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PubMed1990

Synthesis and in vitro evaluation of some modified 4-thiopyrimidine nucleosides for prevention or reversal of AIDS-associated neurological disorders.

Oxygen-sulfur exchange at the C-4 carbonyl of several modified pyrimidine nucleosides, including 3'-azido-3'-deoxythymidine (AZT), is described in an effort to enhance the lipophilicity and, thereby, the delivery to the central nervous system of the sulfur analogues without compromising the anti-HIV activities of the parental structures. Preparation of 3'-azido-3'-deoxy-4-thiothymidine (3) proceeded from 4-thiothymidine (1) and utilized the same methodology developed for the initial synthesis of AZT. Thiation of 2',3'-didehydro-3'-deoxythymidine (4a) and 2',3'-didehydro-2',3'-dideoxyuridine (4c) was carried out with Lawesson's reagent on the corresponding 5'-O-benzoate esters, 4b and 4d, to give 5a and 5c, respectively. The latter, on alkaline hydrolysis, gave 2',3'-didehydro-3'-deoxy-4-thiothymidine (5b) and 2',3'-didehydro-2',3'-dideoxyuridine (5d), respectively. The same series of reactions were applied to the 5'-O-benzoate esters of 2',3'-dideoxyuridine (6a) and 3'-deoxythymidine (6b) to give 2',3'-dideoxy-4-thiouridine (7d) and 3'-deoxy-4-thiothymidine (7b), respectively. Characterization of the saturated and unsaturated thionucleosides included mass spectrometric studies. Under electron impact conditions, the thiated analogues gave more intense parent ions than the corresponding oxygen precursors. The lipophilicity of thymidine and the 3'-deoxythymidine derivatives are enhanced significantly, as indicated, by increases in corresponding P values (1-octanol-0.1 M sodium phosphate) upon replacement of the 4-carbonyl oxygens by sulfur. Compounds 5b, 5d, 7b, and 7d were evaluated for their effects on HIV-induced cytopathogenicity of MT-2 and CEM cells. Only 5b and 7b were moderately active in protecting both cell lines against the cytolytic effect of HIV. The inhibitory effects of analogues 5b, 5d, 7b, and 7d on thymidine phosphorylation by rabbit thymus thymidine kinase were evaluated. Only 3 showed moderate affinity (Ki = 54 microM) for the enzyme. The generally weak anti-HIV activities of the remaining thio analogues are consistent with correspondingly low susceptibilities to thymidine kinase phosphorylation as estimated from the respective Ki values of the synthetic nucleosides. However, the phosphorylation of the 5'-monophosphate derivatives to their respective 5'-triphosphates must also be considered in connection with the weak in vitro anti-HIV effects of these thiated compounds.

AIDS Dementia Complex↗
PubMed2002

Oxathiaphospholane approach to N- and O-phosphorothioylation of amino acids.

A method of highly efficient synthesis of N- and O-phosphorothioylated amino acids was developed. N- and O-(2-Thiono-1,3,2-oxathiaphospholanyl)amino acid methyl esters (3) were prepared in high yields in reaction of amino acid methyl esters with 2-chloro-1,3,2-oxathiaphospholane in pyridine in the presence of elemental sulfur. Compounds 3 were converted in high yield into the corresponding methyl or benzyl phosphorothioamides 6 and 7 by DBU-assisted treatment with methanol or benzyl alcohol. When 3-hydroxypropionitrile was used instead of methanol or benzyl alcohol, the corresponding 2-cyanoethylphosphorothioamidates 4 were obtained in high yield, from which the 2-cyanoethyl group was removed with concentrated ammonium hydroxide. The oxathiaphospholane methodology was also applied for the phosphorylation of amino acids. Thus, 2-oxo-1,3,2-oxathiaphospholane derivatives 10 were prepared by oxidation of compounds 3 with SeO(2.) Compounds 10 were transformed into the corresponding phosphate diesters or amidoesters upon treatment with 3-hydroxypropionitrile in the presence of DBU. The DBU-assisted oxathiaphospholane ring-opening process in 3 and 10 did not cause any measurable C-racemization of phosphorothioylated/phosphorylated amino acids.

Amino Acids↗
PubMed2006

When ethyl is infinitely different from methyl: double addition of lithiated dithianes to aromatic carboxylates revisited.

