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The biosynthesis of the thiazole phosphate moiety of thiamin: the sulfur transfer mediated by the sulfur carrier protein ThiS.

Thiamin-pyrophosphate is an essential cofactor in all living systems. The biosynthesis of both the thiazole and the pyrimidine moieties of this cofactor involves new biosynthetic chemistry. Thiazole-phosphate synthase (ThiG) catalyses the formation of the thiazole moiety of thiamin-pyrophosphate from 1-deoxy-D-xylulose-5-phosphate (DXP), dehydroglycine and the sulfur carrier protein (ThiS), modified on its carboxy terminus as a thiocarboxylate (ThiS-thiocarboxylate). Thiazole biosynthesis is initiated by the formation of a ThiG/DXP imine, which then tautomerizes to an amino-ketone. In this paper we study the sulfur transfer from ThiS-thiocarboxylate to this amino-ketone and trap a new thioenolate intermediate. Surprisingly, thiazole formation results in the replacement of the ThiS-thiocarboxylate sulfur with an oxygen from DXP and not from the buffer, as shown by electrospray ionization Fourier transform mass spectrometry (ESI-FTMS) using (18)O labeling of the 13C-, 15N-depleted protein. These observations further clarify the mechanism of the complex thiazole biosynthesis in bacteria.

Amino Acid Sequence↗

Synthesis and binding properties of oligo-2'-deoxyribonucleotides covalently linked to a thiazole orange derivative.

Thiazole orange label was coupled to the eighth phosphate of a pentadeca-2'-deoxyriboadenylate via a phosphoramidate linkage using different linkers. The stereoisomers were separated, and their absolute configurations were determined. Finally, the thiazole orange moiety was also linked to the tenth phosphate of icosathymidylates in both the alpha and the beta series via a phosphoramidate linkage. Once again, the thiazole orange-icosathymidylate conjugates were obtained as pure stereoisomers. The binding properties of these oligo-2'-deoxyribonucleotide-thiazole orange conjugates with their complementary sequences were studied by absorption spectroscopy. The covalent attachment of the thiazole orange derivatives to the oligoadenylates stabilizes the complexes formed with both the DNA and RNA targets. On the contrary, when the thiazole orange is tethered to the oligo-alpha-thymidylate or oligo-beta-thymidylate, no significant stabilization of the duplexes formed with poly r(A) can be observed.

Amides↗

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↗

Synthesis of some new 5-(2-substituted-1,3-thiazol-5-yl)-2-hydroxy benzamides and their 2-alkoxy derivatives as possible antifungal agents.

The 2-hydroxy-5-(1,3-thiazol-5-yl) benzamide (4a), 5-(2-amino-1, 3-thiazol-5-yl)-2-hydroxy benzamide (4b), 2-hydroxy-5-(2-alkyl-1,3-Thiazol-5-yl) benzamide (4c and 4d), 5-(2-[(N-substituted aryl)amino]-1,3-thiazol-5-yl)2-hydroxy benzamides (6a-j) were prepared by reacting 5-(bromoacetyl) salicylamide (2) with thiourea, thioformamide, thioalkylamide (3c-d) and substituted thioureas (5a-j) in absolute ethanol. These compounds were converted to 5-(2-substituted-1,3-thiazol-5-yl)-2-alkoxybenzamides and 5-(2-N-(substituted aryl)-1,3-thiazol-5-yl)-2-alkoxy benzamides (8a-g) by reacting with n-alkylbromides (7a-b) in presence of a base. The newly synthesized compounds were characterized by IR, (1)H-NMR and mass spectral data. Compounds were also screened for their antifungal activity.

Antifungal Agents↗

Thiamin biosynthesis in Bacillus subtilis: structure of the thiazole synthase/sulfur carrier protein complex.

