Purine Carboxylic Acids

Here again, comparitively little systematic information is available, but a parallel with pyridine a-acids can again be implied in that purine acids undergo decarboxylation on heating.  

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Oxo- (Hydroxy-) and Alkoxypurines 7 Thioxo- and Selenoxopurines and Derivatives 8 The Amino- (and Amino-oxo)purines 9 The Purine Carboxylic Acids and Related Derivatives 10 Nitro-, Nitroso-, and Arylazopurines 11 Purine N-Oxides Ch. 12 The Reduced Purines... 

H-Pyrido[2,l-i]purine-9-carboxylic acid, 7-oxo-methyl ester, 5, 566 Pyrido[2,3-6]pyrazine, amino-nucleophilic attack, 3, 253 Pyrido[2,3-h]pyrazine, 6-chloro-reactions... 

The analytical data obtained, particularly by the PUMA mass spectrometer on board Vega 1 during the flyby, indicate the presence of a large number of linear and cyclic carbon compounds, such as olefins, alkynes, imines, nitriles, aldehydes and carboxylic acids, but also heterocyclic compounds (pyridines, pyrroles, purines and pyrimidines) and some benzene derivatives no amino acids, alcohols or saturated hydrocarbons are, however, present (Kissel and Krueger, 1987 Krueger and Kissel, 1987). 

A regiospecific strategy to A-7-substituted purines 65 and its application to a library of 2,6,8-trisubstituted purines has been reported. The three-step synthetic strategy involves cyclization reactions of suitably substituted pyrimidines 63 with either a carboxylic acid or an aldehyde <06JC0410>. 

Shaw and co-workers during studies into the de novo biosynthesis of purine nucleotides demonstrated that 4(5)-aminoimidazole (25 R = H) on treatment with a saturated aqueous solution of potassium bicarbonate at 70°C for 15 min gave 4-aminoimidazole-5-carboxylic acid (38) in an estimated yield of 40% [71JCS(C)1501]. This and related reactions are discussed in more detail in Section V,B,4. 

Ring opening of 97 as indicated gives the 9-(a-amino-Q -phenylmethyl) purine 98, which by a base-catalyzed elimination of benzylideneimine is converted into 6,8-diphenyl-2-methylthiopurine 99. This pteridine-purine transformation has a close resemblance to the enzyme-catalyzed ring contraction of tetrahydropteridine into xanthine-8-carboxylic acid (64MI1), in which reaction it was proved by radioactive labeling that it is exclusively C-7 that is expelled. 

From 133-tiiazines 23 and 5-amino-4-imidazole-carboxylic acids 24 a variety of purines and purine nucleosides 25 have been prepared via an inverse electron demand Diels-Alder reaction <99JA5833>. 

Photochemical reactions of the purines and pyrimidines assume special significance because of the high molar extinction coefficients of the nucleic acids present in cells. Light is likely to be absorbed by nucleic acids and to induce photoreactions that lead to mutations.190 Both pyrimidines and purines undergo photochemical alterations, but purines are only about one-tenth as sensitive as pyrimidines. Photohydration of cytidine (Eq. 23-25) is observed readily. The reaction is the photochemical analog of the hydration of a,P-unsaturated carboxylic acids. Uracil derivatives also undergo photohydration. 

H,6H-Purine, l,7-dimethyl-6-oxo-UV spectra, 5, 517 7H,8H-Purine, 8-oxo-UV spectra, 5, 517 Purinecarboxamides reactions, 5, 550, 551 Purinecarboxylic adds reactions, 5, 550 Purine-6-carboxylic acids synthesis, 5, 593 Purine-8-carboxylic acids synthesis, 5, 593 Purine nucleotides biosynthesis, 1, 87-88 Purine[9,8-a]quinolines, 5, 566 Purines, 5, 499-605 aldehydes reactions, 5, 549 synthesis, 5, 593 alkylation, 5, 505, 528-538 amination, 5, 541-542 anions... 

Aldehyde oxidase catalyzes the oxidation of aldehydes to carboxylic acids by dioxygen, but also catalyzes the hydroxylation of pyrimidines. Despite its rather broad specificity for substrates, it may well be that aldehyde oxidase should be regarded primarily as a pyrimidine hydroxylase. Thus, xanthine oxidase and aldehyde oxidase catalyze the hydroxylation of purines and pyrimidines respectively. The oxygen incorporated into the product comes from water, not 02. The dioxygen serves as the electron acceptor and other oxidizing agents may be used. 

