Caffeic acid, tyrosol and p-coumaric acid are potent inhibitors of 5-S-cysteinyl-dopamine induced neurotoxicity

Parkinson’s disease is characterized by a progressive and selective loss of dopaminergic neurons in the substantia nigra. Recent investigations have shown that conjugates such as the 5-S-cysteinyl-dopamine, possess strong neurotoxicity and may contribute to the underlying progression of the disease pathology. Although the neuroprotective actions of flavonoids are well reported, that of hydroxycinnamates and other phenolic acids is less established. We show that the hydroxycinnamates caffeic acid and p-coumaric acid, the hydroxyphenethyl alcohol, tyrosol, and a Champagne wine extract rich in these components protect neurons against injury induced by 5-S-cysteinyl-dopamine in vitro. The protection induced by these polyphenols was equal to or greater than that observed for the flavonoids, (+)-catechin, (−)-epicatechin and quercetin. For example, p-coumaric acid evoked significantly more protection at 1 μM (64.0 ± 3.1%) than both (−)-epicatechin (46.0 ± 4.1%, p < 0.05) and (+)-catechin (13.1 ± 3.0%, p < 0.001) at the same concentration. These data indicate that hydroxycinnamates, phenolic acids and phenolic alcohol are also capable of inducing neuroprotective effects to a similar extent to that seen with flavonoids.     

Irreversible Inhibition of Mitochondrial Complex I by 7-(2-Aminoethyl)-3,4-Dihydro-5-Hydroxy-2H-1,4-Benzothiazine-3-Carboxylic Acid (DHBT-1): A Putative Nigral Endotoxin of Relevance to Parkinson's Disease

Abstract: Based on a number of lines of evidence, we have proposed recently that a very early step in the pathogenesis of idiopathic Parkinson's disease might be elevated translocation of l -cysteine into neuromelanin-pigmented dopaminergic cell bodies in the substantia nigra. In vitro studies suggest that such an influx of l -cysteine would divert the neuromelanin pathway by scavenging dopamine-o-quinone, the proximate autoxidation product of dopamine, to give 5-S-cysteinyldopamine, which is oxidized further to 7-(2-aminoethyl)-3,4-dihydro-5-hydroxy-2H-1,4-benzothiazine-3-carboxylic acid (DHBT-1) and other cysteinyldopamines and dihydrobenzothiazines. In this study, it is demonstrated that DHBT-1 inhibits ADP-stimulated oxidation of malate and pyruvate (state 3 or complex I respiration) when incubated with intact rat brain mitochondria with an IC₅₀ of ～0.80 mM. Incubation of DHBT-1 with freeze-thawed rat brain mitochondria in both the presence and absence of KCN and/or NADH causes an irreversible, time-dependent decrease of NADH-coenzyme Q₁ reductase activity. Significantly lower concentrations of DHBT-1 are necessary to cause this effect when mitochondrial membranes are incubated in the absence of KCN and NADH. The irreversible inhibition of mitochondrial complex I caused by DHBT-1 under the latter conditions could be blocked only partially by glutathione, ascorbic acid, superoxide dismutase, or catalase. Together, these results suggest that DHBT-1 can cross the outer mitochondrial membrane and irreversibly inhibit complex I by a mechanism that is not primarily related to oxygen radical-mediated damage. Formation of DHBT-1 requires only dopamine, l -cysteine, and an oxidizing environment, conditions that may well exist in the cytoplasm of neuromelanin-pigmented dopaminergic neurons in the parkinsonian substantia nigra. The results of this study raise the possibility that DHBT-1 might be an endotoxin formed specifically in pigmented dopaminergic neurons that can contribute to irreversible damage to mitochondrial complex I and substantia nigra cell death in Parkinson's disease.     