Thiazole synthase is the key enzyme involved in the formation of the thiazole moiety of thiamin pyrophosphate. We have determined the structure of this enzyme in complex with ThiS, the sulfur carrier protein, at 3.15 A resolution. Thiazole synthase is a tetramer with 222 symmetry. The monomer is a (betaalpha)(8) barrel with similarities to the aldolase class 1 and flavin mononucleotide dependent oxidoreductase and phosphate binding superfamilies. The sulfur carrier protein (ThiS) is a compact protein with a fold similar to that of ubiquitin. The structure allowed us to model the substrate, deoxy-D-xylulose 5-phosphate (DXP), in the active site. This model identified Glu98 and Asp182 as new active site residues likely to be involved in the catalysis of thiazole formation. The function of these residues was probed by mutagenesis experiments, which confirmed that both residues are essential for thiazole formation and identified Asp182 as the base involved in the deprotonation at C3 of the thiazole synthase DXP imine. Comparison of the ThiS binding surface to the surface of ubiquitin identified a conserved hydrophobic patch of unknown function on ubiquitin that may be involved in complex formation between ubiquitin and one of its binding partners.

Bacillus subtilis↗

Mass spectrometry of 2-substituted 5-nitro-2-furyl thiazoles. Identification of microsomal nitroreduction products by electron impact mass spectrometry.

The electron impact mass spectral fragmentation of nitro heterocyclic carcinogens N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide, 2-amino-4-(5-nitro-2-furyl)thiazole, 2-methyl-4-(5-nitro-2-furyl)thiazole and 2-methylamino-4-(5-nitro-2-furyl)thiazole were studied. The molecular ions undergo two modes of cleavage: one giving [M-84]+ ions which include the 2-substituted thiazole ring, while the other gives rise to the fragment [M-74]+ ions. The products of anaerobic microsomal nitroreduction of 2-methyl-4-(5-nitro-2-furyl)thiazole were isolated and purified by high-pressure liquid chromatography. The metabolites undergo different fragmentation patterns compared to the parent nitro analogs. Metabolites from anaerobic enzymatic reduction showed identical gas chromatographic, high-pressure liquid chromatographic and thin-layer chromatographic properties to the chemically synthesized material. The metabolites were identified as 1-(2-methyl-4-thiazolyl)-3-cyano-1-propenone and 1-(2-methyl-4-thiazolyl)-3-cyano-1-propane by mass spectral fragmentation pattern.

Animals↗

Fluorometric determination of thiazole-containing compounds.

Fluorescence spectroscopy was applied to the development of sensitive analytical methods for the determination of thiazole and several congeners that contain substituted thiazole rings. Treatment to yield thionine, previously used spectrophotometrically to measure thiazole and fluorometrically only for sulfur determinations in inorganic systems, is further characterized and illustrated with the determination of the antibiotic thiopeptin. This method is selective for submicrogram quantities of thiazole rings in the presence of fused-ring derivatives and reduced analogs. It has a precision of +/- 2% RSD (n = 11) at the 15-ng/ml thiazole concentration level with a signal-to-noise ratio of 3:1. For thiopeptin, this method has an accuracy of 5% mean relative error (n = 8) over the 5--20-ppm range in medicated feed.

Animal Feed↗

Application of thiazole dyes to amyloid under conditions of direct cotton dyeing: correlation of histochemical and chemical data.

The fluorescent brightening agent Phorwhite (Blankophor) BBU imparts intense selective fluorescence to amyloid, but this modern reagent is no longer readily available on the biological dye market. Conventional Thioflavine S and T stains require differentiation and are not specific. To improve selectivity, direct and cationic thiazole dyes were substituted in the alkaline Congo Red and the Phorwhite BBU procedure. With the former technic Diphenyl Brilliant Yellow 8G, Clayton Yellow, Thiazol Yellow, Thioflavine T and Seto Flavine T imparted strong to intense selective fluorescence to amyloid. Under the conditions of the Phorwhite BBU reaction these dyes were suitable only for formalin-fixed amyloid. Several thiazole dyes did not fluoresce. Fluorescence is a function of the molecular orbital system, the thiazole rings per se cannot induce fluorescence. Paper chromatograms indicated two or more fractions in the dyes studied. Different samples of the same dye can vary significantly in their staining and fluorescence properties. This heterogeneity is inherent in the mode of synthesis. In some cases the cationic thiazole dyes rendered certain amyloid deposits, e.g. in vessel walls, intensely fluorescent; other amyloid deposits in the same sections showed only weak fluorescence. Further studies are required to correlate these peculiar patterns with immunological data on amyloid types.

