Pyridine-2-thione, and

Some general observations for 4-nitroimidazo[4,5- ]pyridin-2-ones, imidazo[4,5- ]pyridine-2-thiones, imidazo[4,5-f]pyridine-2-thiones, imidazo[4,5- ]quinolin-2-ones, isothiazolo[5,4- ]pyridine-2-thiones, and 3/f-l,2-dithiolo[4,3-f]pyridine-3-thiones are reported in <1996CHEC-II(7)283>. The majority of compounds in this review have been isolated using standard chromatographic techniques. 

A study on the preparation of a relatively large number of imidazo[4,5-fr]pyridine-2-thiones and imidazo[4,5-c]pyridine-2-thiones demonstrates that the solubility of these compounds is poor in most solvents <88CHE653>. 

Examples of ring closures with c-amino mercapto heterocyclic compounds are the reactions of carbon disulfide with o-amino mercapto pyridines and o-amino mercapto quinolines, which respectively yield dihydrothiazolo pyridine-2-thiones and dihydrothiazolo qumohne-2-thiones. A summary of these compounds are 7 ... 

Pyrimidine Derivatives. Lam and coworkers have also published the preparation of 3,4,6-trisubstituted-2-pyridones 49, pyridine-2-thiones, and pyrimidine-2-ones 50 and... 

Thiazolo[3,2-a]pyridines (CaNS-CjN).— The established synthesis of thia-zolo[3,2-a]pyridines from pyridine-2-thiones and a-bromo-a -unsaturated carbonyl compounds (these Reports, Vol. 1, p. 432 Vol. 2, p. 698) has been further studied. The use of the isomeric a-bromocrotonic acids yields the expected bicyclic products (202), exclusively of the 2,3-trans-configuration, owing to the concurrent isomerization of the cis- to the trans-acid. Activated acetylenes undergo a comparable Michael-addition-cyclization process. Thus, acetylenedicarboxylic acid affords trans-2,3-dicarboxydi-hydrothiazolo[3,2-a]pyridinium salts (204). The intermediate vinyl... 

To release the pyridine-2-thione leaving group and form the free sulfhydryl, add DTT at a concentration of 0.5 mg DTT per mg of modified protein. A stock solution of DTT may be prepared to make it easier to add it to a small amount of protein solution. In this case, dissolve 20mg of DTT per ml of 0.1M sodium acetate, 0.1M NaCl, pH 4.5. Add 25 pi of this solution per mg of modified protein. Release of pyridine-2-thione can be followed by its characteristic absorbance at 343 nm (s = 8.08 X 103M 1cm 1). 

Reduction of the pyridyl disulfide end after SPDP modification releases the pyridine-2-thione leaving group and generates a terminal—SH group. This procedure allows sulfhydryl-reactive derivatives such as maleimide-activated enzymes (Chapter 26, Section 2.3) to be conjugated with DNA probes for use in hybridization assays (Malcolm and Nicolas, 1984). 

N-(10-Undecenoyloxy)pyridine-2-thione (3). To an oven-dried, one-necked, 250-mL, round-bottomed flask equipped with a nitrogen inlet with gas bubbler, a magnetic stirrer, and a dropping funnel are added 3.61 g (28.4 mmol) of N-hydroxythiopyridone (2) (Note 1), 6.20 g (30.0 mmol) of dicyclohexylcarbodiimide... 

Attaching cyclic, bidentate 1-hydroxy-177-pyridin-2-thione, 1-hydroxy-177-pyridin-2-one (1,2-HOPO) and 2-hydroxy-277-isoquinolin-l-one (1,2-HOIQO) ligating units via their C-6 carbon to TREN template produced 19 , 20 and 21 , respectively. 

