Regioselective 2′/3′-O-Allylation of Pyrimidine Ribonucleosides Using Phase Transfer Catalysis

Abstract

A short and convenient procedure for regiospecific O-allylation of uridine is reported by employing dibutyltin oxide as a mild base in conjunction with a phase transfer catalyst tetrabutylammonium bromide. The resulting isomeric 2′/3′-O-allyl uridines were separated after conversion into their corresponding 5′-O-DMT derivatives. The 2′-O-allyluridine 3 was then transformed into 2′-O-allylcytidine 7 and both were individually converted into the corresponding β-cyanoethyl phosphoramidite monomers (9 and 10) and a phosphodiester monomer 11, required for oligonucleotide assembly. The utility of 11 is demonstrated by synthesis and characterization of a 2′-O-allyl ribodinucleotide UpU.     

Organotin-induced hemolysis,shape transformation and intramembranous aggregates in human erythrocytes

Organotin compounds examined in this study exhibited a relative order of potency for induction of in vitro hemolysis in human erythrocytes as follows: tri-n-butyltin > tri-n propyltin > tetra-n-butyltin > triphenyltin chloride > tri-n-ethyltin bromide > dibutyltin dichloride > stannous chloride > tri-n-methyltin chloride = butyltin chloride dihydroxide. All of the organotin compounds induced erythrocyte shape transformation from the normal discocyte to an echinocyte and, in addition, triphenyltin chloride, tetra-n-butyltin and tri-n-ethyltin bromide also elicited stomatocyte formation at higher concentrations. Select organotin compounds also formed tin-containing aggregates within the plasma membrane. The relative order of effectiveness for organotin induction of intramembranous aggregates was tri-n-butyltin > tri-npropyltin > tetra-n-butyltin > tri-n-ethyltin bromide, which was based upon the lowest concentration at which they were observed. These results support the previously suggested theory that organotins are membrane effectors because of their comparatively high hydrophobic, lipid partitioning properties. The relatively lipophilic compound, triphenyltin chloride, appeared to be anomalous because it did not readily promote hemolysis or induce the formation of intramembranous aggregates in human erythrocytes. A log-linear statistical model demonstrated an association of hemolysis with both tri-n-butyltin aggregate formation and shape transformation. Select organotin compounds should be useful probes in membrane studies because of their numerous effects.Abbreviations DBT dibutylin dichloride - MBT butyltinchloride dihydroxide - SnCl₂ stannous chloride - TBT tri-n-butyltin - TET tri-n-ethyltin bromide - TMT tri-n-methyltin chloride - TPhT triphenyltin chloride - TPT tri-n-propyltin - TTBT tetra-n-butyltin     

ESIMS and NMR studies on the selective deprotection of acetylated glucosides by dibutyltin oxide

The reaction process for the selective deprotection of acetylated glucosides by dibutyltin oxide in methanol is investigated by using methyl 2,3,4,6-tetra-O-acetyl-α-d-glucopyranoside as a model substrate with ESIMS and NMR techniques. According to the results, it is inferred that at first, dimeric 1,3-dimethoxytetrabutyldistannoxane is formed by the reaction of dibutyltin oxide with methanol, and then the tetraorganodistannoxane reacts with the acetylated glucoside to produce glucoside–organotin complex intermediates. Finally, the complex intermediates are hydrolyzed leading to the free-OH glucoside and organotin acetate derivatives. The reaction is affected by neighboring group participation and steric hindrance, which allow for high selectivities among different acetyl groups in acetylated glucosides.     

