A DPP study of ranitidine permeability

The apparent permeation rate constants and amount of ranitidine transferred in 1 h were measured through everted rat intestine using a perfusion apparatus. The effects of pH and 5% or 10% ethanol on the apparent permeation parameters were evaluated. A selective permeation at pH 7.4 in the jejunum was found for ranitidine. Both ethanol concentrations diminished the apparent permeability in this segment significantly. A good correlation was established between the apparent first-order permeation rate constants and the lipophilicity of the drugs as measured by their apparent partition coefficients. However, a significant contribution of the ionized species to the overall permeation process was determined. Under the experimental conditions employed here, a passive diffusion transport mechanism through the small intestine (jejunum) is followed for ranitidine. © 1988

A polarographic study of the photodegradation of nitrendipine

Nitrendipine produces a well-defined polarographic peak due to the four-electron reduction of the nitro group. This peak is used for tracking the photodecomposition of nitrendipine in both UV light and daylight conditions. The results show that nitrendipine remains unaltered in the short time scale of a normal analytical procedure and no special care with visible light exposure is necessary. However nitrendipine is strongly altered with UV irradiation showing a first-order degradation kinetics. A degradation rate constant of 0.0665 min-1 with a t 1 2, of 10.423 min has been obtained. The UV degradation product was isolated and identified as the nitro pyridine analogue of nitrendipine. © 1990

A DPP study of ranitidine permeability

The apparent permeation rate constants and amount of ranitidine transferred in 1 h were measured through everted rat intestine using a perfusion apparatus. The effects of pH and 5% or 10% ethanol on the apparent permeation parameters were evaluated. A selective permeation at pH 7.4 in the jejunum was found for ranitidine. Both ethanol concentrations diminished the apparent permeability in this segment significantly. A good correlation was established between the apparent first-order permeation rate constants and the lipophilicity of the drugs as measured by their apparent partition coefficients. However, a significant contribution of the ionized species to the overall permeation process was determined. Under the experimental conditions employed here, a passive diffusion transport mechanism through the small intestine (jejunum) is followed for ranitidine. © 1988

Nitro radical anion formation from nimodipine

Voltammetric studies of nimodipine using a mixed aqueous dimethylformamide (DMF) solvent have allowed us to generate the one-electron reduction product, the nitro radical anion RNO2 .. The cyclic voltammetry technique has been employed to study the tendency of RNO2 . to undergo further chemical reactions. This subsequent chemical reaction corresponds to a second-order process, a dismutation reaction which is initiated electrochemically. Data for rate constants and half-lives at pH 8.2 were determined in aqueous DMF media. A method which is able to generate selectively the RNO2 . species electrochemically and to study its in-situ reactions is proposed. © 1993

Unexpected diastereotopic behaviour in the ¹H NMR spectrum of 1,4-dihydropyridine derivatives triggered by chiral and prochiral centres

1,4-dihydropyridine derivatives constitute an important pharmacological group for the treatment of cardiovascular diseases. We have synthesised a series 4-(5'-nitro-2'-furyl)-1,4-dihydropyridine derivatives, which were characterised by ¹H-NMR. We have found that carboethoxy groups at the C-3 and C-5 on the 1,4-dihydropyridine ring show a much more complex signal in the ¹H NMR spectra, either when C-4 is a pseudo-prochiral or a chiral centre

Dihydropyridine-fused and pyridine-fused coumarins: Reduction on a glassy carbon electrode in dimethylformamide

In this study, two series of dihydropyridine-fused and pyridine-fused coumarins were synthesised and electrochemically characterised in aprotic medium. In both series, the most easily reducible groups were the endocyclic carbonyl groups. The electrochemical mechanism for both types of compounds is strongly dependent on the experimental time-scale. Cyclic voltammetric (CV) reduction on a glassy carbon electrode (GCE) of the endocyclic carbonyl group of dihydropyridine-fused coumarins involves an ECEC mechanism with two electron transfer steps that are coupled with chemical reactions to produce the corresponding hemiacetal derivative. In the case of pyridine-fused coumarins, CV reduction of the endocyclic carbonyl group involves an EEC mechanism. ESR studies revealed the presence of a stabilised intermediate only for the pyridine-fused derivatives. Our theoretical study showed a spin density map of radical species delocalised mainly within the coumarin ring, indicating the reduction of