Pterin 8-Oxide

A suspension of pterin 8-oxide 1 in a 1 1 mixture of TFA-TFAA was stirred for 1 hour at 50°C. The solvent was then evaporated and the residual solid hydrolysed with ammonium hydroxide/sodium hydroxide solution. Acidification gave xanthopterin 2 in quantitative yield. 

An excellent method for the preparation of gem-difluoro compounds from aldehydes and ketones consists of conversion of the carbonyl compound to the corresponding 1,3-dithiolane followed by treatment with two equivalents of l,3-dibromo-5,5-dimethylhydantoin (DBH) and pyridinium poly(hydrogen fluoride) (HF-pyridine) in methylene chloride. Attempted extension of this procedure to 7-methoxy-2,2-dimethyl-4-chromanone, however, gave only the dihydro- 1,4-dithiin derivative 1 in 78% yield. This transformation, which proceeded in excellent yield with a variety of 4-chromanones, was found to require only the DBH (i.e. fluoride ion played no role). 

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Treatment of pterin 8-oxide (15) with a mixture of trifluoroacetic acid and its anhydride under mild conditions provides a facile synthesis of xanthopterin (16) (95—100 %) (see Scheme 11). Analogous rearrangement of 2,4-diaminopteridine 8-oxide (17) takes place under more forcing conditions, but methyl substitution in the 6-position of compounds (15) and (17) effectively blocks the rearrangement,... 

Pterin 8-oxides, - 24,437 Purine ring opening, oxidative 24, 241 Purines... 

Pterin 8-oxide allowed to react with trifluoroacetic anhydride-trifluoroacetic acid followed by basic hydrolysis xanthopterin. Y 95-100%. F. e. s. E. C. Taylor and P. A. Jacobi, Am. Soc. 95, 4455 (1973). 

New syntheses of 6-chloropterin (266) and 6-formylpterin (269) have been elaborated. The chloro-compound is available in one step by the action of acetyl chloride in trifluoroacetic acid on pterin 8-oxide (265), whereas the aldehyde is the product of the multi-stage process outlined in Scheme 62, the first stage of which is the production of the pyrazine-aldehyde (268) by a Krohnke aldehyde synthesis on the chloromethyl derivative (267). The chloropterin condenses easily with arylthiols and alkyl mercaptans, but not with alkylamines. 

Stronger chemical evidence for the presence of a dithiolene in molybdopterin was obtained when the mild alkylation reagent iodoacetamide effectively trapped the dithiolene (65). This reaction yielded a derivative whose characterization by FAB mass spectrometry and nuclear magnetic resonance (NMR) was consistent with the structure shown in Fig. 5. The method appeared to leave the side chain intact and preserved the pterin oxidation state. From this experiment the view persisted that molybdopterin is a disubstituted dithiolene bearing a reduced pterin and a short chain terminated with a phosphate. 

The presence of a pterin moiety in mononuclear Mo enzymes has stimulated work in this area. Concensus has replaced earlier confusion and controversy concerning the formulations, metal and pterin oxidation states, and electronic descriptions of Mo—pterin complexes. High-valent, monomeric oxo—Mo pterin complexes are diamagnetic yet they are formulated, on the basis of X-ray photoelectron and NMR spectroscopic data, as Mov species This formulation and (partial) representations like (265) and (266) attempt to reflect the extent of electron pair delocalization in these non-innocent (buffered588) systems, not the existence of metal- and pterin-based diradicals.630... 

Oxidative substitutions at ring junction positions in various tetrahydro-5-deaza-pterins (79JA6068) and -flavins (77JA6721) have been studied, e.g. to give (13), and the oxidation-reduction reactions of 5-deazaflavins (e.g. 78CL1177, 80CPB3514) across the 1,5-positions, e.g. (19) (20), are involved in their co-enzymic role in enzymic oxidations (see Section... 

AT-Oxidation is very sensitive to steric effects, since 1-substituted lumazines and pterins give only 5-oxides and the presence of bulky substituents at position 7 also directs oxidation to N-5. The pteridine 5-oxide (52) and 8-oxide (53) and the 5,8-dioxide (55) contain the AT-oxide groups as such, even when the possibility of AT-hydroxy tautomers exists, as in (53) i(54). 

The action of sulfur nucleophiles like sodium bisulfite and thiophenols causes even pteridines that are unreactive towards water or alcohols to undergo covalent addition reactions. Thus, pteridin-7-one smoothly adds the named S-nucleophiles in a 1 1 ratio to C-6 (65JCS6930). Similarly, pteridin-4-one (73) yields adducts (74) in a 2 1 ratio at C-6 and C-7 exclusively (equation 14), as do 4-aminopteridine and lumazine with sodium bisulfite. Xanthopterin forms a 7,8-adduct and 7,8-dihydropterin can easily be converted to sodium 5,6,7,8-tetrahydropterin-6-sulfonate (66JCS(C)285), which leads to pterin-6-sulfonic acid on oxidation (59HCA1854). 

Various 6- and 7-methyl- and 6,7-dimethyl-pteridines bearing either oxo or amino groups in the 2- and 4-positions can be oxidized to the corresponding carboxylic acids by alkaline potassium permanganate on heating. Various lumazine and pterin mono- and di-carboxylic acids have been prepared in this way (48JA3026, 78CB3790). 

Another unusual rearrangement is performed by Bacillus subtilis during the catabolism of sepiapterin (237), in converting the whole side-chain with subsequent oxidation of the pyrazine ring into 6-(l-carboxyethoxy)pterin (238 equation 75). 

Pterin, 6-hydroxymethyl-7,7-dimethyl-7,8-dihydro-bacteriostatic activity, 3, 325 Pterin, 1-methyl-hydrolysis, 3, 294 5-oxide... 

Pterin, 6-methyl-5,6,7,8-tetrahydro-configuration, 3, 281 conformation, 3, 281 Pterin, 6-oximinomethyl-8-oxide... 

The aldehyde oxidoreductase from Desulfovibrio gigas shows 52% sequence identity with xanthine oxidase (199, 212) and is, so far, the single representative of the xanthine oxidase family. The 3D structure of MOP was analyzed at 1.8 A resolution in several states oxidized, reduced, desulfo and sulfo forms, and alcohol-bound (200), which has allowed more precise definition of the metal coordination site and contributed to the understanding of its role in catalysis. The overall structure, composed of a single polypeptide of 907 amino acid residues, is organized into four domains two N-terminus smaller domains, which bind the two types of [2Fe-2S] centers and two much larger domains, which harbor the molybdopterin cofactor, deeply buried in the molecule (Fig. 10). The pterin cofactor is present as a cytosine dinucleotide (MCD) and is 15 A away from the molecular surface,... 

Pterins — These are pigments derived from pteridine skeletons. All natural pterins are 2-amino-4-hydroxypteridines bearing various substituents at Cg and C7 and having different oxidation states of N5 and Ng. 

Gieseg, S.P., Maghzal, G., and Glubb, D., Protection of erythrocytes by the macrophage synthesized antioxidant 7,8 dihydroneopterin. Free Radic. Res., 34, 123, 2001. Gieseg, S.P. and Cato, S., Inhibition of THP-1 cell-mediated low-density lipoprotein oxidation by the macrophage-synthesised pterin, 7,8-dihydroneopterin, Redox Rep., 8, 113, 2003. 

Chordate neurons (early Cambrian) As above plus first hydroxylations giving serotonin and dopamine iron/pterin chemistry in cytoplasm vesicle filled in centre of cell Recovery by amine oxidation (flavoenzymes)... 

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