Amyloid↗

Bisintercalation of homodimeric thiazole orange dyes in DNA: effect of modifying the linker.

The thiazole orange dye 1,1'-(4,4,8,8-tetramethyl-4,8-diazaundecamethylene)-bis[4-[3-methy l-2, 3-dihydro(benzo-1,3-thiazole)-2-methylidene]]quinolinium tetraiodide (TOTO) binds to double-stranded DNA (dsDNA) in a sequence selective bisintercalation. Each chromophore is sandwiched between two base pairs in a (5'-CpT-3'):(5'-ApG-3') site, and the linker spans over two base pairs in the minor groove. The binding of analogs of TOTO in which the linker has been modified is examined. The aim of the study is to utilize the sequence selectivity of the TOTO chromophores to enhance and/or alter the overall selectivity of the binding. One- and two-dimensional 1H-NMR investigations of complexes between TOTO analogs and various dsDNA oligonucleotides are reported. The following analogs were synthesized and used: 1,1'-(4,4,8,8-tetramethyl-4,8-diazadodecamethylene) -bis[4-[3-methyl-2,3-dihydro- (benzo-1,3-thiazole)-2-methylidene]]quinolinium tetraiodide (TOTO10), 1,1'-(5,5,9,9-tetramethyl-5,9-diazatridecamethylene)-bis[4-[3-meth yl-2, 3-dihydro(benzo-1,3-thiazole)-2-methylidene]]quinolinium tetraiodide (TOTO11), and 1,1'-(6,6,10,10-tetramethyl-6,10-diazapentadecamethylene)-bis[4-[3 -methyl-2, 3-dihydro(benzo-1,3-thiazole)-2-methylidene]]quinolinium tetraiodide (TOTO13). The results show that with a longer linker the dyes can bisintercalate into two (5'-CpT-3'):(5'-ApG-3') sites separated by one or two base pairs. Bisintercalation in two such "isolated" binding sites yields non-nearest-neighbor bisintercalation in which the linker spans over more than two base pairs. The investigations also showed that an exact length of the linker is not crucial for the site selectivity since TOTO, TOTO10, and TOTO11 are almost equally suitable in binding selectively to the (5'CTAG-3')2 sequence. Fluorescence measurements show that TOTO10, TOTO11, and TOTO13 have higher fluorescence quantum yields than TOTO when bound to d(CGCTAGCG)2. This indicates that the length of the linker in TOTO may not be the optimum one in terms of using the dye as a fluorescence marker.

Benzothiazoles↗

Amino- and urea-substituted thiazoles inhibit photosynthetic electron transfer.

Amino- and urea-substituted thiazoles exhibited in vivo herbicidal activity on duckweed (Lemna paucicostata Hegelm. strain 6746) cultures and appeared to act via inhibition of photosynthetic electron transport system. A small number of the thiazole derivatives tested were active but only at relatively high concentrations. The most active structures were the amino-substituted thiazoles with isopropyl and n-butyl side chains and the urea-substituted thiazole with p-chlorophenyl side chain. Decreasing the length of the side chain had a negative effect on the PSII inhibitory activity. The urea-substituted series was as a group less active than the amino series, and the free acid series had no biological activity. The most active compounds competed for the same binding site as atrazine on PSII. Computer modeling highlighted the structural similarities between some of the thiazoles and the commercial herbicides diuron and atrazine.