Substrate specificity of human glutamine transaminase K as an aminotransferase and as a cysteine S-conjugate beta-lyase

Rat kidney glutamine transaminase K (GTK) exhibits broad specificity both as an aminotransferase and as a cysteine S-conjugate β-lyase. The β-lyase reaction products are pyruvate, ammonium and a sulfhydryl-containing fragment. We show here that recombinant human GTK (rhGTK) also exhibits broad specificity both as an aminotransferase and as a cysteine S-conjugate β-lyase. S-(1,1,2,2-Tetrafluoroethyl)-l-cysteine is an excellent aminotransferase and β-lyase substrate of rhGTK. Moderate aminotransferase and β-lyase activities occur with the chemopreventive agent Se-methyl-l-selenocysteine. l-3-(2-Naphthyl)alanine, l-3-(1-naphthyl)alanine, 5-S-l-cysteinyldopamine and 5-S-l-cysteinyl-l-DOPA are measurable aminotransferase substrates, indicating that the active site can accommodate large aromatic amino acids. The α-keto acids generated by transamination/l-amino acid oxidase activity of the two catechol cysteine S-conjugates are unstable. A slow rhGTK-catalyzed β-elimination reaction, as measured by pyruvate formation, was demonstrated with 5-S-l-cysteinyldopamine, but not with 5-S-l-cysteinyl-l-DOPA. The importance of transamination, oxidation and β-elimination reactions involving 5-S-l-cysteinyldopamine, 5-S-l-cysteinyl-l-DOPA and Se-methyl-l-selenocysteine in human tissues and their biological relevance are discussed.     

Steroidal saponins from the leaves of Beaucarnea recurvata

Thirteen steroidal saponins were isolated from the leaves of Beaucarnea recurvata Lem. Their structures were established using one- and two-dimensional NMR spectroscopy and mass spectrometry. Six of them were identified as: 26-O-β-d-glucopyranosyl (25S)-furosta-5,20(22)-diene 1β,3β,26-triol 1-O-α-l-rhamnopyranosyl-(1 → 2) β-d-fucopyranoside, 26-O-β-d-glucopyranosyl (25S)-furosta-5,20(22)-diene 1β,3β,26-triol 1-O-α-l-rhamnopyranosyl-(1 → 2)-4-O-acetyl-β-d-fucopyranoside, 26-O-β-d-glucopyranosyl (25R)-furosta-5,20(22)-diene-23-one-1β,3β,26-triol 1-O-α-l-rhamnopyranosyl-(1 → 2) β-d-fucopyranoside, 26-O-β-d-glucopyranosyl (25S)-furosta-5-ene-1β,3β,22α,26-tetrol 1-O-α-l-rhamnopyranosyl-(1 → 4)-6-O-acetyl-β-d-glucopyranoside, 26-O-β-d-glucopyranosyl (25S)-furosta-5-ene-1β,3β,22α,26-tetrol 1-O-α-l-rhamnopyranosyl-(1 → 2) β-d-fucopyranoside, and 24-O-β-d-glucopyranosyl (25R)-spirost-5-ene-1β,3β,24-triol 1-O-α-l-rhamnopyranosyl-(1 → 2)-4-O-acetyl-β-d-fucopyranoside. The chemotaxonomic classification of B. recurvata in the family Ruscaceae was discussed.     

Brain Mitochondria Catalyze the Oxidation of 7-(2-Aminoethyl)-3,4-Dihydro-5-Hydroxy-2H-1,4-Benzothiazine-3-Carboxylic Acid (DHBT-1) to Intermediates that Irreversibly Inhibit Complex I and Scavenge Glutathione: Potential Relevance to the Pathogenesis of Parkinson's Disease

Abstract: We have proposed that a very early step in the pathogenesis of idiopathic Parkinson's disease is the elevated translocation of l -cysteine into neuromelanin-pigmented dopaminergic neurons in the substantia nigra. This influx of l -cysteine was proposed to divert the normal neuromelanin pathway by scavenging dopamine-o-quinone, formed by autoxidation of cytoplasmic dopamine, to give initially 5-S-cysteinyldopamine, which is further oxidized to 7 - (2 - aminoethyl) - 3,4 - dihydro - 5 - hydroxy - 2H - 1,4 - benzothiazine-3-carboxylic acid (DHBT-1). In a recent report, it was demonstrated that DHBT-1 evokes inhibition of complex I respiration when incubated with intact rat brain mitochondria and a time-dependent irreversible inhibition of NADH-coenzyme Q₁ (CoQ₁) reductase when incubated with mitochondrial membranes. In this study, it is established that the time dependence of NADH-CoQ₁ reductase inhibition reflects the oxidation of DHBT-1, catalyzed by an unknown constituent of the inner mitochondrial membrane, to an o-quinone imine intermediate that rearranges to 7-(2-aminoethyl) - 5 - hydroxy - 1,4 - benzothiazine - 3 - carboxylic acid (BT-1) and decarboxylates to 7-(2-aminoethyl)-5-hydroxy-1,4-benzothiazine (BT-2), which are further catalytically oxidized to o-quinone imine intermediates. The electrophilic o-quinone imine intermediates formed in these mitochondria-catalyzed oxidations of DHBT-1, BT-1, and BT-2 are proposed to bind covalently to key sulfhydryl residues at the complex I site, thus evoking irreversible inhibition of NADH-CoQ₁ reductase. Evidence for this mechanism derives from the fact that greater than equimolar concentrations of glutathione completely block inhibition of NADH-CoQ₁ reductase by DHBT-1, BT-1, and BT-2 by scavenging their electrophilic o-quinone imine metabolites to form glutathionyl conjugates. The results of this investigation may provide insights into the irreversible loss of glutathione and decreased mitochondrial complex I activity, which are both anatomically specific to the substantia nigra and exclusive to Parkinson's disease.     

