Astrid Michelitsch

Determination of hypericin in herbal medicine products by differential pulse polarography

A differential pulse polarographic method is presented for the determination of total hypericin in phytotherapeutic preparations (drops, tablets and capsules). The polarographic behaviours of hypericin and of pseudohypericin were examined in various buffer systems over the pH range 3.5–10.0. In Britton Robinson buffer:methanol solution (at pH 6.0) the differential pulse polarograms exhibited reproducible peaks at Ep−1.02 V vs silver/silver chloride for hypericin, and at −1.00 V for pseudohypericin. Under these conditions, a plot of peak height against concentration of hypericin was found to be linear over the range 0.5–9.0 µg/mL (r = 0.9994) and 9.0–16.0 µg/mL (r = 0.9987). The polarographic method was applied to the determination of the content of total hypericin (hypericin, pseudohypericin, protohypericin and protopseudohypericin) in herbal medicinal products containing Hypericum perforatum. The precursors protohypericin and protopseudohypericin were converted into hypericin and pseudohypericin, respectively, by subjecting them to artificial light or daylight prior to analysis. Under these conditions, no separation step was required for the polarographic analysis. In order to evaluate the total concentration of hypericin, the standard addition method with hypericin as standard was applied. The relative standard deviation involved in analysing various herbal medicinal products ranged from ±1.9 to 2.9%. Copyright

2H-Isoindol-4,7-dione durch Addition von Azomethinyliden an 1,4-Benzochinone

SummaryA new approach to the synthesis of 2H-isoindole-4,7-diones is described. Heating α-amino acids with carbonyl compounds generates azomethine ylides through the elimination of water and carbon dioxide. The ylides were captured by quinones forming 2H-isoindole-4,7-diones, 2,3,3a,7a-tetrahydro-1H-isoindole-4,7-diones and 2,3-dihydro-1H-pyrrolo[2,1-a]isoindole-6,9-diones. The structures were established on the basis of spectroscopy (NMR, mass).

Elektrochemische Eigenschaften von 6-Methoxy-2,5-dimethyl-2H-isoindol-4,7-dion, einem antimikrobiell wirksamen Alkaloid ausReniera-Arten

SummaryTo determine the electronaffinity of 6-methoxy-2,5-dimethyl-2H-isoindole-4,7-dione — the first naturally-occurring isoindole alkaloid — the peak potential was measured by DPP.

SYNTHESE UND POLAROGRAPHISCHES VERHALTEN VON 2H-ISOINDOL-4,7-DIONEN

Summary2-Phenylthio-1,4-benzoquinone (1 a) reacts with azomethine ylide AY-A to give 2-methyl-5-phenylthio-2H-isoindole-4,7-dione (4 f). With 2-(N-methylanilino)-5-methyl-1,4-benzoquinone (1 b), the azomethine ylide AY-B undergoes cycloaddition to yield an inseparable mixture of 5a-methyl-8-(N-methylanilino)-2,3,5,5a,9a,9b-hexahydro-pyrrolo[2,1-a]1H-isoindole-6,9-dione (5 bI) and 9a-methyl-7-(N-methylanilino)-2,3,5,5a,9a,9b-hexahydropyrrolo[2,1-a]1H-isoindole-6,9-dione (5 bII). The structures of5 bI and5 bII were established on basis of two-dimensional-NMR-techniques. The mechanism of the cycloaddition of azomethine ylides to 1,4-quinones was studied on basis of cyclovoltammetric investigations. To determine the electron affinity of the isoindoledione derivatives4 a–f and5 a–b the peak potentials were measured by differential pulse polarography (DPP).

Determination of 5-hydroxynaphthoquinones in phytotherapeutic Drosera preparations by differential pulse polarography

A differential pulse polarographic method is described for the determination of three pharmacologically active 5-hydroxynaphthoquinones in Drosera-containing phytomedicines available on the Austrian market. The polarographic behaviours of plumbagin, 7-methyljuglone and droserone were examined in various buffer systems in the pH-range from 3.5 to 10.0. The compounds were reduced in a single reversible peak at the dropping mercury electrode. The differential pulse polarograms of the naphthoquinones showed distinct peaks in sodium acetate/acetic acid buffer:methanol solution, and a plot of peak height against concentration was found to be linear over the range 0.16–30.0 µg/ml for droserone, 0.06–8.0 µg/ml for plumbagin and 0.16–25.0 µg/ml for 7-methyljuglone. The polarographic method was applied to determine the amounts of these naphthoquinones in three Drosera-containing phytomedicines. In one preparation the droserone concentrations, depending on the sample taken, were found to be 6.81 and 5.78 µg/ml, whilst in a second preparation the droserone concentrations were 1.87, 3.67 and 0.51 µg/ml. The content of plumbagin and 7-methyljuglone was lower than the polarographic detection limit (0.4 µg/ml of each). In a third preparation neither droserone, plumbagin, nor 7-methyljuglone were polarographically detectable (<0.2 µg/ml). Copyright

DETERMINATION OF NISOLDIPINE IN FILM TABLETS BY DIFFERENTIAL PULSE POLAROGRAPHY

SummaryA differential pulse polarographic (DPP) method was developed for the determination of nisoldipine in Baymycard® film tablets without interference from excipients. Nisoldipine is reduced at the dropping mercury electrode in a single, irreversible peak. Linearity between the nisoldipine concentration and the peak height was observed in the 5·10−4–10−7M concentration range. The detection limit is 22 ng/ml. The analysis of a series of 10 Baymycard® 5 mg film tablets showed a standard deviation of ±0.115 mg and aSrel of ±2.30%, respectively.ZusammenfassungEine Bestimmung von Nisoldipin in Baymycard® Filmtabletten mittels differentieller Pulspolarographie (DPP) wurde entwickelt, die keine Störungen durch Tablettenhilfsstoffe aufweist. Nisoldipin wird an der tropfenden Quecksilberelektrode in einem einzigen, irreversiblen Peak reduziert. Linearität zwischen Nisoldipinkonzentration und Peakhöhe wurde im Konzentrationsbereich von 5·10−4–10−7M festgestellt. Die Bestimmungsgrenze beträgt 22 ng/ml. Die Analyse einer Serie von 10 Baymycard® 5 mg Filmtabletten ergab eine Standardabweichung von ±0.115 mg, dies entspricht einerSrel von ±2.30%.

Gehaltsbestimmung von Oxybutyninhydrochlorid mittels differentieller Pulspolarographie

SummaryA differential pulse polarographic (DPP) method was developed for the determination of oxybutynine hydrochloride in Ditropan® tablets without interference from excipients. Oxybutynine reacts at the dropping mercury electrode resulting in two irreversible peaks. Linearity between the oxybutynine concentration and the peak height was observed in the 2×10−4−2.5×10−6M concentration range. The detection limit is 0.6 µg/ml. The analysis of a series of 10 Ditropan® 5 mg tablets showed a standard deviation of ±0.076 mg and aSrel of ±1.53%, respectively.

Determination of acipimox in capsules by differential pulse polarography

A differential pulse polarographic (DPP) method has been developed for the determination of acipimox in its pharmaceutical formulations. Using Sörensen buffer pH 6.0 as supporting electrolyte a single, irreversible peak occurred at −0.79 V vs an Ag/AgCl reference electrode. The peak height vs concentration plot was found to be linear over the range of 10−6 to 6 × 10−4 mol/l. The detection limit is 60ng/ml. The analysis of a series of 10 Olbetam® 250 mg capsules showed an overall standard deviation of ± 4.18 mg and a Srel of ± 1.66%, respectively.