Pyridine-3-thiol, 4-amino

The tautomerism between 2-pyridinethione and 2-pyridine thiol has also been examined using variable temperature IR spectroscopy <2002JOC9061>. No evidence for the S-H stretch was observed in a range of solvents and this was determined computationally to be a solvent effect the thiol form is more stable in the gas phase but the thione is more stable in solution. (The effect of phase on the tautomers of 2-hydroxy, 2-amino-, and 2-thiopyridine has also been studied by infrared spectroscopy <2001SAA2659>.) Dimerization is also observed, with the indication that the thione dimer predominates, in contrast with the computational studies described above. 

Table 3 gives the corresponding physical properties of some commercially important substituted pyridines having halogen, carboxyHc acid, ester, carboxamide, nitrile, carbiaol, aminomethyl, amino, thiol, and hydroxyl substituents. 

Methyl- l-[methyl-(2-pyridin-2-yl-ethyl)amino]propane-2-thiol (108) is a tridentate N2S ligand with an aliphatic thiolate ligand. The single-crystal X-ray structures demonstrate that the zinc complexes are close structural analogs of the His2Cys site found in peptide deformylase.873... 

With pyridine/S03 complex at higher temperatures (70-80 °C), in addition to sulfation of phenolic, hydroxy, and thiol groups, sulfation of amino, guanidino, and primary amido... 

The p-sulfanyl amides 28 are synthesized from N-protected amino acids 24 via amino alcohols 25, which are converted into (5-acetylsulfanyl amides 26 by a Mitsunobu reaction. The (5-amine disulfide 27 is subsequently coupled with a variety of carboxylic acids, followed by reduction with tributylphosphine in aqueous THF in the presence of pyridine to produce the free thiol 28 (Scheme 5).1211 Detailed experimental procedures for these compounds have not been reported. 

A modification of the Pinner reaction using liquid HF has been used to improve the yields of the dithioester products. The N-protected amino acid and peptide nitriles 6 dissolve in liquid HF at temperatures below 0°C and react with thiols to form the imidothioic acid ester hydrofluorides 7 that further react with H2S in pyridine at 0°C to form the dithioesters 8 (Scheme 2)J71 Several isotopic dithioesters have been synthesized by this method with improved yield (Table 2). The use of liquid HF at low temperature helps to dissolve the amino acid nitriles that are not very soluble under Pinner conditions (HCl-saturated CH2C12). 

These reagents in the presence of a solvent (such as pyridine, acetonitrile, dimethylformamide) rapidly effect trimethylsilylation, often at room temperature, of hydroxyl, amino, imino, amido, thiol and carboxyl groups whether in mono- or polyfunctional compounds. Frequently a sample of the reaction mixture may be loaded directly on to the g.l.c. column, although in some cases removal of the small amount of solvent which is present may improve subsequent analysis of the chromatographic trace. Proprietary reagent formulations are available from Pierce Chemical Co., pioneers in this field and publishers of detailed procedures suited to particular groups of compounds. 

Useful for such compounds as sugars, phenols, alcohols, amines, thiols, steroids especially recommended for citric acid cycle compounds and amino acids reaction is often carried out in pyridine or dimethyl formamide (the latter being preferred for 17-keto steroids) care must be taken to eliminate moisture lowest silyl donating strength of all common silating reagents... 

In order to obtain a heterodimeric disulfide bridge the cysteine residue of one component, either PNA or peptide, must be derivatized. 3-Nitro-2-pyridine-sulphenyl (NPys)-derivatized Cys is specifically reactive toward free thiols. Npys-labeled Cys is commercially available and with special cautions (see Note 3) can be assembled into a peptide chain like a commonly protected amino acid. 

The rearrangement also occurs when 2-hydrazino-5-nitropyridine is treated with cyanogen bromide and carbon disulfide to result in 2-amino-6-nitro-[l,2,4]triazolo[l,5-fljpyridine and 6-nitro-[l,2,4]triazolo[l,5-fl]pyridine-2-thiol, respectively (70JHC1019). The rearrangement has also been used (76JOC3124) for the synthesis of nucleosides of the [1,5-a] system. 

Historically, the first practicable reagent for the synthesis of N -Boc amino acids, tert-butyl 4-nitrophenyl carbonate (52), was developed by Anderson and McGregorb (Scheme 25). Due to the low reactivity of this mixed carbonate, drastic reaction conditions are required and yields remain unsatisfactory because of the difficult and laborious separation of the byproduct 4-nitrophenol. Alternative mixed carbonates have been proposed such as tert-butyl 2,4,5-trichlorophenyl carbonate (53),b32] lert-butyl pentachlorophenyl carbonate (54),b33] tert-butyl 2-pyridyl carbonate (55)0-tert-hvXy 5-4,6-dimethylpyrimidin-2-yl thiocarbonate (56).b3 1 With the latter two reagents the byproducts, pyridin-2-ol and 4,6-dimethylpyrimidine-2-thiol, respectively, are acid soluble and, thus, readily removed. 

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