A general synthesis of phosphaalkenes at zirconium with liberation of phosphaformamides.

A general, atom-economical method for the synthesis of phosphaalkenes is reported via the net coupling of primary alkyl or aryl phosphines with aryl or alkyl isocyanides at zirconium. The phosphorus-containing ligand can be liberated as the phosphaformamide from zirconium by reaction with an organic electrophile.

Determination of the endothelin receptor antagonist ABT-627 and related substances by high performance liquid chromatography.

The determination of the endothelin (ET) antagonist receptor ABT-627 (I) and related substances is performed by HPLC. I is determined in bulk drug substance and drug formulation using isocratic conditions and an Inertsil ODS-2 column. The determination is stability indicating and detector response is linear from 24 to 118 microg ml(-1) (33-164% of assay level). Intermediate precision for the determination ranged from +/- 0.60 to +/- 1.9% RSD. The measurement is accurate, with quantitative recovery of I from the formulation placebo. Related substances in I and formulated I are determined using the same chromatographic conditions, with a gradient elution profile to elute impurities having varying relative polarities. The detector response for related substances determination is linear for I from 0.60 to 17.8 microg ml(-1) (0.05-1.5% of assay level) with the limit of detection and quantitation estimated at 0.01 and 0.05%, respectively. Comparable precision was obtained in drug substance and drug formulation (RSD values +/- 3.7 to +/- 12% and +/- 5.5 to 16.9%, respectively for impurities ranging from 0.05 to 0.30%). The quantitated impurities agreed well for the same lot of I when assayed as a bulk substance and after the formulation into a drug product.

Determination of pentobarbital and pentobarbital sodium in bulk drug substance and dosage forms by high-performance liquid chromatography.

High performance liquid chromatography (HPLC) is used to determine impurities in pentobarbital (I) and pentobarbital sodium (II) and to determine the strength of the drug substance and dosage forms. Separations were achieved using a Nucleosil C-18 column (5 microns) measuring 4.6 mm x 15 cm and an eluent containing 0.01 M phosphate buffer at pH 3.5:acetonitrile (72:28). The column is eluted isocratically and UV detection is used at 214 nm. Impurities are determinable in the drug substance at levels > or = 0.01%. Assay precision (relative standard deviations) for impurities in I and II ranged from +/- 36% to +/- 1.3% at levels of 0.01-1.46%. The external standard method is used for quantitating impurities in I and II. The determination of strength in drug substances I and II and in dosage forms (elixir, solution, capsules and suppositories) used the internal standard method. Precision for the strength determination ranged from +/- 0.26 to +/- 1.6%. The accuracy of the procedure was evaluated by addition and recovery of I and II to placebos. Recoveries were quantitative at 50-150% addition levels. Variation in parameters of the separation were made to evaluate the robustness of the HPLC separations.

Determination of 1-benzo[b]thien-2-ylethanone and related impurities by high performance liquid chromatography.

1-Benzo[b]thien-2-ylethanone (2-acetylbenzothiophene, 2-ABT) and related impurities were determined using a reverse-phase high performance liquid chromatography system and UV detection at 254 nm. Separation was achieved isocratically on a 4.6 mm x 25 cm, 5 microns Zorbax Rx-C8 column using an eluent which is 0.2% perchloric acid/THF in a ratio of 60:40 (v/v). The chromatographic system resolved 2-ABT and known impurities in less than 45 min with near baseline resolution. Known impurities were quantitated versus 2-ABT with corrections made for differences in detector response at the specified wavelength. Linearity for 2-ABT was demonstrated with a correlation coefficient > 0.9999. Assay precision (RSD values) for impurities at 0.5% ranged from +/- 1.8% to +/- 14%, while precision (RSD values) for the 2-ABT determination ranged from +/- 0.81% to +/- 1.1%. A variety of different chromatographic columns and conditions are discussed for the application.

Determination of benzalkonium chloride in eye care products by high-performance liquid chromatography and solid-phase extraction or on-line column switching.

Benzalkonium chloride (BAK) is a mixture of alkylbenzyldimethylammonium chlorides, which is commonly used as a bacteriostat. In this work, the three major homologues of BAK are quantitated in the over-the-counter eye care products Murine and Murine Plus using high-performance liquid chromatography (HPLC). The analytes are separated from various product excipients and concentrated by either solid-phase extraction onto Sep-Pak C18 cartridges or by an on-line column-switching technique using 1-cm reversed-phase precolumns. Absolute recoveries of BAK homologues by the solid-phase extraction technique ranged from 97.2 to 98.7% for standards and from 98.0 to 98.4% for samples. Absolute recovery of the BAK homologues by the column-switching technique was 101.3% for standards and ranged from 99.9 to 103.7% for samples. Relative recoveries were quantitative by both techniques. Assay precision (R.S.D. values) were +/- 2.2% to +/- 2.6% and +/- 0.4% to +/- 0.8% by solid-phase extraction and column-switching techniques, respectively. The method provides advantages of high sample throughput, excellent column life and automation.

Determination of cefsulodin, cefmenoxime, and cefadroxil as residues on surfaces.