Addition of lithiated alkyl dithianes to benzoyl chloride or methyl benzoate does not produce the expected product of double addition, alpha,alpha-bis(alkyldithianyl) benzyl alcohol, for alkyls larger than methyl. Instead, the first step intermediate, i.e. 2-benzoylated dithiane, undergoes an electron-transfer reduction by the second molecule of the dithianyl anion. This reduction is followed by the ring-opening mesolytic fragmentation of the dithiane ring in the ketyl anion radical and subsequent radical recombination yielding acetophenone-tethered thioortho esters 4, alpha-[3-(2-alkyl-1,3-dithiane-2-ylthio)propylthio]-alpha-alkyl-acetophenones. It appears that the Corey-Seebach bisaddition of lithiated dithianes to methyl benzoate is an exception rather than the rule in the alkyl dithiane series.

Carboxylic Acids↗
PubMed2004

Base-catalyzed inversion of chiral sulfur centers. A computational study.

[reaction: see text] A theoretical study on the pyramidal inversion of the chiral sulfur compounds SO(X)(Me) (X = Cl, OMe, p-MePh) has been carried out by means of the DFT(Becke3LYP) method. Our results reveal that in the case of X = Cl, an organic tertiary amine such as NMe(3) can catalyze the racemization. The base-catalyzed inversion of SO(Cl)(Me) is proposed as a feasible dynamic kinetic resolution mechanism for the synthesis of chiral sulfoxides by the DAG method.

Journal Article↗
PubMed2004

Thioglycuronides: synthesis and application in the assembly of acidic oligosaccharides.

[reaction: see text] Partially protected thioglycuronic acids are prepared efficiently by chemo- and regioselective oxidation of the corresponding thioglycosides using the TEMPO/BAIB reagent combination. After esterification, the thioglycuronic acids proved to be useful as both donor and acceptor in sulfonium-mediated condensations toward acidic di- and trisaccharides.

Cyclic N-Oxides↗
PubMed2006

Thionation using fluorous Lawesson's reagent.

[reaction: see text] Thionation of amides, 1,4-diketones, N-(2-oxoalkyl)amides, N,N'-acylhydrazines, and acyl-protected uridines with the use of a fluorous analogue of the Lawesson's reagent leads to thioamides, thiophenes, 1,3-thiazoles, 1,3,4-thiadiazoles, and acyl-protected 4-thiouridines. The isolation of the final products in high yields is achieved in most cases by a simple filtration (fluorous solid-phase extraction).

Combinatorial Chemistry Techniques↗
PubMedDate not supplied

Site-specific DNA damage induced by cobalt(II) ion and hydrogen peroxide: role of singlet oxygen.

The effect of Co(II) ion on the reaction of hydrogen peroxide with DNA was investigated by a DNA sequencing technique using 32P-5'-end-labeled DNA fragments obtained from human c-Ha-ras-1 protooncogene. Co(II) induced strong DNA cleavage in the presence of hydrogen peroxide even without alkali treatment. Guanine residues were the most alkali-labile site, and the extent of cleavages at the positions of thymine and cytosine was dependent on the sequence. Adenine residues were relatively resistive. Diethylenetriaminepentaacetic acid, present in excess over Co(II), inhibited DNA cleavage. Singlet oxygen scavengers (dimethylfuran, sodium azide, 1,4-diazabicyclo[2.2.2]octane, dGMP), sulfur compounds (methional, methionine), and superoxide dismutase inhibited DNA cleavage completely. Hydroxyl radical scavengers were not so effective as singlet oxygen scavengers. ESR studies using 2,2,6,6-tetramethyl-4-piperidone as a singlet oxygen trap suggest that Co(II) reacts with hydrogen peroxide to produce singlet oxygen or its equivalent. ESR studies using 5,5-dimethylpyrroline N-oxide (DMPO) showed that the hydroxyl radical adduct of DMPO was also formed. The results suggest that Co(II) ion binds to DNA and subsequently reacts with hydrogen peroxide to produce singlet oxygen and hydroxyl radicals and that singlet oxygen plays a more important role in the DNA damage than hydroxyl free radicals.

Cloning, Molecular↗
PubMedDate not supplied

Possible role of thioformamide as a proximate toxicant in the nephrotoxicity of thiabendazole and related thiazoles in glutathione-depleted mice: structure-toxicity and metabolic studies.