Deciphering mechanistic implications of antimicrobial and antioxidant potentials of certain new dibutyltin(IV) formulations as possible therapeutic options based on DFT and hybrid materials paradigm

Mechanistic implications of antimicrobial and in vitro antioxidant potentials of a set of newly generated nonbridged mononuclear N,O-orthometallated and carboxylate bridged binuclear nonorthometallated dibutyltin(IV) formulations have been investigated. Some of these formulations were screened for their antibacterial and antifungal activities against Escherichia coli and Candida albicans, respectively whereas in vitro antioxidant potential was examined by Ferric reducing antioxidant power (FRAP) assay. Nonbridged mononuclear N,O-orthometallated dibutyltin(IV) formulations were generated by the reactions of Bu₂SnCl₂ with sodium salts of 2-aminophenol/substituted 2-aminophenol and flexible N-protected amino acids in 1:1:1 molar ratio in refluxing dry THF. Plausible structures of these nonbridged mononuclear N,O-orthometallated dibutyltin(IV) formulations containing flexible N-protected amino acids have been suggested on the basis of spectroscopic and mass studies of some representative formulations. Plausible structures suggested on the basis of spectroscopic studies are corroborated by density functional theory (DFT/B3LYP method) (SPARTAN-20) investigation of a representative dibutyltin(IV) complex and the ligands involved in it. The presence of two different classes of organic ligands in this complex provides an opportunity to study optimized topologies, bonding, distortions, optimized energy, and stability of the complex.     

Degradation of tributyltin by the filamentous fungus Cunninghamella elegans, with involvement of cytochrome P-450

Cunninghamella elegans degraded tributyltin (TBT) at 20 mg l^–1 when grown in Sabouraud medium. Above this concentration, growth was inhibited. After 7 d 70% TBT (added at 10 mg l^–1) was converted to less toxic derivatives: dibutyltin and monobutyltin. TBT metabolism was totally blocked by cytochrome P-450 inhibitors, metyrapone and proadifen. Only in medium with 1-aminobenzotriazole, was dibutyltin (0.42 mg l^–1) found after 7 d of culturing. It is postulated that the significant resistance of C. elegans to TBT is associated with the capacity of the fungus to metabolise TBT.     

A mild and selective method for cleavage of O-acetyl groups with dibutyltin oxide

A mild and efficient neutral method for the cleavage of O-acetyl groups with dibutyltin oxide has been developed. This method is especially useful in the synthesis of glycosides containing base- or acid-sensitive multifunctional groups.     

Enhanced adhesion and chemoattraction of zoospores of the fouling alga enteromorpha to some foul‐release silicone elastomers

Significantly higher numbers of zoospores of the fouling, green alga Enteromorpha adhered to silicone elastomers cured by dibutyltin dilaurate (DBTDL) than to identical polymers cured by dibutyltin diacetate (DBTDA). Enhanced zoospore adhesion was shown to be due to the presence of DBTDL and the effect was concentration‐dependent. Further experiments revealed that enhanced zoospore adhesion also occurred to glass coverslips coated with lauric acid (C₁₂) and other saturated fatty acids. The possibility that fatty acids may act as chemical cues (chemoattractants), guiding motile zoospores to the substratum for settlement in the natural environment is discussed. Settlement of other fouling organisms to DBTDL‐cured silicone elastomers is currently being investigated.     

Effective methods for enantioselective analysis of glycidol derivatives by liquid chromatography

Methodology for determination of the enantiomeric purity of sixteen 2,3-epoxy-1-propanols (glycidols) is delineated. Conversion of these epoxy alcohols and 1-naphthyl isocyanate (NIC) into the 1-naphthyl carbamates is catalyzed by dibutyltin diacetate. Enantiomers of these carbamates are resolved on a Chiralcel® OD column. Advantages of this method include mildness of reaction conditions, nonreliance on diastereomeric derivatization, and appendage of a UV-absorbing chromophore to the analyte.     