4-O-methylhonokiol attenuated β-amyloid-induced memory impairment through reduction of oxidative damages via inactivation of p38 MAP kinase

Oxidative stress induced neuronal cell death by accumulation of β-amyloid (Aβ) is a critical pathological mechanism of Alzheimer's disease (AD). Intracerebroventrical infusion of Aβ_1-42 (300 pmol/day per mouse) for 14 days induced neuronal cell death and memory impairment, but pre-treatment of 4-O-methylhonokiol (4-O-MH), a novel compound extracted from Magnolia officinalis for 3 weeks (0.2, 0.5 and 1.0 mg/kg) prior to the infusion of Aβ_1-42 and during the infusion dose dependently improved Aβ_1-42-induced memory impairment and prevented neuronal cell death. Additionally, 4-O-MH reduced Aβ_1-42 infusion-induced oxidative damages of protein and lipid but reduced glutathione levels in the cortex and hippocampus. Aβ_1-42 infusion-induced activation of astrocytes and p38 mitogenic activated protein (MAP) kinase was also prevented by 4-O-MH in mice brains. In further study using culture cortical neurons, p38 MAP kinase inhibitor abolished the inhibitory effect of 4-O-MH (10 μM) on the Aβ_1-42 (5 μM)-induced reactive oxidative species generation and neuronal cell death. These results suggest that 4-O-MH might prevent the development and progression of AD through the reduction of oxidative stress and neuronal cell death via inactivation of p38 MAP kinase pathway.     

Aporphine alkaloids and cytotoxic lignans from the roots of Illigera luzonensis

Six aporphine alkaloids, (+)-(S)-N-butyrylcaaverine (1), (+)-(S)-N-propionylcaaverine (2), (+)-(S)-N-acetylcaaverine (3), (+)-(6aR,7R)-N-butyrylnorushinsunine (4), (+)-(6aR,7R,E)-N-(but-2-enoyl)norushinsunine (5), and N-formyldehydrocaaverine (6) were isolated from the roots of Illigera luzonensis, together with 16 known compounds. Their structures were determined through spectroscopic and MS analyses. Among the isolates, (−)-deoxypodophyllotoxin (13) was the most cytotoxic, with IC₅₀ values of 0.0057, 0.0067, 0.00004, and 0.0035 μg/mL, respectively, against DLD-1, CCRF-CEM, HL-60, and IMR-32 cell lines. In addition, (−)-yatein (12) exhibited cytotoxic effects, with IC₅₀ values of 0.81, 0.20, and 0.59 μg/mL, respectively, against DLD-1, CCRF-CEM, and HL-60 cell lines.     