Cefsulodin, cefmenoxime, and cefadroxil are degraded instantaneously in aqueous sodium hypochlorite, sodium hypochlorite-detergent, or alkaline detergent solutions. These alkaline solutions are used to clean surfaces that have been exposed to the cephalosporins. The cleaned surfaces are monitored for residual drug levels (microgram) using a wet swab-dry swab technique. After extraction from the swabs, the content of the respective cephalosporin is determined in the solution by high-performance liquid chromatography. The limit of detection for each of the compounds is 0.1 microgram/ml. Recoveries from nonporous surfaces ranged from 56 to 102%.

Determination of temafloxacin, sarafloxacin, and difloxacin in bulk drug and dosage forms by high-performance liquid chromatography.

The fluoroquinolones, temafloxacin, sarafloxacin, and difloxacin, are determined in the bulk drug substances and in a variety of dosage form using high-performance liquid chromatography (HPLC). The HPLC system used is also applicable for ciprofloxacin and norfloxacin. The procedure uses UV detection at 280 nm, which provides a linear response of the subject compounds to at least 20 micrograms/ml. Assay precision (RSD) values were +/- 1.2% or better for the bulk drugs and ranged from +/- 0.42 to +/- 2.3% for suspension, capsule, and tablet formulations. Drug recoveries were quantitative from the dosage forms tested. Sensitivity of the subject compounds is approximately 50 ng/ml (2.5 ng on column).

Determination of minor impurities in temafloxacin hydrochloride by high-performance liquid chromatography.

Minor impurities in the antibacterial agent temafloxacin hydrochloride were determined using high-performance liquid chromatography. Manufacturing impurities and degradation products were separated using a reversed-phase system with gradient elution. Detector response was linear for the individual impurities to approximately 50 micrograms/ml which represents 2.5% of the drug concentration. The procedure provides quantitation of impurities to approximately the 0.05% level with precision (relative standard deviations) of 4.7% to 29% in typical bulk drug lots. A variety of reversed-phase columns were evaluated for the assay method with optimum resolution achieved using a 5-microns Nucleosil C18 packing.

Conformational properties of 2,3-methanopyroglutamic acid in peptides: NMR and x-ray diffraction studies.

The effects of replacing L-pyroglutamic acid with the cyclopropane analogue 2,3-methanopyroglutamic acid (2,3-MeGlp) on conformation and enzymatic stability have been investigated in 2,3-MeGlp-NHMe and the novel thyrotropin releasing hormone (TRH) analogue [2,3-MeGlp1]-TRH by x-ray diffraction and nmr. While 2,3-MeGlp-NHMe adopts a folded conformation (small psi angle) in the solid state, several conformations are available to the molecule in solution. 1H-nmr of the diastereomeric mixture [(+/- )-2,3-MeGlp1]-TRH indicates a close orientation of the pyrrolidone and imidazole rings. The 2,3-MeGlp-His amide bond is considerably more stable to pyroglutamate aminopeptidase than the Glp-His bond in TRH.

Determination of spectinomycin dihydrochloride by liquid chromatography with electrochemical detection.

Spectinomycin dihydrochloride is determined by liquid chromatography with electrochemical detection. The drug is chromatographed on a reverse-phase Nucleosil C18 column using an eluent containing 0.02 M sodium citrate and 0.0015 M octyl sodium sulfate (pH 6.10 with perchloric acid) and acetonitrile (100:4). Detection is performed using a coulometric detector (porous carbon working electrode) at +0.85 V. The drug and primary degradation product are detectable. Detector response is linear to at least 20 micrograms/ml, which is four times the assay level. The procedure has relative standard deviations of +/- 1.21 to +/- 2.72% for three lots of bulk drug. Sensitivity is greater than 0.1 microgram/ml of spectinomycin (5 ng on column). Repeatability at this level is +/- 4.94%.

Analysis of oral suspensions containing sulfonamides in combination with erythromycin ethylsuccinate.

The sulfonamides and erythromycin ethylsuccinate in combination oral suspensions were determined by high-performance liquid chromatography and automated turbidimetry, respectively. The chromatographic procedure was rapid, specific, and stability-indicating for sulfisoxazole acetyl and the trisulfapyrimidines using a reversed-phase system with UV detection at 254 nm. Erythromycin ethylsuccinate did not interfere with the sulfonamide analysis and these compounds were assayed with relative standard deviations (RDS) ranging from +/- 2.1 to +/- 3.1%. Erythromycin ethylsuccinate was determined as erythromycin with RSD values of +/- 1.3 or 3.5% without interference by the sulfonamides present.

High-performance liquid chromatographic analysis of clorazepate dipotassium and monopotassium in solid dosage forms.

Methodology for the quantitative determination of clorazepate dipotassium and monopotassium in solid dosage forms was developed. Clorazepate was resolved from its degradation products, making the analysis specific and stability indicating. Analytical separation was performed on a octadecylsilylated silica column. Clorazepate was extracted from the dosage forms with 0.04% NaOH and chromatographed with aqueous 0.005 M tetra-n-butylammonium ion (pH 7.5)- acetonitrile (70:30) as the eluent. The analysis was completed in approximately 20 min with a precision of less than 2.4% RSD.