Polycyclic Polyprenylated Xanthones from Symphonia globulifera: Isolation and Biomimetic Electrosynthesis.

Two regioisomeric polycyclic xanthones, 3,16-oxyguttiferone A (2) and 1,16-oxyguttiferone A (3), which are polyprenylated acylphloroglucinol-derived analogues, were isolated from the seeds of Symphonia globulifera, together with their presumed o-dihydroxybenzoyl precursor, guttiferone A (1). Anodic oxidation of 1 into the corresponding o-quinone species proved to be an efficient biomimetic method to generate xanthones 2 and 3 in high overall yield and to confirm their structures. Both compounds displayed cytotoxicity against the HCT 116 colon carcinoma cell line with IC50 values of 8 and 3 µM, respectively.

Synthesis and neurotoxicity profile of 2,4,5-trihydroxymethamphetamine and its 6-(N-acetylcystein-S-yl) conjugate.

The purpose of the present study was to determine if trihydroxymethamphetamine (THMA), a metabolite of methylenedioxymethamphetamine (MDMA, "ecstasy"), or its thioether conjugate, 6-(N-acetylcystein-S-yl)-2,4,5-trihydroxymethamphetamine (6-NAC-THMA), play a role in the lasting effects of MDMA on brain serotonin (5-HT) neurons. To this end, novel high-yield syntheses of THMA and 6-NAC-THMA were developed. Lasting effects of both compounds on brain serotonin (5-HT) neuronal markers were then examined. A single intraventricular injection of THMA produced a significant lasting depletion of regional rat brain 5-HT and 5-hydroxyindoleacetic acid (5-HIAA), consistent with previous reports that THMA harbors 5-HT neurotoxic potential. The lasting effect of THMA on brain 5-HT markers was blocked by the 5-HT uptake inhibitor fluoxetine, indicating that persistent effects of THMA on 5-HT markers, like those of MDMA, are dependent on intact 5-HT transporter function. Efforts to identify THMA in the brains of animals treated with a high, neurotoxic dose (80 mg/kg) of MDMA were unsuccessful. Inability to identify THMA in the brains of these animals was not related to the unstable nature of the THMA molecule because exogenous THMA administered intracerebroventricularly could be readily detected in the rat brain for several hours. The thioether conjugate of THMA, 6-NAC-THMA, led to no detectable lasting alterations of cortical 5-HT or 5-HIAA levels, indicating that it lacks significant 5-HT neurotoxic activity. The present results cast doubt on the role of either THMA or 6-NAC-THMA in the lasting serotonergic effects of MDMA. The possibility remains that different conjugated forms of THMA or oxidized cyclic forms (e.g., the indole of THMA) play a role in MDMA-induced 5-HT neurotoxicity in vivo.

A small molecule that mimics the metabolic activity of copper-containing amine oxidases (CuAOs) toward physiological mono- and polyamines.

Primary aliphatic biogenic amines have been successfully oxidized using a quinonoid species that mimics the metabolic activity of copper-containing amine oxidase (CuAO) enzymes. Especially, high catalytic performances were observed with aminoacetone, a threonine catabolite, and methylamine, a metabolite of adrenaline, and with the primary amino groups of putrescine and spermidine which are both decarboxylation products of ornithine and S-adenosyl-methionine. Furthermore, contrary to flavine adenine dinucleotide (FAD)-dependent amine oxidase enzymes, no activity was found toward secondary and tertiary amines.

Synthesis and in vitro cytotoxicity profile of the R-enantiomer of 3,4-dihydroxymethamphetamine (R-(-)-HHMA): comparison with related catecholamines.

(+/-)-3,4-Methylenedioxymethamphetamine (MDMA, also known as "ecstasy") is a chiral drug that is essentially metabolized in humans through O-demethylenation into 3,4-dihydroxymethamphetamine (HHMA). There has recently been a resurgence of interest in the possibility that MDMA metabolites, especially 5-(N-acetylcystein-S-yl)-N-methyl-alpha-methyldopamine (designated as 5-NAC-HHMA), might play a role in MDMA neurotoxicity. However, the chirality of MDMA was not considered in previously reported in vivo studies because HHMA, the precursor of the 5-NAC-HHMA metabolite, was used as the racemate. Since the stereochemistry of this chiral drug needs to be considered, the first total synthesis of R-(-)-HHMA is reported. Using L-DOPA as the chiral source, the preparation of R-(-)-HHMA is achieved through seven steps, in 30% overall yield and 99.5% enantiomeric excess. The cytotoxicity of R-(-)-HHMA and related catecholamines has been further determined by flow cytometric analysis of propidium iodide uptake in human dopaminergic neuroblastoma SH-SY5Y cells and by an Escherichia coli plate assay, specific for the detection of oxidative toxicity. The good correlation between the toxicities observed in both systems suggests that SH-SY5Y cells are sensitive to oxidative toxicity and that cell death (necrosis) would be mediated by reactive oxygen species mainly generated from redox active quinonoid centers. In contrast, apoptosis was detected for 3,4-dimethoxymethamphetamine (MMMA), the synthetic precursor of HHMA possessing a protected catechol group. MMMA was not toxic in the bacterial assay, indicating that its toxicity is not related to increased oxidative stress. Finally, we can conclude that there is a need to distinguish the toxicity ascribed to MDMA itself, also bearing a protected catechol moiety, from that depending on MDMA biotransformation leading to catechol metabolites such as HHMA and the thioether conjugates.

