abstraction of H from isobutane by vibronically excited NO₂ (NO ₂ ^* ), and the second, abstraction by an intermediate NO₃ radial produced by NO ₂ ^* +NO₂. The modeling results strongly support the NO ₂ ^* scheme as the dominant reaction mechanism.     

Synthesis of the methanesulfonates of α-(4-chlorophenyl)-α-[1-(2-chlorophenyl)emenyl]-1H-1,2,4-triazole-1-ethanol and α-[1-(2-chlorophenyl)ethenyl]-α-(2,4-difluorophenyl)-1H-1,2,4-triazole-1-ethanol,alpha styryl carbinol antifungal agents

The methanesulfonates of (α-(4-chlorophenyl)-α-[1-(2-chlorophenyl)ethenyl]-1H-1,2,4-triazole-1-ethanol and α-[1-(2-chlorophenyl)ethenyl]-α-(2,4-difluorophenyl)-1H-1,2,4-triazole-1-ethanol ( 1a, b ) are orally effective α-styryl carbinol derivatives developed for the treatment and prevention of systemic fungal infections. Practical new processes amenable for the large-scale production of these compounds are described. Of note is the selection of dichlorostyrene as a convenient precursor of the styryl portion, modification of a sensitive Grignard addition into a realistic preparative reaction and the use of 1,2,4-triazole simultaneously as a base transfer agent and nucleophile.     

Lanczos cluster expansion for non-extensive systems

A cluster expansion of the Lanczos recursion for non-extensive systems is developed based on the plaquette expansion for extensive systems, in which an auxiliary scaling parameter, Ω, plays the role of volume and introduces extensivity into the problem. Connected Hamiltonian moments of the non-extensive system are computed and introduced into the plaquette expansion in the usual way with Ω. The extensive energy is calculated for increasing orders of the expansion in 1/Ω and the ground state and mass gap of the finite few body problem recovered in the limit Ω → ∞. This new non-perturbative method is applied to the case of N bosons interacting harmonically in one dimension and the ground state energy and mass gap in the vacuum sector are calculated exactly.     

Ferric-ion-photosensitized damage to DNA by hydroxyl and non-hydroxyl radical mechanisms.

Iron(III) and UVA (320-400 nm) light strongly diminished the transforming activity of Haemophilus influenzae DNA in the presence of oxygen. Iron(III) alone in the absence of light had no measurable effect on the transforming activity. The chelating agent ethylenediaminetetraacetic acid (EDTA) conferred virtually complete protection, but hydroxyl radical scavengers (mannitol, methanol, ethanol, isopropanol and dimethyl sulfoxide) inhibited only a small fraction of the inactivation. Treatment of plasmid DNA (pBR322) with iron(III) results in the conversion of the covalently closed circular form of the plasmid to open circles and ultimately to the linear form. Concomitant with the alteration in the conformation of the plasmid, the ability to transform Escherichia coli was reduced. In model systems, iron(III) photoreacted with the DNA backbone causing nicking and double-strand breakage. The results are consistent with a mechanism involving a preliminary complexation of iron(III) by DNA followed by the generation of reactive free radicals other than .OH. We suggest that bound iron, or other UV-absorbing transition metal complexes, may be chromophores capable of causing DNA damage in the long-wave near-UV region.     

Determination of N-acetylator phenotype using caffeine as a probe compound: a comparison of high-performance liquid chromatography and capillary electrophoresis methods.

A test for determining N-acetylator metabolic phenotype has been developed using caffeine as a probe drug. A spot sample of urine is taken, and the unextracted urine is then analysed by micellar electrokinetic capillary chromatography. Phenotype is determined from the peak-area ratio of urinary 5-acetylamino-6-formylamino-3-methyluracil to 1-methylxanthine. Phenotype assignments using this method were compared with those made using a standard high-performance liquid chromatography assay, with good agreement between the two methods. The advantage of the capillary electrophoresis analysis is that no sample extraction is necessary, resulting in a total analysis time of around 20 min, and removing a potential source of error.     

High-speed gradient parallel liquid chromatography/tandem mass spectrometry with fully automated sample preparation for bioanalysis: 30 seconds per sample from plasma

In this work, a high-throughput and high-performance bioanalytical system is described that is capable of extracting and analyzing 1152 plasma samples within 10 hours. A Zymark track robot system interfaced with a Tecan Genesis liquid handler was used for simultaneous solid-phase extraction of four 96-well plates in a fully automated fashion. The extracted plasma samples were injected onto four parallel monolithic columns for separation via a four-injector autosampler. The use of monolithic columns allowed for fast and well-resolved separations at a considerably higher flow rate without generating significant column backpressure. This resulted in a total chromatographic run cycle time of 2 min on each 4.6 x 100 mm column using gradient elution. The effluent from the four columns was directed to a triple quadrupole mass spectrometer equipped with an indexed four-probe electrospray ionization source (Micromass MUX interface). Hence, sample extraction, separation, and detection were all performed in a four-channel parallel format that resulted in an overall throughput of about 30 s per sample from plasma. The performance of this system was evaluated by extracting and by analyzing twelve 96-well plates (1152) of human plasma samples spiked with oxazepam at different concentrations. The relative standard deviation (RSD) of analyte sensitivity (slope of calibration curve) across the four channels and across the 12 plates was 5.2 and 6.8%, respectively. An average extraction recovery of 77.6% with a RSD of 7.7% and an average matrix effect of 0.95 with a RSD of 5.2% were achieved using these generic extraction and separation conditions. The good separation efficiency provided by this system allowed for rapid method development of an assay quantifying the drug candidate and its close structural analog metabolite. The method was cross-validated with a conventional liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay.     

Surface amplification of invasive cleavage products

A major focus of current efforts in genomics is to elucidate the genetic variations extent within the human population, and to study the effects of these variations upon the human system. The most common type of genetic variations are the single nucleotide polymorphisms (SNPs), which occur every 500-1000 nt in the genome. Large-scale population association studies to study the biological or medical significance of such variations may require the analysis of hundreds of thousands of SNPs on thousands of individuals. We are pursuing development of an approach to large-scale SNP analysis that combines the specificity of invasive cleavage reactions with the parallelism of high density DNA arrays. A surface-immobilized probe oligonucleotide is specifically cleaved in the presence of a complementary target sequence in unamplified human genomic DNA, yielding a 5' phosphate group. High sensitivity detection of this reaction product on the surface is achieved by the use of rolling circle amplification, with an approximate concentration detection limit of 10 fM target DNA. This combination of very specific surface cleavage and highly sensitive surface detection will make possible the rapid and parallel analysis of genetic variations across large populations.