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PubMed2003

C4'-spiroalkylated nucleosides having sulfur incorporated at the apex position.

Methodology based on the concept of thionium ion-initiated pinacolic ring expansion has been developed for accessing C4'-spirocyclic thionucleosides. The readily available racemic ketones 6 and 37 are conveniently resolved via their acetals with (R)-mandelic acid. Subsequent reactions beginning with utilization of the Pummerer rearrangement lend themselves to functionalization of the spirocyclic core and ultimately incorporation of the nucleosidic bases. Limitations to this strategy are pointed out. Acquisition of the alpha- and beta-isomers at C4' is equally facile. Absolute configurational assignments have been made possible by X-ray crystallography.

Acetals↗

PubMed1973

The accumulation and metabolism of (-)-noradrenaline by cells in culture.

1. Cultured bovine embryonic tracheal cells, EbTr (NBL-4) possess a process for the intracellular accumulation of (-)-noradrenaline with the characteristics generally ascribed to extraneuronal uptake by cardiac and smooth muscle cells in the body. It has a K(m) of 2.6 x 10(-4)M.2. The accumulation process is inhibited competitively by normetanephrine, but only at relatively high concentrations, IC50=2.1 x 10(-4)M. Inhibition also occurs with 17-beta-oestradiol, IC50=1.3 x 10(-5)M.3. The noradrenaline metabolites, 3,4-dihydroxy-mandelic acid and 3,4-dihydroxy-phenylglycol potentiate accumulation and reduce intracellular levels of normetanephrine in a similar manner to known inhibitors of catechol-O-methyl transferase.4. It is suggested that intracellular, rather than extracellular, normetanephrine may exert feedback inhibition upon noradrenaline accumulation by combining with the transport process at the inner surface of the cell membrane.

Animals↗

PubMed2001

Coupling of simulated moving bed chromatography and fractional crystallisation for efficient enantioseparation.

An optimised coupling of liquid chromatography and fractional crystallisation is suggested for efficient enantioseparation. As a first stage, a chromatographic separation, preferably simulated moving bed (SMB) chromatography, is applied to achieve an enantiomeric enrichment sufficient for a subsequent crystallisation. First results of the experimental and modelling work for the model system (+)-/(-)-mandelic acid in an aqueous solution are described. Chromatographic investigations involve the estimation of adsorption isotherms on a suitable chiral stationary phase and the simulation and optimisation of a corresponding SMB process. From the ternary phase diagram measured for the (+)-/(-)-enantiomer/ solvent system, the conditions required to crystallise a pure enantiomer from an asymmetric mixture can be derived. The productivity gains achievable from the combined process compared to the application of chromatography alone are discussed.

Chromatography, Liquid↗

PubMed1993

Estimation of the number of enantioselective sites of bovine serum albumin using frontal chromatography.

On a column with bovine serum albumin (BSA) immobilized covalently to silica, the adsorption isotherms of the enantiomers of mandelic acid, tryptophan, 2-phenylbutyric acid, and N-benzoylalanine are measured using a buffered mobile phase. Knowing the amount of BSA immobilized on the column (36 mg), the ratio of the number of enantiomer molecules needed to saturate the enantioselective retention mechanism to the number of BSA molecules is determined. The mean of the set of eight enantiomers is 0.28. These data confirm that at most one enantioselective site exists for each BSA molecule for the kind of enantiomers studied.

Adsorption↗

PubMed1978

Arene oxides in styrene metabolism, a new perspective in styrene toxicity?

The metabolism of styrene was studied in the rat after intraperitoneal administration of the cold and the 14C-labeled compound. In addition to phenylethylene glycol, mandelic acid, benzoic acid and hippuric acid, phenolic metabolites, namely, 4-vinylphenol, p-hydroxymandelic acid, p-hydroxybenzoic acid, and p-hydroxyhippuric acid, were identified in the urine of the treated animals. These biotransformation products were characterized by mass spectrometry and by comparative thin layer chromatography with standard compounds. Results of covalent binding studies of 14C-phenylethylene glycol to rat liver microsomal proteins suggest that these phenolic compounds may be formed as a result of chemical rearrangements of unstable arene oxides, reactive intermediates possibly implicated in styrene toxicity.

Animals↗

PubMed1982

Styrene exposure and biologic monitoring in FRP boat production plants.