In mice depleted of GSH by treatment with buthionine sulfoximine (BSO), thiabendazole (TBZ) causes renal injury characterized by an increase in serum urea nitrogen (SUN) concentration and by tubular necrosis. Previous studies have shown that TBZ requires metabolic activation before it produces nephrotoxicity and that the structure contributing to the toxicity of TBZ is the thiazole moiety of the molecule. TBZ and its thiazole analogues were examined for the ability to increase SUN concentration and serum alanine aminotransferase activity in GSH-depleted mice. Unsubstituted thiazole and thiazoles with 4- and/or 5-, and no 2-, substituents caused marked increases in SUN concentration, suggesting nephrotoxicity. Furthermore, the nephrotoxic potency of these thiazoles decreased with the increasing number and bulk of the 4- and/or 5-substituents. On the other hand, the target organ (the kidney or liver) and the toxic potency of 4-methylthiazoles were markedly altered with the type of substituents at the 2-position. These observations and the known toxicity of thiono-sulfur compounds led us to the hypothesis that the nephrotoxic thiazoles, which lack 2-substituents, would undergo microsomal epoxidation of the C-4,5 double bond and, after being hydrolyzed, the resulting epoxide would then be decomposed to form thioformamide, a possibly toxic metabolite. Evidence for this hypothesis was provided by the results that thioformamide and tert-butylglyoxal as the accompanying fragment were identified as urinary metabolites in mice dosed with 4-tert-butylthiazole and that thioformamide caused a marked increase in SUN concentration when administered to mice in combination with BSO.

Alanine Transaminase↗
PubMed2000

Evidence for the involvement of N-methylthiourea, a ring cleavage metabolite, in the hepatotoxicity of methimazole in glutathione-depleted mice: structure-toxicity and metabolic studies.

In mice depleted of GSH by treatment with buthionine sulfoximine (BSO), methimazole (2-mercapto-1-methylimidazole, MMI) causes liver injury characterized by centrilobular necrosis of hepatocytes and an increase in serum alanine transaminase (SALT) activity. MMI requires metabolic activation by both P450 monooxygenase and flavin-containing monooxygenase (FMO) before it produces the hepatotoxicity. MMI and its analogues were examined for the ability to increase SALT activity in GSH-depleted mice. Saturation of the C-4,5 double bond in MMI resulted in a complete loss of hepatotoxicity. Similarly, ring fusion of a benzene nucleus to the C-4,5 double bond, forming 2-mercapto-1-methylbenzimidazole, abolished the toxic potency. As for MMI, 2-mercapto-1,4,5-trimethylimidazole, and 2-mercapto-1-methyl-4, 5-di-n-propylimidazole, the toxic potency decreased with the increasing bulk of the 4- and 5-alkyl substituents. Furthermore, methylation of the thiol group of MMI totally reduced its toxicity. These structural requirements and the known toxicity of thiono-sulfur compounds led us to the hypothesis that MMI would undergo epoxidation of the C-4,5 double bond by P450 enzymes and, after being hydrolyzed, the resulting epoxide would be then decomposed to form N-methylthiourea, a proximate toxicant. Before N-methylthiourea would produce toxicity, it would be further biotransformed to its S-oxidized metabolites mainly by FMO. Evidence for this hypothesis was provided by the facts that N-methylthiourea and glyoxal as the accompanying fragment were identified as urinary metabolites in mice treated with MMI and that N-methylthiourea caused a marked increase in SALT activity when administered to mice in combination with BSO.

Animals↗
PubMed2001

A multifactorial investigation of the ability of oral health care products (OHCPs) to alleviate oral malodour.