Amines↗

Thienylimidazo[2,1-b]thiazoles as inhibitors of mitochondrial NADH dehydrogenase.

The synthesis of 6-substituted 5-(thienylvinyl)imidazo[2,1-b]thiazoles and 6-thienylimidazo[2,1-b]thiazoles is reported. These compounds were tested as specific inhibitors of the NADH: ubiquinone (UBQ) reductase activity of NADH dehydrogenase in mitochondrial membranes. The 6-thienylimidazo[2,1-b]thiazoles were more potent in mammalian than in nematode mitochondria and had an average titer of 0.11 mM for 2-methyl-6-(2-thienyl)imidazo[2,1-b]thiazole (10). This compound is noncompetitive with the ubiquinone substrate and interacts with a site which is mutually exclusive with that of rotenone but nonexclusive with that of piericidin and several other inhibitors of NADH dehydrogenase. In the series of 5-(thienylvinyl)imidazothiazoles, the hydrobromide of (E)-6-chloro-5-(2-thienylvinyl)imidazo[2,1-b]thiazole (E-5.HBr) was found to be more potent as an inhibitor of the NADH:UBQ activity (IC50 = 15-17 microM) than the 6-thienylimidazoles such as 10. The inhibitory action of E-5.HBr and its analogs is different from that of compound 10 as indicated by the mutual exclusivity with other inhibitors and the relative inhibition of the activity with various electron acceptors.

Animals↗

(Methoxyalkyl)thiazoles: a new series of potent, selective, and orally active 5-lipoxygenase inhibitors displaying high enantioselectivity.

(Methoxyalkyl)thiazoles are novel 5-lipoxygenase (5-LPO) inhibitors that are neither redox agents nor iron chelators. Consideration of a hypothetical model of the enzyme active site led to this series which is exemplified by 1-[3-(naphth-2-ylmethoxy)phenyl]-1-(thiazol-2-yl)propy l methyl ether (2d, ICI211965). 2d inhibits cell-free guinea pig 5-LPO activity, LTC4 synthesis in plasma free mouse macrophages, and LTB4 synthesis in rat and human blood (IC50s 0.1 microM, 8 nM, 0.5 microM, and 0.4 microM, respectively) but does not inhibit the synthesis of cyclooxygenase products at concentrations up to 50 microM in macrophages and 100 microM in blood. 2d is orally active in rat (ex vivo ED50 10 mg/kg in blood taken in 1 h after dosing). SAR studies show that high in vitro potency requires methoxy, thiazolyl, and naphthyl groups and depends critically on the substitution pattern. (Methoxyalkyl)thiazoles are chiral. Resolution of 1-methoxy-6-(naphth-2-ylmethoxy)-1-(thiazol-2-yl)indan (2j, ICI216800) shows that (+)-2j is 50-150-fold more potent than (-)-2j in in vitro assays. Thus, (methoxyalkyl)thiazoles are a new series of orally active, selective 5-LPO inhibitors and represent the first class of inhibitors in which inhibition is mediated by specific, enantioselective interactions with the enzyme.

Administration, Oral↗

Structure of the thiazole biosynthetic enzyme THI1 from Arabidopsis thaliana.

Thiamin pyrophosphate is an essential coenzyme in all organisms that depend on fermentation, respiration or photosynthesis to produce ATP. It is synthesized through two independent biosynthetic routes: one for the synthesis of 2-methyl-4-amino-5-hydroxymethylpyrimidine pyrophosphate (pyrimidine moiety) and another for the synthesis of 4-methyl-5-(beta-hydroxyethyl) thiazole phosphate (thiazole moiety). Herein, we will describe the three-dimensional structure of THI1 protein from Arabidopsis thaliana determined by single wavelength anomalous diffraction to 1.6A resolution. The protein was produced using heterologous expression in bacteria, unexpectedly bound to 2-carboxylate-4-methyl-5-beta-(ethyl adenosine 5-diphosphate) thiazole, a potential intermediate of the thiazole biosynthesis in Eukaryotes. THI1 has a topology similar to dinucleotide binding domains and although details concerning its function are unknown, this work provides new clues about the thiazole biosynthesis in Eukaryotes.

