Noncovalent DNA binding drives DNA alkylation by leinamycin: evidence that the Z,E-5-(thiazol-4-yl)-penta-2,4-dienone moiety of the natural product serves as an atypical DNA intercalator.

Molecular recognition and chemical modification of DNA are important in medicinal chemistry, toxicology, and biotechnology. Historically, natural products have revealed many interesting and unexpected mechanisms for noncovalent DNA binding and covalent DNA modification. The studies reported here characterize the molecular mechanisms underlying the efficient alkylation of duplex DNA by the Streptomyces-derived natural product leinamycin. Previous studies suggested that alkylation of duplex DNA by activated leinamycin (2) is driven by noncovalent association of the natural product with the double helix. This is striking because leinamycin does not contain a classical noncovalent DNA-binding motif, such as an intercalating unit, a groove binder, or a polycation. The experiments described here provide evidence that leinamycin is an atypical DNA-intercalating agent. A competition binding assay involving daunomycin-mediated inhibition of DNA alkylation by leinamycin provided evidence that activated leinamycin binds to duplex DNA with an apparent binding constant of approximately 4.3 ± 0.4 × 10(3) M(-1). Activated leinamycin caused duplex unwinding and hydrodynamic changes in DNA-containing solutions that are indicative of DNA intercalation. Characterization of the reaction of activated leinamycin with palindromic duplexes containing 5'-CG and 5'-GC target sites, bulge-containing duplexes, and 5-methylcytosine-containing duplexes provided evidence regarding the orientation of leinamycin with respect to target guanine residues. The data allow construction of a model for the leinamycin-DNA complex suggesting how a modest DNA-binding constant combines with proper positioning of the natural product to drive efficient alkylation of guanine residues in the major groove of duplex DNA.

Upregulation of endogenous glutathione system by 3H-1,2-dithiole-3-thione in pancreatic RINm5F beta-cells as a novel strategy for protecting against oxidative beta-cell injury.

This study was undertaken to investigate the inducibility of glutathione (GSH), glutathione reductase (GR) and glutathione peroxidase (GPx) by 3H-1,2-dithiole-3-thione (D3T) in beta-cells, and the resultant cytoprotection against oxidant injury. Incubation of the insulin-secreting RINm5F cells with D3T led to significant induction of GSH, GR and GPx. D3T-mediated induction of GSH was abolished by buthionine sulfoximine (BSO), suggesting a critical involvement of gamma-glutamylcysteine ligase (gammaGCL). Consistently, incubation of RINm5F cells with D3T resulted in increased expression of gammaGCL protein and mRNA. Pretreatment of RINm5F cells with D3T provided remarkable protection against oxidant-elicited cytotoxicity. On the other hand, depletion of cellular GSH by BSO sensitized RINm5F cells to oxidant injury. Furthermore, cotreatment of RINm5F cells with BSO to reverse D3T-mediated GSH induction abolished the cytoprotective effects of D3T on oxidant injury. Taken together, this study demonstrates that upregulation of glutathione system by D3T is effective for protecting against oxidative beta-cell injury.

Highly enantioselective Biginelli reaction using a new chiral ytterbium catalyst: asymmetric synthesis of dihydropyrimidines.

The highly enantioselective three-component Biginelli condensation catalyzed by a recyclable chiral ytterbium triflate with a novel hexadentate amine phenol ligand containing a pyridyl group has been developed. A wide range of optically active dihydropyrimidines with remarkable pharmacological interest was obtained in high yields with good to excellent enantioselectivities under mild conditions.

Learning and memory impairment in albino rats after potassium ethylxanthogenate. Effects of nootropic agents.

The effects of the nootropic agents piracetam, aniracetam, meclofenoxate and fipexide on the cognitive functions impaired after potassium ethylxanthogenate, inhibitor of dopamine-beta-hydroxylase, were tested in experiments on albino rats. The changes in learning and memory were traced by the active conditioned avoidance method with negative reinforcement (shuttle-box) and the passive avoidance method (step-down). Potassium ethylxanthogenate, injected intraperitoneally in a dose of 100 mg/kg, markedly impaired learning and memory with both methods used. Piracetam (600 mg/kg), aniracetam (50 mg/kg), meclofenoxate (100 mg/kg) and fipexide (10 mg/kg), administered orally five days before and five days during shuttle-box training, as well as five days before step-down training, completely prevented the impairing effect of potassium ethylxanthogenate on the cognitive processes. The role of the noradrenergic neurotransmitter system and of other brain transmitter systems for memory disturbances caused by potassium ethylxanthogenate, as well as the protective effect of the nootropic drugs used, are discussed.