UNLABELLED: AIM, BACKGROUND: Oral malodour (halitosis) is generally ascribable to oral microbial putrefaction generating malodorous volatile sulphur compounds which predominantly comprise dihydrogen sulphide and methyl mercaptan. This study assesses the relative effectiveness of 6 oral health care products in reducing oral cavity volatile sulphur compound concentrations. METHOD: A mixed model 3-factor factorial experimental design involving 6 volunteers, 7 treatment regimens (products I-VI* and water placebo) and 5 time-points (0.00-5.29 h) was undertaken. Electron-donating volatile sulphur compound levels were determined in triplicate using a sulphide monitor (Interscan model 1170) both prior to (0.00 h) and following oral rinsing (20 ml of 5 of the products) or chewing (2 capsules of the remaining product) episodes with each product examined (0.29, 1.29, 2.29 and 5.29 h post-administration). RESULTS: Results were recorded as peak and steady-state volatile sulphur compound equivalents (ppb). With the exception of one of the products, each oral health care product tested was found to reproducibly reduce volatile sulphur compound concentrations within 20 min of treatment; the mean % decreases in peak (and corresponding steady-state) levels ranging from 3.6 (0.0) to 16.8 (16.4)%. Subsequently, volatile sulphur compound concentrations returned to their zero-control (baseline) values within 5 h, the rate of this regression being in the reverse of the order observed for the magnitude of the primary 20 min reduction for both peak and steady-state measurements. As expected, the water placebo exerted no influence on oral cavity volatile sulphur compound levels. The most effective oral health care products contained admixtures of chlorite anion and chlorine dioxide (both of these agents have the ability to directly oxidise volatile sulphur compounds to non-malodorous products and the latter is also powerfully cidal towards odourigenic micro-organisms). CONCLUSIONS: We therefore conclude that oral health care products containing such oxohalogen oxidants may provide a useful therapeutic strategy for the treatment of oral malodour.

Adult↗
PubMed2002

Effect of initial periodontal therapy on sulcular/tongue sulfide level. A pilot study.

BACKGROUND: : Volatile sulfur compounds (VSC), such as hydrogen sulfide, methyl mercaptan and dimethyl sulfide, are toxic metabolites produced by periodontal pathogens. These VSC are also released from the tongue dorsum. Currently, limited data are available on how periodontal treatments may affect sulcular/tongue sulfide level. The aim of this study was to determine effect of initial therapy including oral hygiene instruction and scaling and root planing (SRP) on sulcular/tongue sulfide level. METHODS: : Thirteen subjects diagnosed with chronic periodontitis and having three representative periodontal pocket depth (PD) strata in one quadrant (PD or= 7.0 mm: severe disease sites) were selected. Clinical periodontal parameters were recorded at baseline and 3 weeks after completion of the initial therapy. The sulfide levels in three representative periodontal pockets (pS) and on three parts (anterior, middle, and posterior) of the tongue dorsum (tS) were measured using a commercial sulfide-monitoring device. RESULTS: : The pS levels of the three representative sites were reduced significantly following the initial therapy (p < 0.05). However, there was no significant reduction of the tS level in all three parts of the tongue. CONCLUSIONS: : The initial periodontal therapy such as oral hygiene and SRP reduces the sulcular sulfide level but not the tongue sulfide level. This suggests that sulcular sulfide level may be a possible indicator for assessing the outcome of initial periodontal treatment.

Adult↗
PubMed2003

Relationship between periodontal pocket sulfide levels and subgingival species.

BACKGROUND: Many species implicated in the pathogenesis of periodontal disease produce volatile sulfur compounds (VSC). This investigation examined the relationship between levels of sulfide and subgingival bacterial species in the same periodontal pockets. MATERIAL AND METHODS: Twenty chronic periodontitis subjects were measured clinically at six sites per tooth for plaque, gingivitis, bleeding on probing, suppuration, pocket depth and attachment level. Subgingival plaque samples, taken from the mesial aspect of each tooth, were individually analyzed for their content of 40 bacterial species using checkerboard DNA-DNA hybridization. Sulfide levels were measured at the same sites using a Diamond Probe/Perio 2000 system. Clinical and microbiological data were averaged for sulfide-positive and -negative sites separately in each subject and then averaged across subjects. Significance differences in clinical and microbial parameters between sulfide-positive and -negative sites were sought using the Wilcoxon signed ranks test. RESULTS: Mean total DNA probe counts (x10(5), +/-SEM) at sulfide-negative and -positive sites were 44.0 +/- 9.9 and 65.0 +/- 13.3, respectively (p < 0.01). Seventeen species were found at significantly higher levels in sulfide-positive than -negative sites. These included abundant producers of VSC such as members of the genera Fusobacterium, Campylobacter, Prevotella, Treponema and Eubacterium, and Bacteriodes forsythus, Selenomonas noxia and Propionibacterium acnes. Prevotella intermedia, Bacteriodes forsythus, Prevotella nigrescens, Fusobacterium nucleatum ss vincentii and Treponema denticola exhibited the greatest difference in mean counts between sulfide-negative and -positive sites. Orange and red complex species were at higher counts at shallow (< 4 mm) sulfide-positive than shallow sulfide-negative sites. Although not statistically significant, mean clinical parameters were somewhat higher at sulfide-positive than sulfide-negative sites. CONCLUSIONS: Intra-pocket sulfide levels reflect the levels of sulfide-producing species and may provide useful diagnostic information.

