Pteridine 2,4-dihydroxy

The molecular features of covalent hydration are also present in the dihydroxy series, i.e., in pteridine-2,6-dione (30) and in pteridine-4,6-dione. The latter compound is hydrated only at the C(7)—N(8) double bond, whereas (30) forms two hydrated species, 7-hydroxy-7,8-dihydro- (29) and 4-hydroxy-3,4-dihydro-pteridin-2,6-dione (31) (equation 8). Structure (29) is thermodynamically the more stable substance (31) is formed more rapidly in solution but disappears slowly with time (63JCS5151). Insertion of a 4-methyl group greatly reduces the extent of 3,4- in favour of 7,8-hydration by a blocking effect . 

The structures of many polyhydroxypteridines have been investigated by Pfleiderer and his associates. Although 2,4-dihydroxy-pteridine (lumazine) appears to exist mainly in the dioxo form 182,... 

The situation in the pteridine series is somewhat more complex. Pteridine, 2-, 4-, and 7-hydroxypteridine, and some of the dihydroxy-pteridines are oxidized, stepwise and quantitatively, in the presence of xanthine oxidase to a single substance, 2,4,7-trihydroxypteridine. Notably, 6-hydroxypteridine, which readily forms a covalent hydrate, is not attacked. 

In systems such as the 2- and 6-hydroxypteridine series, rapid potentiometric or spectrophotometric pA determinations on neutral solutions usually give values near to the acidic pA of the hydrated series. (Exceptions include 2-hydroxy-4,6,7-trimethyl-, 6-hydroxy-7-methyl-, and 4,6-dihydroxy-pteridine, where the neutral solution contains comparable amounts of hydrated and anhydrous species. In such cases, rapid potentiometric titrations show two well-defined and separated curves, one for the hydrated, the other for the anhydrous, species.) Similarly, from solutions of the anion, an approximate pA value for the anhydrous species is obtained. For convenience, the anhydrous molecule is referred to as HX, its anion as X , the hydrated neutral molecule as HY, and its anion as Y, and the two equilibrium constants are defined as follows ... 

Pteridine-6-carboxylic acid, 4,7-dihydroxy-properties, 3, 277 Pteridine-6-carboxylic acid, 7-oxo-synthesis, 3, 310... 

Dihydroxy-7-methyl- pteridine NaOH/190° 2-Carboxy-3-hydroxy-S nethyl and 3-amino-2-carboxy-5 -methyl 434... 

Dihydroxy-6,7-dimethy 1-pteridine NaOH 2-Amino-3-carboxy-5,6-dimethyl 420, 433... 

Dihydroxy-6,7-diphenyl- pteridine Piperidine 2,3 -Diphenyl-5 -piperidino-caibonyl-6-piperidino-carbonylamino and 2-amino-5,6-diphenyl-3-piperidinocarbonyi 451... 

Dihydroxy-6,7 -dipheny l-pteridine BuNHj 2-Amino-3(butylcarbamoyl)-5,6-diphenyl 455... 

Dihydroxy-6,7-diphenyl- pteridine HOCHjCH,NH, 2-Amino-3-(d-hydroxyethyl-carbamoy l)-5,6-diphenyl 451... 

Hydroxy-pteridine werden am besten uber Palladium/Kohle in 0,1 n Natronlauge hydriert, wobei 4-Hydroxy- sowie 2,4-Dihydroxy-pteridin in 2-Hydroxy- bzw, 2,4-Dihydr-oxy-5,6,7,8-tetrahydro-pteridin iibergehen. (Sind die Sauerstoff-Funktionen in 2- und 4-Stellung durch 1- und 3-Alkylierung als Carbonyl-Gruppen festgelegt, so hydriert man mit... 

Biopterin (9.27), an ivory-coloured pteridine, biosynthesized by animals and widely distributed in Nature, is L-erythro-2-amino-4-oxo-6-( 1,2-dihydroxy-propyl) pteridine. Once again, GTP is the precursor. A reduced form, 5,6,7,8-tetrahydrobiopterin is the co-factor required for the set of enzymes that use... 

For a long time before the ring structure of pterins was known, compounds containing the pteridine ring were being prepared. In 1895, 2,4-dihydroxy-pteridine was prepared by oxidation of tolualloxazine and decarboxylation of the resulting 2,4-dihydroxypteridine-6,7-dicarboxylic acid, and the same compound was prepared in 1907 by the action of hypobromite on pyrazine-2,3-dicarboxamide. The condensation of 4,5-diaminopyrimidine and benziF to form 6,7-diphenylpteridine reported in 1906 was the first example of the most versatile general method of pteridine synthesis. 

The cyanides 1408-1412 have all been synthesized by dehydrating their carbox-aldoximes with acetic anhydride [1070-1074]. A pteridine synthesis yielded 75% of 6-cyano-l,3-dimethyUumazine 1408 [1070]. N-Acetyl (3-phenyl-l,2,4-triazolo-5-yl)-thiolacetonitrile 1409 was obtained as the condensation product from a triazole derivative and chloro acetaldehyde, followed by oximation and dehydration, in 79% yield [1071]. endo-l-Cyano-3-acetoxy-8-oxabicyclo[3.2.1]oct-6-ene 1410 (89%) is an intermediate in the synthesis of ll-oxatricyclo[5.3.1.0 Jundecane [1072]. A synthesis of loi,25-dihydroxY-18-norvitamin Dj and la,25-dihydroxy-18,19-dinorvitamin Dj requires the 8j8-acetoxy-des-A,B-cholestane-18-nitrile 1411 (86%) [1073]. A new route to spirooxindoles, a tricyclic system found in a number of interesting natural products, requires the cyanide 1412 (72%) as a key intermediate [1074]. 

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