4- -2-amino-3-pyridinol

Similar methods lead to ring closure on a variety of other ring systems. The substituted pyrimidinethione 260 with polypho-sphoric acid formed the thiazolo [5,4-<7 pyrimidine 261 (Scheme 146) <1965JOG1916>. The cyclization of jV-acylated amino-pyridinols such as 262 affords oxazolopyridines 263 (Scheme 147) <2005TL9001, CHEC-III(4.04.9.3)524>. 

Alkyl-oxazolopyridines can also be synthesized from amino-pyridinols. The synthetic sequence starts with A -acylation of o-amino-pyridinols such as 214 (Scheme 64) <2005TL9001>. The resulting amide 215 was then cyclodehydrated with C2CI6 and PPhs to give oxazolopyridines 216. 

Hyperglycemia-induced oxidative stress has an important role in the pathogenesis of diabetic complications. Human monocytes exposed to 2-deoxy-D-ribose exhibited loss of cell viability, overproduction of ROS, depletion of glutathione, and apoptosis. Treatment with PLP inhibited these as well as lipid peroxidation and protein oxidation (4). Pyridoxine has a very high level of quenching of hydroxyl radicals (5). Mono- and bicyclic amino pyridinols have been synthesized from pyridoxine hydrochloride and have been shown to have antioxidant properties (6). 

Me2NCHO, warm then substrate slowly, reflux, 3 h 83%) the same substrate (219) with 2-amino-3-pyridinol (220, X = N) gave 12//-pyrido-[2, 3 5,6]oxazino[2,3-/7]quinoxaline (221, X = N) (likewise 72%) " and analogs were made somewhat similarly. ... 

Color Photography (see Section 5.7). Chromium 1 1 complexes such as 40 [79230-32-3] [65], and 1 2 chromium complexes, both containing a hydroquinone residue as developer group, are used as photo dyes [66], Nickel complexes of 2-amino-6-arylazo-3-pyridinol dyes can also be used for photographic purposes [67],... 

Wijtmans, M. Pratt, D. A. Valgimigli, L. DiLabio, G. A. Pedulli, G. F. Porter, N. A. 6-Amino-3-pyridinols towards diffusion-controlled chain-breaking antioxidants. Angew. Chem. Int. Ed. 2003, 42, 4370-4373. 

Acid hydrolysis of 5-amino-5-deoxy-l,2-0-isopropylidene-o -D-xy-lofuranose (15) might be expected to afiFord 5-amino-5-deoxy-D-xylose, but instead, at 70 , 3-pyridinol (21) is the main product. If the acid hydrolysis of compound 15 is conducted at room temperature, there is obtained, besides 3-pyridinol (21), the crystalline hydrochloride of l-amino-l,5-anhydro-l-deoxy-D-fhreo-pentulose hydrate (22). The crystalline hydrate exhibits no carbonyl band in its infrared and ultraviolet spectra. The water content cannot be removed without decomposition of the compound, and is, therefore, water of constitution. The nuclear magnetic resonance spectrum of 22 lacks the signal characteristic of an anomeric proton. The free ketone group is, however, detectable by the preparation of a (2,4-dinitrophenyl)-hydrazone. 

It is not requisite that the anion eliminated in the step 19 to 20 be a hydroxyl ion, because acid hydrolysis of 5-amino-5-deoxy-l,2-0-isopropylidene - 3 - O - (methylsulfonyl )-a- D -xylofuranose likewise yields 3-pyridinol (21). On subjection to acid hydrolytic conditions which remove the 2V-acetyl group, such N-acetyl derivatives as 5-acetamido-5-deoxy-a-D-xylopyranose (see p. 167) are immediately transformed, through 17, into 3-pyridinol (21). Furthermore, acid hydrolysis of methyl 5-acetamido-5-deoxy-2,3,4-tri-0-methyl-a-D-... 

The formation of the pyridinol is prevented if, in the step 19 to 20, no anion can be eliminated from C-3 this is the case with 5-amino-3,5-dideoxy-l,2-0-isopropylidene-a-D-er /thro-pentofuranose, which, on acid hydrolysis, afFords only the Amadori rearrangement product and no pyridine derivative. The reaction then proceeds, according to the above mechanism, in only one direction from 19. The 3-deoxypentose is prepared, in a manner analogous to the formation of 15, from 3-deoxy-l,2-0-isopropylidene-a-D-riho-hexofuranose through catalytic reduction of the phenylhydrazone of its periodate-oxidation product. ... 