Adenosine Triphosphate↗

In vitro microsomal metabolic studies on a selective mGluR5 antagonist MTEP: characterization of in vitro metabolites and identification of a novel thiazole ring opening aldehyde metabolite.

In vitro liver microsomal studies revealed that [14C] MTEP (3-[2-methyl-1,3-thiazol-4-yl)ethynyl] pyridine) was metabolized into three major oxidative metabolites. Metabolite 1 (M1) was shown to be a hydroxymethyl metabolite; M2 was shown to be a pyridine oxide. Moreover, a novel aldehyde metabolite (M3) was identified from mouse liver microsomes. The structure of the aldehyde M3 was elucidated by LC/MS/MS. In addition, methoxyamine, an aldehyde-trapping agent, and accurate mass measurement using a high-resolution quadrupole-time of flight (Q-TOF) instrument, were used to confirm the proposed thiazole ring-opening structure of M3. A mechanism for aldehyde M3 formation was postulated based on MTEP incubation studies with 18O2 and H2 18O using mouse liver microsomes. MTEP was initially oxidized at sulfur, followed by subsequent C4-C5 of thiazole epoxidation, thiozole ring opening and further oxidative desulfation. This proposed thiazole ring-opening mechanism might represent a novel metabolism pathway for xenobiotics containing a thiazole moiety. Species differences in the metabolism of MTEP were observed in mouse, rat, dog, monkey and human liver microsomes. Mouse appears to generate all three oxidative metabolites to a greater extent than other species examined.

Aldehydes↗

The pharmacokinetics of a thiazole benzenesulfonamide beta 3-adrenergic receptor agonist and its analogs in rats, dogs, and monkeys: improving oral bioavailability.

The pharmacokinetics and oral bioavailability of (R)-N-[4-[2-[[2-hydroxy-2-(pyridin-3-yl)ethyl]amino]ethyl]phenyl]-4-[4-[4-(trifluoromethylphenyl]thiazol-2-yl]benzenesulfonamide (1), a 3-pyridyl thiazole benzenesulfonamide beta3-adrenergic receptor agonist, were investigated in rats, dogs, and monkeys. Systemic clearance was higher in rats (approximately 30 ml/min/kg) than in dogs and monkeys (both approximately 10 ml/min/kg), and oral bioavailability was 17, 27, and 4%, respectively. Since systemic clearance was 25 to 40% of hepatic blood flow in these species, hepatic extraction was expected to be low, and it was likely that oral bioavailability was limited either by absorption or a large first-pass effect in the gut. The absorption and excretion of 3H-labeled 1 were investigated in rats, and only 28% of the administered radioactivity was orally absorbed. Subsequently, the hepatic extraction of 1 was evaluated in rats (30%) and monkeys (47%). The low oral bioavailability in rats could be explained completely by poor oral absorption and hepatic first-pass metabolism; in monkeys, oral absorption was either less than in rats or first-pass extraction in the gut was greater. In an attempt to increase oral exposure, the pharmacokinetics and oral bioavailability of two potential prodrugs of 1, an N-ethyl [(R)-N-[4-[2-[ethyl[2-hydroxy-2-(3-pyridinyl)ethyl]amino]ethyl]phenyl]-4-[4-[4-(trifluoromethyl)phenyl]thiazol-2-yl]benzenesulfonamide; 2] and a morpholine derivative [(R)-N-[4-[2-[2-(3-pyridinyl)morpholin-4-yl]ethyl]phenyl]-4-[4-[4-(trifluoromethyl)- phenyl]thiazol-2-yl]benzenesulfonamide; 3], were evaluated in monkeys. Conversion to 1 was low (<3%) with both derivatives, and neither entity was an effective prodrug, but the oral bioavailability of 3 (56%) compared with 1 (4%) was significantly improved. The hypothesis that the increased oral bioavailability of 3 was due to a reduction in hydrogen bonding sites in the molecule led to the design of (R)-N-[4-[2-[[2-hydroxy-2-(pyridin-2-yl)ethyl]amino]ethyl]phenyl]-4-[4-(4-trifluoromethylphenyl)thiazol-2-yl]benzenesulfonamide (4), a 2-pyridyl beta3-adrenergic receptor agonist with improved oral bioavailability in rats and monkeys.