Monoterpenoids from the aerial parts of Aruncus dioicus var. kamtschaticus and their antioxidant and cytotoxic activities

The aerial parts of Aruncus dioicus var. kamtschaticus afforded five new monoterpenoids (1-5): 4-(erythro-6,7-dihydroxy-9-methylpent-8-enyl)furan-2(5H)-one (1, aruncin A), 2-(8-ethoxy-8-methylpropylidene)-5-hydroxy-3,6-dihydro-2H-pyran-4-carboxylic acid (2, aruncin B), 4-(hydroxymethyl)-6-(8-methylprop-7-enyl)-5,6-dihydro-2H-pyran-2-one-11-O-β-d-glucopyranoside (3, aruncide A), (3S,4S,5R,10R)-3-(10-ethoxy-11-hydroxyethyl)-4-(5-hydroxy-7-methylbut-6-enyl)oxetan-2-one-11-O-β-d-glucopyranoside (4, aruncide B), and (3S,4S,5R,7R)-5-(9-methylprop-8-enyl)-1,6-dioxabicyclo[3,2,0]heptan-2-one-7-(hydroxymethyl)-12-O-β-d-glucopyranoside (5, aruncide C). Compound 2 showed potent cytotoxicity against Jurkat T cells with an IC₅₀ value of 17.15 μg/mL. In addition, compounds 7 and 10 exhibited moderate antioxidant activity with IC₅₀ values of 46.3 and 11.7 μM, respectively.     

Neuroprotection of the leaf and stem of Vitis amurensis and their active compounds against ischemic brain damage in rats and excitotoxicity in cultured neurons

Vitis amurensis (Vitaceae) has been reported to have anti-oxidant and anti-inflammatory activities. The present study investigated a methanol extract from the leaf and stem of V. amurensis for neuroprotective effects on cerebral ischemic damage in rats and on excitotoxicity induced by glutamate in cultured rat cortical neurons. Transient focal cerebral ischemia was induced by 2 h middle cerebral artery occlusion followed by 24 h reperfusion (MCAO/reperfusion) in rats. Orally administered V. amurensis (25-100 mg/kg) reduced MCAO/reperfusion-induced infarct and edema formation, neurological deficits, and neuronal death. Depletion of glutathione (GSH) level and lipid peroxidation induced by MCAO/reperfusion was inhibited by administration of V. amurensis. The increase of phosphorylated mitogen-activated protein kinases (MAPKs), cyclooxygenase-2 (COX-2), and pro-apoptotic proteins and the decrease of anti-apoptotic protein in MCAO/reperfusion rats were significantly inhibited by treatment with V. amurensis. Exposure of cultured cortical neurons to 500 μM glutamate for 12 h induced neuronal cell death. V. amurensis (1-50 μg/ml) and (+)-ampelopsin A, γ-2-viniferin, and trans-?-viniferin isolated from the leaf and stem of V. amurensis inhibited glutamate-induced neuronal death, the elevation of intracellular calcium ([Ca²⁺]_i), the generation of reactive oxygen species (ROS), and changes of apoptosis-related proteins in cultured cortical neurons, suggesting that the neuroprotective effect of V. amurensis may be partially attributed to these compounds. These results suggest that the neuroprotective effect of V. amurensis against focal cerebral ischemic injury might be due to its anti-apoptotic effect, resulting from anti-excitotoxic, anti-oxidative, and anti-inflammatory effects and that the leaf and stem of V. amurensis have possible therapeutic roles for preventing neurodegeneration in stroke.     

Cycloartane-type glycosides from Astragalus amblolepis

Five cycloartane-type triterpene glycosides were isolated from the methanol extract of the roots of Astragalus amblolepis Fischer along with one known saponin, 3-O-β-D-xylopyranosyl-16-O-β-D-glucopyranosyl-3β,6α,16β,24(S),25-pentahydroxy-cycloartane. Structures of the compounds were established as 3-O-β-D-xylopyranosyl-25-O-β-D-glucopyranosyl-3β,6α,16β,24(S),25-pentahydroxy-cycloartane, 3-O-[β-D-glucuronopyranosyl-(1 → 2)-β-D-xylopyranosyl]-25-O-β-D-glucopyranosyl-3β,6α,16β,24(S),25-pentahydroxy-cycloartane, 3-O-β-D-xylopyranosyl-24,25-di-O-β-D-glucopyranosyl-3β,6α,16β,24(S),25-pentahydroxy-cycloartane, 6-O-α-L-rhamnopyranosyl-16,24-di-O-β-D-glucopyranosyl-3β,6α,16β,24(S),25-pentahydroxy-cycloartane, 6-O-α-L-rhamnopyranosyl-16,25-di-O-β-D-glucopyranosyl-3β,6α,16β,24(S),25-pentahydroxy-cycloartane by using 1D and 2D-NMR techniques and mass spectrometry. To the best of our knowledge, the glucuronic acid moiety in cycloartanes is reported for the first time.     