The reaction of 5-amino-5-deoxy-l,2-0-isopropylidene-a-D-xylo-furanose (15) with methanolic hydrogen chloride (0.5 %), under careful exclusion of moisture, results in a mixture of the anomers of methyl 5-amino-5-deoxy-D-xylofuranoside, from which the /8-D anomer crystallizes. The five-membered ring-structure was proved by the results of periodate oxidation and by the infrared spectrum of the tetraacetate, which shows a band for NH. A methyl pyranoside was not found, and 3-pyridinol (21) was formed only in traces. A spontaneous ring-enlargement, such as is observed under similar conditions with 1,2-O-isopropylidene-5-thio-a-D-xylofuranose (see p. 208), is not possible in this instance. Stabilization as the methyl fiiranoside is, apparently, so rapid that the secondary reaction (leading to the pyranose form) does not occur. If water (several percent) is added to the reaction mixture, glycoside formation is hindered, and a large proportion of 3-pyridinol is formed. ... 

Cold barium hydroxide quantitatively removes the sulfite group from 25 and 26. The 5-amino-5-deoxy-D-xylose so liberated exists mainly in the form 17. Only in alkaline solution is it relatively stable toward acids it is extremely sensitive. Compound 17 accordingly behaves fundamentally differently from all other monosaccharides. In neutral solution (obtained by neutralization of its solution in barium hydroxide with carbon dioxide), the Amadori rearrangement product (22) is formed on standing at room temperature. With hydrochloric acid, 22 is likewise formed as the major product, together with 3-pyridinol (21). Free 17 cannot be isolated in pure form the product obtained contains 16 and 22 in proportions that vary with the pH of the evaporated solution. The impurities are lowest at pH 9.6. It is reported that, from the evaporated solution of 17, a 96 % yield of 25 can be recovered, but it should be mentioned that 16 and 22 also react with sulfurous acid to form 25 and 29. Thin-layer chromatograms (silica gel with p-dioxane—water) always show, besides 17, spots for the secondarily formed 16 and 22. 

Like the 5-amino aldopentoses, the 5-amino aldohexoses have a pronounced tendency to form the pyranose ring in alkaline solution. In acid solution, three molecules of water are eliminated per molecule, to give the corresponding derivative of 3-pyridinol. 5-Amino-5-deoxyaldohexopyranoses are, however, distinctly more stable, as the Amadori rearrangement and pyridine formation occur at pH 5.7—6.2. With the pentose analogs, these reactions begin at pH 7—8. Because of the reactive a-amino alcohol arrangement at C-1, the 5-amino-5-... 

Acid hydrolysis of 6-amino-6-deoxy-2,3-0-isopropylidene-I-0-p-tolylsulfonyl-a-L-3C /lo-hexulofuranose (77b) and of 1,6-diamino-1,6-dideoxy-2,3-0-isopropylidene-a-L- /lo-hexulose, obtained in a similar manner through the azido compound, gives 3-hydroxy-2-pyridine-methanol 2-p-toluenesulfonate and 2-(aminomethyl)-3-pyridinol, respectively. ... 

The pyranose 35 and the furanose 164 are stable in neutral solution at room temperature, and are separable by column chromatography without equilibration. On heating, or by acid catalysis (0.1 M hydrochloric acid, room temperature, 35 hours), an equilibrium between forms 35 and 164 is established. From the optical rotation, the ratio of the six-membered to the five-membered ring is calculated to be about 2 1. Alkaline catalysis causes very rapid attainment of equilibrium, but, simultaneously, decomposition occurs. The 5-acetamidopyranose 35 is, after attainment of its equilibrium, stable toward acids, and shows no dehydration reaction to form 3-pyridinol. However, under conditions in which the N-acetyl group is hydrolytically removed (heating with 2 M hydrochloric acid), 35 is transformed into 3-pyridinol through the intermediate formation of free 5-amino-5-deoxy-D-xylopyranose. ... 

A topic which has attracted a large research effort over the years is the determination of the precise structure of heterocyclic molecules which are potentially tautomeric - the pyridinol/pyridone relationship (2.2.4) is one such situation. In principle, when an oxygen is located on a carbon a or y to nitrogen, two tautomeric forms can exist the same is true of amino groups. 