A survey on styrene exposure was conducted in five small to medium-sized fiber-reinforced plastic (FRP) boat plants utilizing carbon felt dosimeters as personal and stationary samplers to measure 4h (TWA) exposure during workday afternoons. The heaviest exposure, up to 256 ppm by personal sampling and 174 ppm by stationary sampling, took place during the lamination on a mold to produce a boat shell, and the work inside narrow holds also resulted in exposures of a comparable degree. Styrene levels were much lower in other auxiliary works. The TWA of exposure in an entire boat production was estimated to be 40-50 ppm. Installation of several flexible hoses as an exhaust system was proved to be effective in decreasing the vapor concentration. Gas masks were also useful in reducing the exposure. Urine samples were collected from 96 male workers at the end of 8h work (4h in the morning and 4h in the afternoon) and also from 22 nonexposed male subjects, and analyzed for mandelic acid (MA), phenylglyoxylic acid (PhGA), and hippuric acid (HA). When the results of urinalyses were compared with 4-h styrene TWA as monitored by personal sampling, the best correlation was obtained with MA + PhGA/creatinine (the correlation coefficient, 0.88), followed by MA (0.84). For these two cases, regression lines and 95% confidence limits for the group means and for the individual values were calculated. The urinary level of MA, PhGA, and HA in the 22 nonexposed male subjects were also tabulated.

Air Pollutants↗

PubMed1999

Resolution of ephedrine in supercritical CO(2): A novel technique for the separation of chiral drugs.

Racemic ephedrine has been resolved by diastereomeric salt formation with mandelic acid using supercritical CO(2) as precipitating agent. Crystallizations were performed using the Solution Enhanced Dispersion by Supercritical Fluids (SEDS) technique. Temperature was varied between 35 and 75 degrees C, and pressures ranged from 100 to 350 bar. Resolution, determined by chiral capillary electrophoresis, is described as a function of temperature and density of the supercritical fluid. A comparison of SEDS-produced material with a conventional resolution method shows that SEDS-crystallized material exhibits identical properties to conventionally crystallized material.

Carbon Dioxide↗

PubMed2005

Determination of methenamine, methenamine mandelate and methenamine hippurate in pharmaceutical preparations using ion-exchange HPLC.

An ion-exchange column high-performance liquid chromatography (HPLC) method has been developed for the determination of methenamine in methenamine and methenamine hippurate pharmaceutical preparations. The HPLC method uses a Zorbax SCX-300 column with acetonitrile-0.1M sodium perchlorate monohydrate (pH 5.8) (70:30, v/v) as the mobile phase at the flow rate of 1 mL/min. UV-detection was at 212 nm. The linear concentration plots for methenamine were linear over the concentration range of 0.25-50mM for methenamine and methenamine mandelate standards. The intra-day RSD precision was <1.25%, and for inter-day, <1.85%. The peaks for mandelic acid, hippuric acid and the other ingredients from placebo tablets do not interfere with the analysis for methenamine. The accuracy of this method was shown to be 99-101% by measuring the recovery of methenamine from spiked placebo tablets. The assay of methenamine from methenamine hippurate tablets and from a urinary antiseptic tablet containing methenamine were in the range of 98-102%. This HPLC method is a fast, simple and straightforward method for the analysis of methenamine in pharmaceutical preparations.

Anti-Infective Agents, Urinary↗

PubMed2003

Inhibition of mandelate racemase by alpha-fluorobenzylphosphonates.

Mandelate racemase catalyzes the interconversion of the enantiomers of mandelic acid. The enzyme binds the intermediate analogues (R)- and (S)-alpha-fluorobenzylphosphonate, and alpha,alpha-difluorobenzylphosphonate with 100-2500 times less affinity than it exhibits for (R,S)-alpha-hydroxybenzylphosphonate at pH 7.5. This apparent low affinity, relative to that of alpha-hydroxybenzylphosphonate, arises from the altered pKa values of the alpha-fluorobenzylphosphonates. For example, (S)-alpha-fluorobenzylphosphonate is bound with the same affinity as the substrate at pH 7.5, but this affinity is increased approximately 6-fold at pH 6.3.

Benzyl Compounds↗

PubMed1994

Biological monitoring of occupational exposure to electrophilic compounds.

Electrophilic compounds are widely used in industry. Plastic and dyeing industries are foremost examples of sites where workers are exposed to electrophilic compounds. Besides their immediate effect on different body systems, electrophilic compounds include most mutagenic and carcinogenic substances. The present study was carried out to elucidate the possibility of using nonselective assays in the biological monitoring of occupational exposure to electrophilic compounds. The study included a total number of 225 workers selected from the Plastic and Battery Company where workers are exposed to styrene (n = 70), and the Kafr El Dawar chemical and Dyeing Company where workers are exposed to aniline (n = 60) and benzidine (n = 25). Workers exposed to diesel engine exhaust were selected from a bus garage in Smoha (n = 70). A comparison group consisting of 141 subjects was selected from the administrative departments of the selected factories. The biochemical tests carried out on each subject included: (1) estimation of the biological indices of exposure: urinary mandelic acid and benzidine, blood methemoglobin, and carboxyhemoglobin, (2) liver and kidney function tests; and (3) nonselective biochemical parameters of early detection of carcinogenic and mutagenic risk: urinary thioether levels, urinary RNase and alpha esterase activities. The study revealed that two out of three nonselective assays have been affected by occupational exposure to electrophilic compounds. These were the urinary thioethers and RNase levels. Their determination is recommended in the biological monitoring of workers exposed to such agents especially in developing countries.