Steroids from the leaves of Chinese Melia azedarach and their cytotoxic effects on human cancer cell lines

Three new (1-3) and several known (4-6) steroids were isolated from the leaves of Chinese Melia azedarach. The structures of the new compounds were elucidated by means of spectroscopic methods including 2D NMR techniques and mass spectrometry to be (20S)-5,24(28)-ergostadiene-3β,7α,16β,20-tetrol (1), (20S)-5-ergostene-3β,7α,16β,20-tetrol (2), and 2α,3β-dihydro-5-pregnen-16-one (3). The cytotoxicities of the isolated compounds against three human cancer cell lines (A549, H460, U251) were evaluated; only compounds 1, 2, and (20S)-5-stigmastene-3β,7α,20-triol (4) were found to show significant cyctotoxic effects with IC₅₀s from 12.0 to 30.1 μg/mL.     

Stereochemical Features of Glutathione-dependent Enzymes in the Sphingobium sp. Strain SYK-6 β-Aryl Etherase Pathway

Glutathione-dependent enzymes play important protective, repair, or metabolic roles in cells. In particular, enzymes in the glutathione S-transferase (GST) superfamily function in stress responses, defense systems, or xenobiotic detoxification. Here, we identify novel features of bacterial GSTs that cleave β-aryl ether bonds typically found in plant lignin. Our data reveal several original features of the reaction cycle of these GSTs, including stereospecific substrate recognition and stereoselective formation of β-S-thioether linkages. Products of recombinant GSTs (LigE, LigP, and LigF) are β-S-glutathionyl-α-keto-thioethers that are degraded by a β-S-thioetherase (LigG). All three Lig GSTs produced the ketone product (β-S-glutathionyl-α-veratrylethanone) from an achiral side chain-truncated model substrate (β-guaiacyl-α-veratrylethanone). However, when β-etherase assays were conducted with a racemic model substrate, β-guaiacyl-α-veratrylglycerone, LigE- or LigP-catalyzed reactions yielded only one of two potential product (β-S-glutathionyl-α-veratrylglycerone) epimers, whereas the other diastereomer (differing in configuration at the β-position (i.e. its β-epimer)) was produced only in the LigF-catalyzed reaction. Thus, β-etherase catalysis causes stereochemical inversion of the chiral center, converting a β(R)-substrate to a β(S)-product (LigE and LigP), and a β(S)-substrate to a β(R)-product (LigF). Further, LigG catalyzed glutathione-dependent β-S-thioether cleavage with β-S-glutathionyl-α-veratrylethanone and with β(R)-configured β-S-glutathionyl-α-veratrylglycerone but exhibited no or significantly reduced β-S-thioether-cleaving activity with the β(S)-epimer, demonstrating that LigG is a stereospecific β-thioetherase. We therefore propose that multiple Lig enzymes are needed in this β-aryl etherase pathway in order to cleave the racemic β-ether linkages that are present in the backbone of the lignin polymer.     

Cycloartane glycosides from Astragalus campylosema Boiss. ssp. campylosema

Four cycloartane glycosides, 3-O-[α-l-arabinopyranosyl-(1 → 2)-β-d-xylopyranosyl]-3β,6α,16β,23α,25-pentahydroxy-20(R),24(S)-epoxycycloartane (1), 3-O-[α-l-arabinopyranosyl-(1 → 2)-β-d-xylopyranosyl]-16-O-hydroxyacetoxy-23-O-acetoxy-3β,6α,25-trihydroxy-20(R),24(S)-epoxycycloartane (2), 3-O-[α-l-arabinopyranosyl-(1 → 2)-β-d-xylopyranosyl]-3β,6α,23α,25-tetrahydroxy-20(R),24(R)-16β,24;20,24-diepoxycycloartane (3), 3-O-[α-l-arabinopyranosyl-(1 → 2)-β-d-xylopyranosyl]-25-O-β-d-glucopyranosyl-3β,6α,16β,25-tetrahydroxy-20(R),24(S)-epoxycycloartane (4), along with three known cycloartane glycosides were isolated from the MeOH extract of the roots of Astragalus campylosema ssp. campylosema. Their structures were established by the extensive use of 1D- and 2D-NMR experiments along with ESIMS and HRMS analysis. The occurrence of the hydroxyl function at position 23 (1-2) and of the ketalic function at C-24 (3) are very unusual findings in the cycloartane class.     