Metabolism of bromide and its interference with the metabolism of iodine

The present knowledge about the metabolism of bromide with respect to its goitrogenic effects, including some conclusions drawn from our recent research on this subject, is reviewed. Firstly, the biological behavior of bromide ion is compared with that of chloride and iodide. Secondly, the details about distribution and kinetics of bromide ions in the body and in 15 different organs and tissues of the rat are given. Significant correlation between the values of the steady-state concentration of bromide in the respective tissue and of the corresponding biological half-life was found in most tissues examined. A remarkably high concentration of radiobromide was found in the skin, which represents, due to its large mass, the most abundant depot of bromide in the body of the rat. Thirdly, the effects of excessive bromide on the rat thyroid are summarized, along with the interference of exogenous bromide with the whole-body metabolism of iodine. It is suggested that high levels of bromide in the organism of experimental animals can influence their iodine metabolism in two parallel ways: by a decrease in iodide accumulation in the thyroid and skin (and in the mammary glands in lactating dams), and by a rise in iodide excretion by kidneys. By accelerating the renal excretion of iodide, excessive bromide can also influence the pool of exchangeable iodide in the thyroid. Finally, our recent results concerning the influence of high bromide intake in the lactating rat dam on iodine and bromide transfer to the suckling, and the impact of seriously decreased iodine content and increased bromide concentration in mother's milk on the young are discussed. We must state, however, that the virtue of the toxic effects of excessive bromide on the thyroid gland and its interference with the biosynthesis of thyroid hormones, as well as the exact mechanism of bromide interference with postnatal developmental processes remains to be elucidated.     

Physico-chemical and antimicrobial properties and the shelf life of experimental endodontic sealers containing metal methacrylates

Abstract

The objective of this study was to evaluate the physico-chemical and antimicrobial properties of a dual polymerization experimental endodontic sealer (E) and experimental sealers containing dibutyltin methacrylate (Sn²⁺) (ETs) or calcium methacrylate (Ca²⁺) (ECs). The pH and ion release levels of the sealers were measured. The dimensional stability was evaluated in accordance with ISO 6876. Biofilm growth inhibition was evaluated using confocal laser scanning microscopy (CLSM). Biofilm viability analysis was performed using the SYTO 9 technique. The shelf life was evaluated through the degree of conversion and film thickness tests after the sealers had been stored for different periods of time. For statistical analysis, ANOVA and Tukey’s post hoc test were used, with a significance level of 5%. ETs revealed better anti-biofilm potential after 15?days than that of the controls. The degree of conversion was reduced after the shelf-life period. The addition of calcium and dibutyltin methacrylate improved the anti-biofilm properties of the experimental endodontic sealer without impairing their physico-chemical properties.     

An improved method for the preparation of 3-O-benzyl-6-O-pivaloyl-alpha-D-glucopyranose 1,2,4-orthopivalate

The synthetic route to 3-O-benzyl-6-O-pivaloyl-alpha-D-glucopyranose 1,2,4-orthopivalate (1), which was previously established, was shortened by introducing two novel reactions, regioselective pivaloylation with dibutyltin oxide in toluene for the regioselective activation of hydroxyl groups, and intramolecular orthoesterification with benzenesulfonyl chloride and triethylamine in dichloromethane. Compound 1 was obtained in 58.8% overall yield from commercially available 1,2:5,6-di-O-isopropylidene-alpha-D-glucopyranose (2) via four reaction steps.     

Tiotropium bromide (Ba 679 BR), a novel long-acting muscarinic antagonist for the treatment of obstructive airways disease

Tiotropium bromide (Ba 679 BR) is a novel potent and long-lasting muscarinic antagonist that has been developed for the treatment of chronic obstructive airways disease (COPD). Binding studies with [3H]tiotropium bromide in human lung have confirmed that this is a potent muscarinic antagonist with equal affinity for M1-, M2- and M3-receptors and is approximately 10-fold more potent than ipratropium bromide. Tiotropium bromide dissociates very slowly from lung muscarinic receptors compared with ipratropium bromide. In vitro tiotropium bromide has a potent inhibitory effect against cholinergic nerve-induced contraction of guinea-pig and human airways, that has a slower onset than atropine or ipratropium bromide. After washout, however, tiotropium bromide dissociates extremely slowly compared with the dissociation of atropine and ipratropium bromide. Measurement of acetylcholine (ACh) release from guinea-pig trachea shows that tiotropium bromide, ipratropium bromide and atropine all increase ACh release on neural stimulation and that this effect is washed out equally quickly for the three antagonists. This confirms binding studies to transfected human muscarinic receptors which suggested that tiotropium bromide dissociates slowly from M3-receptors (on airway smooth muscle) but rapidly from M2 autoreceptors (on cholinergic nerve terminals). Clinical studies with inhaled tiotropium bromide confirm that it is a potent and long-lasting bronchodilator in COPD and asthma. Furthermore, it protects against cholinergic bronchoconstriction for > 24 h. This suggests that tiotropium bromide will be a useful bronchodilator, particularly in patients with COPD, and may be suitable for daily dosing. The selectivity for M3- over M2-receptors may also confer a clinical advantage.     