Adult↗
PubMed2003

Breath malodor in an asthmatic patient caused by side-effects of medication: a case report and review of the literature.

OBJECTIVE: The purpose of this report is to document the presence of dimethyl sulfide in mouth air as the predominant volatile sulfur compound (VSC) in an asthmatic patient who was regularly taking suplatast tosilate. STUDY DESIGN: The patient was a 33-year-old woman who complained of bad breath. She had been diagnosed as having asthma and was receiving periodical medical examinations once a month. VSC in her mouth air were measured with a gas chromatograph. Oral physiotherapy was also carried out to remove any oral malodor of which the source was intraoral. RESULTS: With the improvement in oral hygiene and periodontal conditions, the level of VSC was reduced but dimethyl sulfide still remained as the predominant VSC. CONCLUSIONS: Dimethyl sulfide metabolized from suplatast tosilate may be a potential cause of halitosis.

Adult↗
PubMed1995

Catalytic determination of sulfide in blood.

A catalytic method, based on the iodine-azide reaction, of the determination of sulfide in whole human blood is described. The method involves generation of hydrogen sulfide in an evolution-absorption apparatus by addition of sulfuric acid and subsequent trapping of the generated hydrogen sulfide in sodium hydroxide solution. The catalytic method allows the determination of sulfide without any interference from other sulfur compounds present in blood. A linear calibration graph was obtained over the range 1 x 10(-6)-5 x 10(-4) mol dm-3 sulfide and the proposed method is compared with an ion-selective electrode method.

Azides↗
PubMed2001

Catalytic hydrogen evolution in cathodic stripping voltammetry on a mercury electrode in the presence of cobalt(II) ion and phenylthiourea or thiourea.

The system Co(II)-phenylthiourea (PTU)-borax buffer was investigated by cathodic stripping voltammetry (CSV) at a hanging mercury drop electrode. The results of the voltammetric measurements showed that the presence of both PTU and Co(II) gives rise to a new irreversible peak at about -1.5 V. Based upon our previous results obtained in the study of other sulfur compounds and the sulfide ion itself, the peak was ascribed to the catalytic hydrogen evolution superimposed on the reduction of the coordinated Co(II) ion. The catalyst itself is a Co(II) complex with the sulfide ion produced by the decomposition of the analyte during the deposition step. The influence of PTU and cobalt concentration, accumulation conditions and stripping parameters was investigated and complementary data on thiourea are included. The results showed that the measurement of the catalytic hydrogen evolution peak current can be used as a basis for a simple, accurate and rapid method for the determination of PTU within the concentration range 10-100 nM. The catalytic method is relatively free of interferences and could be a suitable alternative for cases in which the stripping peak due to mercury ion reduction in the accumulated mercury compound is disturbed by some interference.

Journal Article↗
PubMed2004

Exploring the boundaries of a light-driven molecular motor design: new sterically overcrowded alkenes with preferred direction of rotation.

Insight in the steric and electronic parameters governing isomerization processes in artificial molecular motors is essential in order to design more advanced motor systems. A subtle balance of steric parameters and the combination of helical and central chirality are key features of light-driven unidirectional rotary molecular motors constructed so far. In an approach to decrease the steric hindrance around the central olefinic bond (rotary axis) and thereby lowering the energy barrier for helix inversion resulting in an increased rotation rate, the boundaries of our molecular motor design are explored. In a new design of a light-driven molecular motor based on a sterically overcrowded alkene the methyl substituent adjacent to the stereogenic center, which is responsible for the control of the direction of rotation, is shifted one position away from the fjord region of the molecule compared to the second-generation motor systems. In contrast to previously developed light-driven molecular motors, there is a preference for the methyl substituent to adopt a pseudo-equatorial orientation. Nevertheless, this new type of motor is capable of functioning as a rotary molecular motor, albeit not with full unidirectionality. Under the combined influence of light and heat, there is a preferred clockwise rotation of one half of the molecule. Surprisingly, the effect of shifting the methyl substituent on the energy barrier for helix inversion is small and even a slight increase in the barrier is observed.

Alkenes↗