Sodium dithionite can also be used as sulfonating agent in special cases, e.g., for iV-heterocyclic nitro compounds whose nitro groups are then simultaneously reduced to amino groups. 5-Amino-4-uracilsulfonic acid was thus prepared from 5-nitrouracil, and 3-amino-4-hydroxy-2-pyridinesulfonic acid from 3-nitro-4-pyridinol.196... 

Amino acid, 8-hydroxyquinoline, dipicoiinic acid and related complexes 6-Metkyl-2-pyridinolate and acetamide complexes Edta and related complexes Triaiene 1-oxide complexes N-S Ligands N- C Ligands... 

During Strecker degradation of [l-i CJ-D-glucose with primary a-amino acids, pyrroles and pyridinols are formed as major products (6). 4-Aminobutyric acid and peptide bound lysine are transformed into [i3CHO]-2-formyl-5-hydroxymethylpyrroles (9). Amino acids like Val, He, Leu, Phe and Met are transformed into 2-[i3cjjO]-pyrrole lactones (70). Equimolar amounts of cysteine (methionine) and [l(or 6)- C]-D-glucose were heated for 1,5 h at 160°C in aqueous solution at pH 5. The volatiles were extracted with pentane/ether and analyzed as described (7). In Table I selected (unlabeled) Strecker degradation products from cysteine and methionine are summarized. Pyruvat (1), 2- and 3-mercaptopropionic acids (2, 3) from cysteine as well as 2-oxo-5-thiahexanoic acid (4) and 5-thiahexanoic acid (5) from methionine. 

Oxidation of furfural with chlorine water or sodium hypochlorite followed by treatment of the product (see Section I.l.C,) with sulfamic acid gives 3-hydroxy-2-imino-l(2f0-pyridinesulfonic acid, which is converted to 2-amino-3-pyridinol(XI-275) on hydrolysis. ... 

Derivatives of 5-aminoaldoses have been partially characterized by conversion to 3-pyridinols. For example, 6-amino- and 6-nitro-5-acetamido-l,2-0-cyclo-hexylidene-5,6-dideoxy-L-iodofuranose and the corresponding D-glucofuranoses when boiled under reflux with hydrochloric acid form 6-aminomethyl- and 6-nitromethyl-3-pyridinol (Xn-281, R = NHj... 

Dihydro-1,2-diazabicyclo [3.2.0] -3-hepten-6-ones MI-312 and XII-313 and diazepinones XII-314 are readily interconvertible ring systemsand all three can give l-amino-3-pyridinol salts (see Section IV.3., p. 839) or 3-pyridinols. When heated in methanol, the 2-acetyl- or 2-benzoyl-derivative of MI-313 rearranges to several products including 6-acetamido- or 6-benzamido-3-hydroxy-4-methjd-5-phenylpyridine (XII-317) in 17% and 68% yield, respectively, presumably through intermediates such as XII-315 and... 

Halo-4-nitropyridines and their A -oxides react at the C-nitro group when treated with bases or alkoxides to give XII-357 or MI-358 (X = Cl, Br, I). However, 3-fluoro-4-nitropyTidine and its 1-oxide form 4-nitro-3-pyridinols and 4-nitro-3-alkoxypyridines, respectivelyThe 3-alkoxy-4-nitropyridine-l-oxides have been converted to 3,4-dialkoxypyridine-l-oxides. Because of this marked reactivity of the 3-fluoro substituent, these studies have been extended to 3-fluoro-5-methyl-4-nitropyridine-l-oxide, 3-fluoro-2-methyl-4-nitropyri-dine-l-oxide, and 2,6-dimethyl-3-fluoro-4-nitropyridine-l-oxide. Several of these fluoronitropyridines have been extensively studied as potential reagents for formation of amino acid derivatives. 2-Fluoro-3,5-dinitropyridine, a typical example, is hydrolyzed by hot water and reacts with hot alcohols to form 2-alkoxy-3,5-dinitropyridines and reacts with amino acids and their derivatives to give well-defined products. The reactions of a number of fluoronitropyridines and their N-oxides have been summarized by Talik and Talik and the relative reactivities toward simple nucleophiles have been observed, as shown on p. 689. 

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