The intermolecular migration of polyol stannylenes as a reaction contributing to the regioselectivity of substitution

Pairs of the partially protected glycosides benzyl 4,6-O-benzylidene-beta-D-galactopyranoside, benzyl 2,3-di-O-benzyl-beta-D-galactopyranoside, benzyl 2,6-di-O-benzyl-alpha-D-galactopyranoside, and benzyl 2,3-di-O-benzyl-alpha-D-glucopyranoside were treated with equimolar proportions of Bu2SnO in benzene in the conditions of stannylene formation, and the resulting mixture was benzoylated in situ with benzoyl chloride. Estimation of the product of benzoylation led to the following order of reactivity in the stannylenation reaction: 2,3-diol > 4,6-diol, and 2,3-diol > 3,4-diol. An intermolecular migration of dibutyltin between sugars was demonstrated. It is considered that these migrations contribute efficiently to the regiospecificity of the stannylene reaction.     

Soil fumigation with methyl bromide: the phytotoxicity of inorganic bromide to carnation plants

Rooted carnation cuttings often developed phytotoxic symptoms when planted in soil previously fumigated with methyl bromide, and many died. Those which recovered suffered a marked check in growth and flower production was reduced. Plant injury and effects on flower yield were more severe at high rates of fumigant application, but were reduced by flooding the soil with water or by incorporating peat into the growing medium.
Plant survival and flower yield were inversely related to the concentration in soil of inorganic bromide formed by the breakdown of the fumigant. Injury to plants occasionally occurred in the presence of soil concentrations of inorganic bromide as low as 5 pglg. Flooding the soil or incorporating peat into it were beneficial because these treatments reduced the soil concentration of inorganic bromide.
Carnation plants which were grown in soil previously fumigated with methyl bromide or supplemented directly with potassium bromide accumulated bromide in their leaves, and a bromide gradient was eventually established, the concentrations decreasing from the bottom to the top of the plants.
The evidence that inorganic bromide is the cause of the injury to carnations is discussed, and the role of peat in alleviating the incidence and seventy of the injury is considered.     

Reaction of 2'-deoxycytidine with peroxynitrite in the presence of ammonium bromide

Peroxynitrite, a reactive nitrogen species generated from nitric oxide and superoxide anion radical, is an endogenous potential risk factor for human cancer. When 2′-deoxycytidine was incubated with peroxynitrite at neutral pH and 37 °C, the reaction was greatly enhanced by the addition of ammonium bromide. Both ammonium ion and bromide ion were required to exert the enhancing effect. In addition to ammonium ion, methylamine and dimethylamine exerted the enhancing effect in the presence of bromide ion. Two major products were identified as 5-hydroxy-2′-deoxycytidine and 5-bromo-2′-deoxycytidine. Hypochlorite solution and bromine water reacted with 2′-deoxycytidine generating 5-hydroxy-2′-deoxycytidine and 5-bromo-2′-deoxycytidine in the presence of ammonium bromide with the yields similar to those of the reaction of peroxynitrite with ammonium bromide. Fenton reaction of 2′-deoxycytidine was suppressed by the addition of ammonium bromide. Nitrogen dioxide gas did not react with 2′-deoxycytidine in the presence or the absence of ammonium bromide. These results suggest that in the presence of ammonium ion or amines, bromide ion interacts with peroxynitrous acid, which is a protonated form of peroxynitrite, but not with hydroxyl radical or nitrogen dioxide generated by homolysis of peroxynitrous acid, to form hypobromous acid. In the presence of ammonium ion or amines, bromide ion may play a role in enhancing the genotoxic effects of peroxynitrite in humans.     