New cytotoxic dihydrochalcone and steroidal saponins from the aerial parts of Sansevieria cylindrica Bojer ex Hook

A new dihydrochalcone, 2‘,4‘-dihydroxy-3‘-methoxy-3,4-methylenedioxy-8-hydroxymethylene dihydrochalcone 1 and two new steroidal saponins, (25S)-ruscogenin-1-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranoside 2, (25S)-ruscogenin-3-O-α-l-rhamnopyranosyl-(1 → 4)-β-d-glucopyranoside 3, together with three known steroidal saponins (25S)-ruscogenin-3-O-β-d-glucopyranoside 4, (25S)-ruscogenin-1-O-α-l-rhamnopyranosyl-(1 → 2)-[β-d-xylopyranosyl-(1 → 3)]-α-l-arabinopyranoside 5 and (25R)-26-O-β-d-glucopyranosyl-furost-5-ene-1β,3β,22α,26-tetrol-1-O-α-L-rhamnopyranosyl-(1 → 2)-[β-d-xylopyranosyl-(1 → 3)]-α-l-arabinopyranoside 6 were isolated from the aerial parts of Sansevieria cylindrica. The structures of the new compounds were established by UV, IR, EI-MS, HR-ESI–MS as well as 1D (¹H,¹³C and DEPT-135) and 2D (HSQC, HMBC and TOCSY) NMR spectral analysis. The isolated compounds 1-6 were assayed for in vitro cytotoxicities against the three human tumor cell lines HT116, MCF7 and HepG2. Compound 1 showed a moderate cytotoxicity against MCF7. Compounds 2, 3 and 6 exhibited moderate cytotoxicities against the three used cell lines and compound 5 showed marked cytotoxicities against all used cell lines.     

Flavonoids and coumarins from Platymiscium praecox

The wood of Platymiscium praecox Mart. (Leguminosae-Lotoideae) contains sitosterol, 4,2′,4′-trihydroxychalcone, (2R)-7-hydroxyflavanone, (±)-7,4′-dihydroxyflavanone, (2S, 3S)-3,7-dihydroxyflavanone, 3,7-dihydroxyflavone, 3,7,4′-trihydroxyflavone, 6,7-dihydroxy-4′-methoxyisoflavone and 6,7-dimethoxycoumarin. It also contains three novel compounds: 7-hydroxy-4-methoxy-5-methylcoumarin, 7-O-glucosyloxy-4-methoxy-5-methylcoumarin and 7-hydroxy-4,8-dimethoxy-5-methylcoumarin.     

Withanolides from Withania aristata and their cytotoxic activity

Seven new withanolides (1-7), along with three known ones (8-10), were isolated from the leaves of Withania aristata. Their structures were elucidated on the basis of spectroscopic analysis, including 2D NMR experiments and spectrometric techniques, and the absolute configuration of 1 and 2 was established by CD analysis. In the search for new cytotoxic compounds from Withania species, the isolated compounds 1-9, along with two derivatives, were assayed for their cytotoxicity against HeLa, MCF-7 and A-549 human tumor cell lines. Derivative (4S,20R,22R)-27-acetoxy-4-p-bromobenzoyloxy-1-oxo-witha-2,5,16,24-tetraenolide (13) showed cytotoxicity against all the cell lines assayed with IC₅₀ values ranging from 2.8 to 3.6 μM, and (4S,20R,22R)-4,27-diacetoxy-4-hydroxy-1-oxo-witha-2,5,16,24-tetraenolide (12) exhibited an IC₅₀ value of 5.4 μM on the MCF-7 cell line.     