Bacterial plate assays and electrochemical methods: an efficient tandem for evaluating the ability of catechol-thioether metabolites of MDMA ("ecstasy") to induce toxic effects through redox-cycling.

Several catechol-thioether metabolites of MDMA (ecstasy), three monoadducts, 5-(glutathion-S-yl)-N-methyl-alpha-methyldopamine (1), 5-(N-acetylcystein-S-yl)-N-methyl-alpha-methyldopamine (2), and 5-(cystein-S-yl)-N-methyl-alpha-methyldopamine (3), and two bi-adducts, 2,5-bis(glutathion-S-yl)-N-methyl-alpha-methyldopamine (4) and 2,5-bis(N-acetylcystein-S-yl)-N-methyl-alpha-methyldopamine (5), have been synthesized through an environmentally friendly one-pot electrochemical procedure. Their cytotoxicity profiles were further characterized using simple Escherichia coli plate assays and compared with those of N-methyl-alpha-methyldopamine (HHMA), dopamine (DA), and its corresponding catechol-thioether conjugates (monoadducts 6-8 and bi-adducts 9 and 10). Toxicity mediated by reactive oxygen species (ROS-TOX) was detected in the OxyR- assay, using cells sensitive to oxidative stress due to a deficiency in the OxyR protein. Toxicity arising from the high susceptibility of quinone toward endogenous nucleophiles (Q-TOX) was detected using OxyR+ cells, in the presence of tyrosinase, to promote catechol oxidation to the corresponding o-quinone. At the exclusion of 5-(cystein-S-yl) mono-conjugate 3, which was devoid of any toxicity, all compounds produced ROS-TOX, which was enhanced in the presence of tyrosinase, suggesting that the generated o-quinone (or o-quinone-thioether) species can enter redox cycles through its semiquinone radical, leading to the formation of ROS. The sequence order of toxicity was HHMA approximately = 1 approximately = 2 approximately =5 >> 7 > DA approximately = 4 > 10 > 6 > 8. In contrast, no Q-TOX arising from the binding of quinones with cellular nucleophiles was evidenced, even in the presence of tyrosinase. Finally, taking into account that several different pathways could contribute to the overall MDMA toxicity and that HHMA and catechol-thioether conjugates 1-5 have not been undoubtedly established as in vivo toxic metabolites of MDMA, it can be suggested that these compounds could participate in the toxic effects of this drug through the efficiency of redox active quinonoid centers generating ROS.

A convenient approach for evaluating the toxicity profiles of in vitro neuroprotective alkylaminophenol derivatives.

The cytotoxicity profiles of a series of quinol-type derivatives were examined through simple Escherichia coli plate assays discriminating the two main cytotoxicity mechanisms associated with polyphenol oxidation to quinone. Toxicity mediated by reactive oxygen species (ROS-TOX) was detected in the OxyR(-) assay using cells sensitive to oxidative stress due to a deficiency in the OxyR function. Toxicity arising from the high susceptibility of quinone toward endogenous nucleophiles (Q-TOX) was detected using OxyR(+) cells, in the presence of a nitric oxide donor to promote the quinol oxidation to the corresponding quinone. The toxicity profile markedly depended on structural features. Strong ROS-TOX required a pyrogallol arrangement (exifone; 2,3,4-trihydroxybenzophenone, 1; baicalein) or a 2-aminoresorcinol sequence (3-amino-2,4-dihydroxybenzophenone, 4). The pyrogallol moiety determined a low Q-TOX, suggesting the conversion of quinones into oxidation products of low toxicity. Compounds lacking a 2-hydroxyl substituent (derivatives 2 and 5, related to 1 and 4, respectively) induced a weak ROS-TOX, but a significant Q-TOX. The electrochemical oxidation of the studied compounds corroborated the crucial role of the 2-hydroxyl group, which had two effects: to protect the quinonoid species from Michael addition, the reaction at the origin of Q-TOX, and, due to the contraction of hydrogen bonding, to stabilize every intermediary oxidation product, very likely involved in ROS-TOX.