CP608039 (2S,3S,4R,5R)-3-amino-5 6-[5-chloro-2-(3-methylisoxazol-5-yhnethoxy)benzylamino]purin-9-yl-l-4-hydroxytetrahydrofuran-2-carboxylic acid methylamide... 

Although molybdenum and tungsten enzymes carry the name of a single substrate, they are often not as selective as this nomenclature suggests. Many of the enzymes process more than one substrate, both in vivo and in vitro. Several enzymes can function as both oxidases and reductases, for example, xanthine oxidases not only oxidize purines but can deoxygenate amine N-oxides [82]. There are also sets of enzymes that catalyze the same reaction but in opposite directions. These enzymes include aldehyde and formate oxidases/carboxylic acid reductase [31,75] and nitrate reductase/nitrite oxidase [83-87]. These complementary enzymes have considerable sequence homology, and the direction of the preferred catalytic reaction depends on the electrochemical reduction potentials of the redox partners that have evolved to couple the reactions to cellular redox systems and metabolic requirements. 

More reactive than HMDS (see below) or TMCS, but forming essentially similar derivatives useful for alcohols, amines, amino acids, carboxylic acids, penicillic acid, purine and pyrimidene bases... 

Chemical Name 3-Pyridine carboxylic acid compounded with 3,7-dihydro-7-[2-hydroxy-3-[(2-hydroxymethyl)methylamino]propyl]-l,3-dimethyl-lH-purine-2,6-dione (1 1)... 

On the basis of several analytical studies (differential thermal analysis, fluorescence, CPMAS solid-state NMR spectroscopy and others) [56-58] two models have been proposed to describe the structure of HCN-polymers, the Umemoto [59] and the Volker models [60]. In the Volker model, HCN polymerizes to extensive double-ladder rod-like structures, while a simpler mono-ladder pattern was hypothesized by Umemoto (Fig. 1). Irrespective of the structure assumed by HCN-polymers, a large panel of purine, imidazole and pyrimidine derivatives can be obtained by hydrolysis of these materials. In 1963, Lowe described the first example of acidic hydrolysis of the HCN-polymer (boiling 6.0 N HC1) to yield amino acids, carboxylic acids, adenine and hypoxanthine (Scheme 4). 

A cursory glance at the structure of DNA shows that it is composed of hydrogen-bonded units, the purine and pyrimidine bases, attached to sugars that are linked by phosphate groups. There is no chemical reason why the perfectly symmetric phosphates should bind in the orientation that they do. The same problem arises in when a synthetic analogue of a DNA-type replicator is considered. The most useful linkages are imine and peptide bonds. Both require a terminal amine the former results from a reaction with an aldehyde and the latter with an activated carboxylic acid. The problem that occurs is that if these functional groups are present within the same molecule self-polymerization may occur unless a substantial effort is made to avoid this. 

Aldehyde Oxidase. This enzyme is usually found in similar locations to xanthine oxidase or dehydrogenase and has been isolated from insects, birds, and mammals (20, 21). Aldehyde oxidase seems to be a poor choice of name for this enzyme because, while it oxidizes aldehydes to carboxylic acids, it also accepts a variety of purines and pyrimidines as oxidizable substrates. For example, aldehyde oxidase catalyzes the conversion of 2-hydroxypyrimidine to uracil and of adenine to 8-hydroxy-adenine (25). It appears that xanthine oxidase and aldehyde oxidase are... 

In comparison to butyric acid, the microenvironment of the carboxylic acid in 49 alters its complexation efficiency and the preferred geometry of its adenine complex. The nucleoside selectivity is also altered and improved to the extent that 49 can be considered a moderately selective host. As seen in Table 6 (entries 8-11), 49 selectively binds purines, with the association constants following the order A (56) > G (57) > (58) C Si (59) U. The maximum selectivity is AAG° = 2.8 kcal mol-1, while for butyric acid the selectivity was MejG Si C A U with only 1.3 kcal mol-1 separating the strongest and weakest complexes [52],... 

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