Adult↗

PubMed1993

Urinary styrene in the biological monitoring of styrene exposure.

The urinary excretion of styrene represents a promising indicator of exposure to this solvent. Nevertheless extensive research under field conditions is scant. In this investigation 214 styrene-exposed workers from 10 fiberglass-reinforced plastics factories were studied. Environmental monitoring was performed by personal passive sampling. Blood styrene and the urinary excretion of styrene and its main metabolites, mandelic acid (MA) and phenylglyoxylic acid (PGA), were measured. The correlation coefficient between the time-weighted average of environmental styrene and the mean urinary excretion of styrene was 0.88 (0.91 after logarithmic transformation), compared with the 0.82 and 0.78 of the end-of-shift MA and PGA values, respectively. A high correlation (0.86) was also found between styrene in the blood and urine. The results, obtained under field conditions with a large group of exposed workers, confirm the usefulness of the urinary excretion of styrene as an exposure index for the biological monitoring of styrene exposure.

Adolescent↗

PubMed2001

Cumulative exposure to styrene and visual functions.

BACKGROUND: Results from a 1990-1992 longitudinal study of several reinforced plastics plants showed that for those workers whose styrene exposure had decreased, color vision (CV) improved; while near visual contrast sensitivity (CS) was poorer. METHODS: In 1999, we retested these visual functions in 18 workers with good visual acuity. A cumulative exposure index (CEI), corrected for respirator use, was calculated for each worker. RESULTS: Intra-individual comparison of mandelic acid (MA) showed a significant decrease over time (Friedman; P = 0.015), but current values were not related to CEI. For CV, no significant difference was observed between 1992 and 1999; present results were not related to MA or CEI. The CS profile decreased over time, with significant differences at 3 cpd (Friedman; P < 0.05). CS did not vary with MA levels, but was significantly depressed at the intermediate frequencies among those in the upper CEIH category (Kruskal-Wallis; P < 0.05). CONCLUSIONS: These findings suggest that CS loss increases with long-term cumulative exposure, reflecting chronic damage to the neuro-optic pathways.

Adult↗

PubMed1981

Ureteric displacement into a silicone cover as protection from an induced retroperitoneal fibrosis: a preliminary report of experiments in rats.

At present, the "therapy of choice" for patients presenting retroperitoneal fibrosis is uretrolysis with intraperitoneal transposition. This procedure, however, leaves the upper and lower part of the ureter vulnerable to recurrent fibrotic stricture since these portions still remain within the retroperitoneal space. In order to protect the ureter in its entire length from aggressive fibrosis an alloplastic cover might offer a better alternative. Following experimental induction of retroperitoneal fibrosis by phenol-mandelic acid in rats the entire ureter was displaced into a silicone envelope. Under the operating microscope the silicone sheath was closed around the renal pedicale by separate sutures of 8-0 prolene. The upper and lateral sealing of this pouch was done by continous sutres and the lower opening of this silicone envelope was fixed to the bladder wall. Progressive retroperitoneal fibrosis caused anterior displacement of the silicone pouch but neither a fibrotic infiltration into this coner nor ureteral stenosis was noted. Histological investigation of these animals in comparison with the control group showed effective protection by the silicone cover. Long-term results of experiments in larger animals well show whether thie procedure might be applied clinically.

Animals↗

PubMed1996

[Mental health deterioration in workers exposed to styrene].

Emotional instability which might be an early symptom of more severe disorders, is one of the first manifestations of chronic exposure to organic solvents. The present study measures the association between exposure to styrene and mood states of active workers. A total of 128 workers (85% of the total population) from 3 factories where styrene is used, participated on a voluntary basis. They filled out the following self-administered questionnaires: Profile of Mood States (POMS), Psychiatric Symptom Index and Well-being Index. The results indicate a significant relationship between post work-shift urinary mandelic acid (biological indicator of styrene exposure) and the scores obtained on the POMS scales of tension-anxiety (Spearman's rank correlation rho = 0.30; p < 0.01), anger-hostility (rho = 0.29; p < 0.01), fatigue-inertie (rho = 0.34; p < 0.01), and confusion-bewilderment (rho = 0.23; p = 0.04), as well as the Psychological Distress Index (rho = 0.30; p < 0.01). All scores were adjusted for the effects of 4 potentially confounding variables: age, schooling, alcohol and cigarette consumption. These indicators of mood states do not constitute a diagnosis of mental disease but reveal progressive deterioration of well being associated with neurotoxic exposure in the workplace.