The PE spectra of hydroxy- and mercapto-pyridines have been examined, together with the model iV-alkyl and S- or O-alkyl compounds, to elucidate the tautomeric equilibria in the vapor phase (77JCS(P2)1652) (Section 2.04.4.2). Figure 21 and Table 13 show details of the PE spectra of l-methylpyridin-2-one, 2-methoxypyridine and the tautomeric mixture at equilibrium of pyridin-2-one and 2-hydroxypyridine. This indicates that there is approximately 25% of oxo form present once adjustment has been made for the expected influence of methylation, similar measurements reveal ca. 10% of the thione form in the mercapto-thione equilibrium. Other spectra indicate that 3- and 4-hydroxy- and 3- and 4-mercapto-pyridine exist in the vapor phase with less than 5% of the alternative tautomer present. 

In line with Beak s finding, pyridin-2-one was estimated to be 31 kJ mol-1 less aromatic than the pyridine, and a similar figure of 25 was estimated for pyridine-2-thione. Subsequent results (73JCS(P2)1080, 76AHC(S1)71) on the pyridin-4-one, quinolin-2-one and isoquinolin-1-one series showed that aromatic resonance energy difference for the pyridin-4-one/4-hydroxypyridine system was very similar to that for the 2-substituted compounds, in contrast to Beak s findings. 

Pyridine-2-thione-A-oxycarbonyl (PTOC) derivatives of carboxylic esters 53 were developed by Barton et al. and serve as a convenient source of acyloxyl radicals, which upon decarboxylation provide specific routes to free radicals (equation 82). This process can also proceed by a radical addition (equation 83). Acyl selenides (54) are a convenient source of acyl radicals, which can undergo decarbonylation also giving specific free radicals (equation 84). ° ... 

Numereous derivatives of benzimidazole, naphthoimidazoles and other condensed imidazole systems can be very effectively thiated with elemental sulfur on heating without solvent at 230-260°C. The product of this reaction is the corresponding imidazolin-2-thione formed in excellent yield (67ZOR1518, 95IZV2231). For example, imidazo[4,5-cjpyridines (329, R =H, Aik, Ar, C6H5CH2) gave 1,3-dihydro-2//-imidazo[4,5-c]pyridine-2-thiones (330). 

Chloro-l-methylpyridinium iodide (683) functions as an important mediator in a variety of different reactions. Esters are formed in high yield from acids and alcohols when reacted with one equivalent of (683) in the presence of two equivalents of triethylamine (Scheme 158) (75CL1045). cv-Hydroxy acids are lactonized under similar conditions (76CL49). The pyridinium salt (683) will also convert thioureas into carbodiimides (77CL575) and pyridine-2-thiones to pyridyl sulfides (75CL1159). 

A soln of 1.5 mM DTDP in 0.5 M Nad/0.05M pH 7.5 phosphate buffer, containing 6M Gdn-HCl (to enhance exposure and reactivity of SH groups) and 1 mM EDTA (to bind metal ions and thereby prevent air oxidation of SH groups during the assay) was prepared. A sample of the protein soln (100 pi) was added to 0.05 M pH 7.5 phosphate buffer (0.8 mL) with the DTDP soln prepared above (0.1 mL). The reagent blank consisted of 0.05 M pH 7.5 phosphate buffer (0.8 mL), the DTDP soln prepared above (0.1 mL), and the buffer used to dissolve the protein (0.1 mL). From the amount of pyridine-2-thione (molar absorptivity 8.08 x 103 at 343 nm) released, the SH groups can be quantitated.1951... 

Undheim and Riege267 obtained 1 1 adducts from pyridine-2-thiones (60) and acetylenic amides, esters, and ketones. The reaction rate increases with increase in activation of the acetylenic bond by the adjacent carbonyl group and is affected by the pyridine 6-substituent, which may also affect the stereochemical course. Product-isomer ratios corresponding to kinetic control were obtained in chloroform. Amides gave E isomers, ketones gave Z, and esters a slight preponderance of the E isomers (61). Successive addition of n-butyllithium and DMAD to... 

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