Administration, Oral↗

Biliary metabolites of the anti-inflammatory drug 2-acetamido-4-(chloromethyl)thiazole.

The mechanism for the formation of a class of sulfur-containing conjugates of xenobiotics was further investigated in this report. The major biliary metabolites of 2-acetamido-4-(chloromethyl)thiazole in the rat were found to be the mercapturic acid conjugate of 2-acetamido-4-methylthiazole and the glucuronic acid conjugate of 2-acetamido-4-(mercaptomethyl)thiazole. When these two compounds were introduced directly into the cecum of the rat, 2-acetamido-4-[(methylsulfinyl)methyl]thiazole and 2-acetamido-4-[(methylsulfonyl)methyl]thiazole were found as urinary metabolites. These results give strong support to a proposed mechanism in which intestinal microfloral metabolism of biliary metabolites, together with enterohepatic circulation, is necessary for the formation and urinary excretion of the 4-(methylthiomethyl), 4-(methylsulfinyl-methyl), and 4-(methylsulfonylmethyl) analogs of 2-acetamido-4-(chloromethyl)thiazole in the rat.

Animals↗

Demonstration that thiazole-orange-positive platelets in the dog are less than 24 hours old.

Approximately 6% of dog platelets are positive for staining with thiazole orange, a dye frequently used to stain ribonucleic acid. In this report, thiazole-orange positivity is shown to mark platelets that are less than 24 hours old. Dog platelets were derivatized in vivo with N-hydroxysuccinimido biotin such that greater than 95% of all platelets were biotinylated. Newly synthesized, nonbiotinylated platelets were then monitored by flow cytometry for their ability to bind thiazole orange. After biotinylation, the percentage of biotin-negative, thiazole-orange-positive platelets increased gradually from 0.72% at 30 minutes to 5.44% at 24 hours. These data indicate that thiazole-orange staining does label newly synthesized platelets.

Animals↗

On the utility of the azido transfer protocol: synthesis of 2- and 5-azido N-methylimidazoles, 1,3-thiazoles and N-methylpyrazole and their conversion to triazole-azole bisheteroaryls.

The azido transfer procedure of heteroaryllithium and tosyl azide was used to synthesize selected 2- and 5-azidoazoles. This procedure, which is based on the fragmentation of the appropriate lithium triazene salts 1a-7a, successfully afforded 2-azido-N-methylimidazole 1, 2-azido-1,3-thiazole 2, 2-azidobenzo-1,3-thiazole 3, 5-azido-N-methylpyrazole 4, 5-azido-N-methylimidazole 6[via 2-(trimethylsilyl)-5-azido-N-methylimidazole 5], and 5-azido-1,3-thiazole 7 (via 5-lithio-1,3-thiazole), but attempts to prepare 5-azido-2-(trimethylsilyl)-1,3-thiazole 8 from the corresponding triazene 7a failed, affording only the desilylated azide in poor yield. Azides - underwent 1,3-dipolar cycloaddition when mixed with neat (trimethylsilyl)acetylene, giving 1-heteroaryl-4-trimethylsilyl-1,2,3-triazoles 1b-7b generally in very high yields.

Journal Article↗