Inhibition of peroxynitrite-mediated DNA strand cleavage and hydroxyl radical formation by aspirin at pharmacologically relevant concentrations: Implications for cancer intervention

Epidemiological studies have suggested that the long-term use of aspirin is associated with a decreased incidence of human malignancies, especially colorectal cancer. Since accumulating evidence indicates that peroxynitrite is critically involved in multistage carcinogenesis, this study was undertaken to investigate the ability of aspirin to inhibit peroxynitrite-mediated DNA damage. Peroxynitrite and its generator 3-morpholinosydnonimine (SIN-1) were used to cause DNA strand breaks in φX-174 plasmid DNA. We demonstrated that the presence of aspirin at concentrations (0.25-2 mM) compatible with amounts in plasma during chronic anti-inflammatory therapy resulted in a significant inhibition of DNA cleavage induced by both peroxynitrite and SIN-1. Moreover, the consumption of oxygen caused by 250 μM SIN-1 was found to be decreased in the presence of aspirin, indicating that aspirin might affect the auto-oxidation of SIN-1. Furthermore, EPR spectroscopy using 5,5-dimethylpyrroline-N-oxide (DMPO) as a spin trap demonstrated the formation of DMPO-hydroxyl radical adduct (DMPO-OH) from authentic peroxynitrite, and that aspirin at 0.25-2 mM potently diminished the radical adduct formation in a concentration-dependent manner. Taken together, these results demonstrate for the first time that aspirin at pharmacologically relevant concentrations can inhibit peroxynitrite-mediated DNA strand breakage and hydroxyl radical formation. These results may have implications for cancer intervention by aspirin.     

Synthesis of anomeric sulfonamides and their behaviour under radical-mediated bromination conditions

O-Peracetylated methyl 3-(d-glycopyranosylthio)propanoates of β-d-gluco, and α- and β-d-galacto configurations were oxidized to the corresponding S,S-dioxides (sulfones) by Oxone^® or MCPBA. Oxidation of the β-d-gluco derivative with H₂O₂/Na₂WO₄ gave the corresponding S-oxide (sulfoxide). DBU-induced elimination of methyl acrylate from the β-d-gluco and β-d-galacto configured S,S-dioxides (sulfones) gave O-peracetylated β-d-glycopyranosyl-1-C-sulfinates which, on treatment with H₂NOSO₃H, furnished the corresponding β-d-glycopyranosyl-1-C-sulfonamides. Radical-mediated bromination of the protected methyl 3-(β-d-glycopyranosylthio)propanoate S,S-dioxides gave mixtures of 1-C- and 5-C-bromoglycosyl compounds. Similar brominations of the O-peracetylated β-d-glycopyranosyl-1-C-sulfonamides resulted in the formation of α-d-glycopyranosyl bromides and 1-C- and 5-C-bromoglycosyl sulfonamides. A rationale for these observations was proposed. Methyl 3-(β-d-glucopyranosylthio)propanoate, its S,S-dioxide, and β-d-glucopyranosyl-1-C-sulfonamide proved inefficient when tested as inhibitors of rabbit muscle glycogen phosphorylase b.     

Synthesis and antitubercular evaluation of amidoalkyl dibenzofuranols and 1H-benzo[2,3]benzofuro[4,5-e][1,3]oxazin-3(2H)-ones

A new class of amidoalkyl dibenzofuranols and 1H-benzo[2,3]benzofuro[4,5-e][1,3]oxazin-3(2H)-ones was synthesized in very good yields through polyphosphoric acid supported on silica (PPA-SiO₂) catalyzed one-pot three component condensation of 2-dibenzofuranol; aromatic aldehydes and acetamide or benzamide or urea under solvent free conditions. At 125 °C the reaction led to the formation of amidoalkyl dibenzofuranols 5a-k where as at 160 °C cyclization take place to give oxazin-3(2H)-one analogues 6a-e. Screening all the 16 compounds for in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv (MTB) resulted 1-((4-chlorophenyl)(2-hydroxydibenzo[b,d]furanyl)methyl)urea 5h; 1-((4-bromophenyl)(2-hydroxydibenzo[b,d]furanyl)methyl)urea 5i; 1-phenyl-1H-benzo[2,3]benzo furo[4,5-e][1,3]oxazin-3(2H)-one 6a (MIC 3.13 μg/mL) and 1-(4-chlorophenyl)-1H-benzo[2,3]benzofuro[4,5-e][1,3]oxazin-3(2H)-one 6b; 1-(4-bromophenyl)-1H-benzo[2,3]benzofuro [4,5-e][1,3]oxazin-3(2H)-one 6c (MIC 1.56 μg/mL) as most active antitubercular agents.