The metabolic effects and uptake of ethidium bromide by rat liver mitochondria.

The uptake of ethidium bromide by rat liver mitochondria and its effect on mitochondria, submitochondrial particles, and F₁ were studied. Ethidium bromide inhibited the State 4-State 3 transition with glutamate or succinate as substrates. With glutamate, ethidium bromide did not affect State 4 respiration, but with succinate it induced maximal release of respiration. These effects appear to depend on the uptake and concentration of the dye within the mitochondrion. In submitochondrial particles, the aerobic oxidation of NADH is much more sensitive to ethidium bromide than that of succinate. Ethidium bromide partially inhibited the ATPase activity of submitochondrial particles and of a soluble F₁ preparation. Ethidium bromide behaves as a lipophilic cation which is concentrated through an energy-dependent process within the mitochondria, producing its effects at different levels of mitochondrial function. The ability of mitochondria to concentrate ethidium bromide may be involved in the selectivity of the dye as a mitochondrial mutagen.     

Tests of dibutyltin compounds as potato blight fungicides

Dibutyltin dicarboxylates were about one-tenth as effective as fentin acetate in controlling potato haulm blight (Phytophthora infestans) in laboratory tests on detached leaflets, but were less phytotoxic. Tributyltin acetate was no more effective than dibutyltin diacetate; dioctyltin dichloride was ineffective.     

Eosinophils preferentially use bromide to generate halogenating agents

Human eosinophils preferentially utilize bromide to generate a brominating agent, even at physiological halide concentrations, where chloride (140 mM) is over 1000-fold greater than bromide (20-100 microM). Under the same conditions, neutrophils use chloride to generate a chlorinating agent. The total amount of active halogen trapped by 1,3,5-trimethoxybenzene from eosinophils increases by over 2-fold as the added bromide concentration increases from 0 to 100 microM, with approximately 40 nmol of halogen trapped per million cells at the highest bromide level. At least 25-35% of the oxygen consumed by stimulated eosinophils is directed toward the generation of halogenating species. Since the relative halogenating behavior of eosinophil peroxidase and neutrophil myeloperoxidase in this bromide range is essentially identical to that of the cells, the specificity of eosinophils toward bromide is intrinsic to eosinophil peroxidase and not to any special cellular properties. These results suggest that human eosinophils use bromide in vivo and that a deficiency of bromide may influence their ability to produce halogenating agents.     

Influence of ethidium bromide on hyperthermic modification of bleomycin-DNA interaction

The effect of hyperthermic treatment on the binding of 59Fe-labeled bleomycin to DNA has been studied. Enhanced binding was observed at elevated temperatures. The influence of the DNA-intercalating agent, ethidium bromide, on bleomycin-DNA interaction was also studied and revealed a considerable decrease in this interaction at ethidium bromide levels below 1 microgram/ml. Ethidium bromide was observed to remove the enhanced bleomycin-DNA interaction recorded previously following incubation at hyperthermic temperatures. Synergistic action of bleomycin and hyperthermia on loss of clonogenic ability of HT29R cells is reported. Incubation of cells under hyperthermic conditions with bleomycin in the presence of ethidium bromide removes this synergism, producing a less than additive effect for the action of bleomycin and heat after ethidium bromide effects are taken into account.     

Permeability of the membrane of the Escherichia coli envelope for ethidium bromide

The interaction of ethidium bromide, a fluorescent dye, with Escherichia coli cells was studied. The envelope of intact cells was shown to be impermeable for ethidium bromide molecules. The dye penetrated however into E. coli spheroplasts. The barrier properties of the cell envelope against ethidium bromide were ruptured if the cells were treated with EDTA. The results suggest that the outer membrane serves as a principal barrier against penetration of ethidium bromide inside the cells while the cytoplasmic membrane of E. coli is permeable for the dye.