Adult↗

PubMed1988

Long-term study on workers occupationally exposed to ethylbenzene.

Ethylbenzene is synthesized from benzene; subject to catalytic dehydrogenation it yields styrene, a raw material for the production of synthetic rubber and plastics. Long-term biomonitoring of occupational ethylbenzene exposures, carried out in the past 20 years in some 200 ethylbenzene-production workers, revealed this substance to pose little hazard to human health. As it turned out, mandelic acid concentrations in these workers' urine never exceeded 3.25 mmol.l-1 and none of the exposed showed damage to hematopoiesis and/or liver tissue. Over the last 10 years no case of malignancy has been recorded in this industrial facility belonging to a larger chemical complex where the overall incidence of cancer is about 3 times the national average. Today's low-level ethylbenzene exposures would make it fully justifiable if the present-day MAC limits, both whole-shift (200 mg.m-3) and peak (1,000 mg.m-3), were to be halved, i.e. to be lowered to 100 mg.m3 and 500 mg.m3 respectively. These newly recommended limit values are no more exceeded nowadays.

Air Pollutants, Occupational↗

PubMed1989

Lack of nephrotoxicity of styrene at current TLV level (50 ppm).

Biochemical markers of kidney damage were examined in 37 female workers exposed to an average concentration of 225 mg/m3 of styrene. The concentration of mandelic acid in urine was on the average 759 mg/g creatinine. The mean duration of employment of the exposed subjects was 11 years. The results were compared to those obtained in 35 control female workers matched for age and a number of demographic and lifestyle factors and with no history of exposure to organic solvents. No difference was found in the urinary excretion of albumin, beta 2-microglobulin, retinol-binding protein, total proteins, glucose, lysozyme, lactate dehydrogenase and beta-N-acetyl-D-glucosaminidase. The present study provides thus further evidence that exposure to styrene at the current TLV (215 mg/m3) does not entail any detectable risk for the renal function.

Adult↗

PubMed1984

Exposure-effect and exposure-response relationships between occupational exposure to styrene and neuropsychological functions.

A neuropsychological test battery was administered to 50 workers exposed to styrene and to 50 sex-, intelligence-, and age-matched controls. The main styrene metabolites, ie, mandelic acid (MA) and phenylglyoxylic acid (PGA), were measured as exposure indices in the urine collected on Saturday mornings, just before neuropsychological testing. Exposure-response and exposure-effect relationships were found between the intensity of the exposure (as reflected by the sum of MA and PGA) and the scores of the neuropsychological tests. Verbal learning skills were significantly impaired in workers with a sum of MA and PGA higher than 150 mmole/mole creatinine, corresponding to styrene airborne concentrations higher than 25 ppm (mean daily exposure). Logical memory and visuo-constructive abilities were shown to be significantly affected in workers with MA and PGA higher than 300 mmole/mole creatinine, corresponding to exposure levels of more than 50 ppm of styrene in air.

Adult↗

PubMed1978

Pharmacokinetics of inhaled styrene in rats and humans.

The pharmacokinetic profile of inhaled styrene was examined in rats exposed to levels of 80, 200, 600 or 1,200 ppm for periods of up to 24 h. At levels up to 200 ppm for 6 h, styrene was cleared from the blood according to a two-compartment linear pharmacokinetic model, but at levels of 600 ppm and above the clearance was saturated. In going from 80 to 1,200 ppm (a 15-fold increase), the area under the blood concentration/time curves (AUC) increased by a factor or 112. Fat tissue was shown to comprise the second compartment of the two-compartment pharmacokinetic model. It is suggested that saturation of styrene clearance is due mostly to saturation of the metabolic capacity for styrene. In humans exposed to 80 ppm of styrene for 6 h, styrene was cleared from the blood according to a two-compartment linear pharmacokinetic model similar to that for rats. A maximum blood concentration of 0.9 microgram/ml was reached at the end of the exposure. Most of the inhaled styrene was excreted in the urine as phenylglyoxylic and mandelic acids, and only a small amount as styrene in the expired air. Simulation of the pharmacokinetic model showed that no continued accumulation of styrene would occur during repeated, daily 8-h exposures to 80 ppm. These data reveal that the rat is a reasonable pharmacokinetic model for styrene in humans. At levels of exposure up to 200 ppm, styrene is cleared from the body very efficiently and will not continue to accumulate upon repeated exposure. But at levels of styrene sufficiently high to saturate the metabolic clearance capacity, the integrated dose (measured by the AUC) will be much greater than expected based on exposure levels alone. Therefore, the extrapolation of toxicity observed at high levels of styrene exposure to that expected at low levels may not be justified.

Adipose Tissue↗