Preparation, reactivity, and neurotoxicity of tryptamine-4,5-dione

Quantum-dot/dopamine bioconjugates function as redox coupled assemblies for in vitro and intracellular pH sensing

The use of semiconductor quantum dots (QDs) for bioimaging and sensing has progressively matured over the past decade. QDs are highly sensitive to charge-transfer processes, which can alter their optical properties. Here, we demonstrate that QD-dopamine-peptide bioconjugates can function as charge-transfer coupled pH sensors. Dopamine is normally characterized by two intrinsic redox properties: a Nernstian dependence of formal potential on pH and oxidation of hydroquinone to quinone by O(2) at basic pH. We show that the latter quinone can function as an electron acceptor quenching QD photoluminescence in a manner that depends directly on pH. We characterize the pH-dependent QD quenching using both electrochemistry and spectroscopy. QD-dopamine conjugates were also used as pH sensors that measured changes in cytoplasmic pH as cells underwent drug-induced alkalosis. A detailed mechanism describing the QD quenching processes that is consistent with dopamine's inherent redox chemistry is presented.

Synthesis and evaluation of calystegine B2 analogues as glycosidase inhibitors

A practical synthesis of polyhydroxylated 6-oxa-nor-tropanes incorporating the essential structural features of calystegine B(2) from 5-deoxy-5-thioureido and 5-ureido-L-idofuranose precursors is presented. The methodology relies on the ability of pseudoamide-type nitrogen atoms (thiourea, urea, and carbamate) to undergo nucleophilic addition to the masked aldehyde group of the monosaccharide. The generated hemiaminal functionality may further undergo in situ intramolecular glycosidation to give the bicyclic aminoacetal compounds, the whole process being favored by the anomeric effect. A series of derivatives bearing different substituents at nitrogen has been prepared and screened against several glycosidases in comparison with xylonojirimycin-type piperidine analogues. Interestingly, strong and highly specific inhibition of bovine liver beta-glucosidase was observed for 6-oxacalystegine B(2) analogues incorporating aromatic pseudoaglyconic groups. On the basis of these data, a 1-azasugar inhibition mode is proposed for this family of glycomimetics.

The chemistry of indoles. CIII. Simple syntheses of serotonin, N-methylserotonin, bufotenine, 5-methoxy-N-methyltryptamine, bufobutanoic acid, N-(indol-3-yl)methyl-5-methoxy-N-methyltryptamine, and lespedamine based on 1-hydroxyindole chemistry

Application of regioselective nucleophilic substitution reactions of 1-hydroxytryptamines to novel and simple syntheses of serotonin (1a), N-methylserotonin (1b), bufotenine (1c), 5-methoxy-N-methyltryptamine (2a), bufobutanoic acid (3a), N-(indol-3-yl)methyl-5-methoxy-N-methyltryptamine (4), and lespedamine (5) are described. Effective syntheses of 5-benzyloxytryptamine and 1-methoxy-2-oxindoles are also reported.

Chemical and biological properties of 5-indolones

Indolones of the general formula 1 (Fig. 1 and 2) can act as Michael substrates, which readily add various nucleophiles. 1,4-Addition of S-nucleophiles to these indolones gives access to compounds of the general formula 2 (Fig. 2). The addition is reversible, meaning that these compounds behave as prodrugs of the (in-vitro) cytotoxic indolones. The addition products possess less cytotoxicity of their own, but can presumably release the parent indolones in-vivo. This behaviour makes them valuable compounds, allowing their use as cytotoxic agents. Furthermore, some of the addition products possess antibiotic activity, making them worth testing as agents against certain microbes. Their specificity towards certain microorganisms, which does not fit the usual scheme of activity towards gram positive or gram negative bacteria, is remarkable and needs further verification.

Neurotoxicity of free-radical-mediated serotonin neurotoxin in cultured embryonic chick brain neurons

Exposure of serotonin (5-HT) to oxygen-derived free-radical-generating system, xanthine oxidase-hypoxanthine or to a Fenton reaction results in the formation of the neurotoxin, tryptamine-4,5-dione. In cultured embryonic chick brain neurons, incubation of tryptamine-4,5-dione or its ethyl carbonate derivative resulted in a dose-dependent neurotoxicity (1-100 microM). The addition of sulfhydryl compound, glutathione at 2 or 10 microM significantly enhanced the toxicity induced by 10 microM tryptamine-4,5-dione. On the contrary, glutathione at 10 microM decreased the neurotoxic effect caused by 10 microM 5,6- and 5,7-dihydroxytryptamine in the cultured neurons. The toxicity resulted from 5,6- and 5,7-dihydroxytryptamine could be fully prevented by a 5-HT uptake inhibitor, fluoxetine. However, the toxicity caused by tryptamine-4,5-dione and glutathione conjugate could not be blocked by fluoxetine (10 or 100 microM) or by a glutathione transferase inhibitor, boric acid/serine. The results indicate a different molecular mechanism among 5-HT derived neurotoxins and suggest that tryptamine-4,5-dione and/or its glutathione conjugate would cause neuronal damage, if they are formed in vivo.

[2-Amino-3-cyano-dihydroindol-5-ones. 2. The biological activity of a new class of compounds]

2-Amino-3-cyano-dihydroindol-5-ones 2 and 3 are formed by reaction of 2-Aminopyrrole-3-carbonitriles 1 with acetylenic acid esters. In various biological test systems they behave as cytotoxic agents.

[2-Amino-3-cyano-dihydroindol-5-ones. 3. The chemical reactivity of a new class of compounds]

The chemical reactivity of cytotoxic 5-indolone derivatives is examined in order to get ideas about their behaviour in biological systems. Dienone-phenol-rearrangement preserving the indole ring system could not be achieved, aromatization of 1b gives the phenol derivative 3 alpha. In diluted NaOH ester hydrolysis occurs (1a,b----4a,b). Hydrolysis in conc. H2SO4 yields the amides 5a,b,d. In ethanolic HCl the ammonium salts 6a,b,d are formed. Acylation of 1a to 8 reveals the endocyclic N-atom as the nucleophilic center. Benzaldehyde being a strong electrophile adds to 1b in position 4. Weaker electrophiles such as dimethyl acetylenedicarboxylate (ADC) only react with the amides 5b,d to give 11 and 12. Nucleophiles (water, ethanol, n-propylamine) add to the delta 6-double bond yielding 14-16.