In order to explain the potent antihypertensive activity of the modestly active (IC50 = 3.2 microM) dihydropyrimidine calcium channel blocker 5, we carried out drug metabolism studies in the rat and found 5 is metabolized to compounds 6-10. Two of the metabolites, 6 (IC50 = 16 nM) and 7 (IC50 = 12 nM), were found to be responsible for the antihypertensive activity of compound 5. Potential metabolism of 6 into 7 in vivo precluded our interest in pursuing compounds related to 6. Structure-activity studies aimed at identifying additional aryl-substituted analogues of 7 led to 17g,j,p with comparable potential in vivo, though these compounds were less potent than 7 in vitro. To investigate the effects of absolute stereochemistry on potency, we resolved 7 via diastereomeric ureas 19a,b, prepared from 18 by treatment with (R)-alpha-methylbenzylamine. Our results demonstrate that the active R-(-)-enantiomer 20a of 7 is both more potent and longer acting than nifedipine (1) as an antihypertensive agent in the SHR. The in vivo potency and duration of 20a is comparable to the long-acting dihydropyridine amlodipine. The superior oral antihypertensive activity of 20a compared to that of previously described carbamates 2 (R2 = COOEt) could be explained by its improved oral bioavailability, possibly resulting from increased stability of the urea functionality.

The catecholamines, alpha-methyldopamine (alpha-MeDA) and dopamine (DA), have been implicated in 3,4-(methylenedioxy)amphetamine (MDA) toxicity. The toxicity and metabolic fate of alpha-MeDA, a metabolite of MDA, and DA, a neurotransmitter released by MDA administration, were examined in NG108-15 cells. Both catechols were found to accumulate intracellularly into NG108-15 cells. alpha-MeDA was about 4 times more toxic than DA in the cells. The depletion of glutathione (GSH) by buthionine sulfoximine (BSO) resulted in a drastic increase (10 times) in the alpha-MeDA mediated toxicity while the toxicity of DA was enhanced by 2 times. DA was largely metabolized to dihydroxyphenylacetic acid (DOPAC) and, to a smaller extent, formed an adduct with GSH. alpha-MeDA was primarily metabolized to a GSH adduct. alpha-MeDA was also metabolized to a product which was identified as the cysteinyl adduct. These adducts were identified by HPLC coelution with authentic standards. The GSH and cysteinyl adducts are presumably formed through conjugation of the thiols with intermediary quinone oxidation products of DA and alpha-MeDA. Previous studies indicate that alpha-MeDA is significantly more toxic than DA, especially under conditions of GSH depletion. The results of this study suggest that alpha-MeDA toxicity may occur through cytoplasmic accumulation and oxidation to a reactive quinone species followed by reaction with vital thiol functions or generation of reactive oxygen species. Cytoplasmic DA levels, on the other hand, appear to be significantly lower due to MAO metabolism and vesicular storage, and therefore, DA appears less likely to form conjugates with thiol groups or participate in possible redox cycling.

No abstract

The backbone of effective highly active antiretroviral therapy regimens for the treatment of HIV infections currently contains at least two nucleosides. Among the features that influence the potency of each component of a regimen and the overall efficacy of the combination are the cellular uptake and bioconversion of nucleoside analogues to their active triphosphate form, and the extent of possible interactions in these steps that might occur when more than one nucleoside is used in a regimen. D-d4FC (Reverset), a new cytidine analogue with the ability to inhibit many nucleoside-resistant viral variants, was examined for these parameters. In phytohemaglutinin-stimulated human peripheral blood mononuclear cells, D-d4FC was taken up in a rapid (8 h to 50% maximal value), saturable (plateau above 10 microM parent nucleoside concentration) process, resulting in levels of D-d4FC triphosphate that should provide potent antiviral activity against a variety of virus genotypes. Based on measurement of antiviral effects in cell culture, additive and in some cases, synergistic interactions were observed with protease inhibitors, non-nucleoside reverse transcriptase inhibitors or other nucleosides, including cytidine analogues.