Purine transformation

In a report dealing with the synthesis and anticancer activity of (6 -substituted)-7- and 9-(2,3-dihydro-5i/-l,4-benzodioxepin-3-yl)purines, transformations of V9 -alkyl-6 -halopurines have been described <06T11724>. 

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. 

These organisms have been used frequently in the elucidation of the biosynthetic pathway (37,38). The mechanism of riboflavin biosynthesis has formally been deduced from data derived from several experiments involving a variety of organisms (Fig. 5). Included are conversion of a purine such as guanosine triphosphate (GTP) to 6,7-dimethyl-8-D-ribityUuma2ine (16) (39), and the conversion of (16) to (1). This concept of the biochemical formation of riboflavin was verified in vitro under nonen2ymatic conditions (40) (see Microbial transformations). 

Purine, 2-methylthio-6,8-diphenyl-ring transformations, 3, 308 Purine, 9-methyl-6-thiomethyl-dipole moments, 5, 521... 

Polar functional groups such as alcohols or phenols 11 or trimethylsilanol 4 are transformed by monofunctional silylating reagents Me3SiX 12 into their hpophilic and often volatile trimethylsilyl ethers 13 whereas water is converted into persilyl-ated water (=Me3SiOSiMe3, hexamethyldisiloxane, HMDSO, 7, b.p. 100 °C). The persilylation of phenols and, in particular, catechol (or hydroquinone) systems (Scheme 2.1) protects them efficiently against air oxidation even at temperatures of up to 180 °C. (cf, e.g., the silylation-amination of purine nucleosides with dopamine hydrochloride in Section 4.2.4)... 

Conventional use has been made of the radioisotope C, and details need hardly be given here. Illustrative examples include the elucidation of pathways for the anaerobic degradation of amino acids (Chapter 7, Part 1) and purines (Chapter 10, Part 1). Some applications have used C with high-resolution Fourier transform NMR in whole-cell suspensions, and this is equally applicable to molecules containing the natural or the synthetic P nuclei. As noted later, major advances in NMR have made it possible to use natural levels of C. 

Steenken, S. (1989). Purine bases, nucleosides and nucleotides aqueous solution redox chemistry and transformation reactions of their radical cations and e" and OH adducts. Chem. Rev. 89, 503-520. 

With the death of the bean, cellular structure is lost, allowing the mixing of water-soluble components that normally would not come into contact with each other. The complex chemistry that occurs during fermentation is not fully understood, but certain cocoa enzymes such as glycosidase, protease, and polyphenol oxidase are active. In general, proteins are hydrolyzed to smaller proteins and amino acids, complex glycosides are split, polyphenols are partially transformed, sugars are hydrolyzed, volatile acids are formed, and purine alkaloids diffuse into the bean shell. The chemical composition of both unfermented and fermented cocoa beans is compared in Table 1. 

However, the biochemical significance of the latter studies is challenged by the fact that the transformation of transient purine and pyrimidine radicals into diamagnetic decomposition products is oxygen-independent in the solid state. Therefore, it is necessary to study the chemistry of one-electron nucleobase intermediates in aerated aqueous solutions in order to investigate the role of oxygen in the course of reactions that give rise to oxidation products within DNA and model compounds. In this respect, type I photo-... 

The two overwhelming oxidation products of the purine moiety of dGuo 37 arising from the transformation of guanine radical cations 38 were isolated and identified as 2,2-diamino-4-[(2-deoxy-/l-D-eryfhro-pentofura-nosyl)amino]-5(2H)-oxazolone (41) and its precursor 2-amino-5-[(2-deoxy-... 

Two types of addition to pyrimidine bases appear to exist. The first, the formation of pyrimidine photohydrates, has been the subject of a detailed review.251 Results suggest that two reactive species may be involved in the photohydration of 1,3-dimethyluracil.252 A recent example of this type of addition is to be found in 6-azacytosine (308) which forms a photohydration product (309) analogous to that found in cytosine.253 The second type of addition proceeds via radical intermediates and is illustrated by the addition of propan-2-ol to the trimethylcytosine 310 to give the alcohol 311 and the dihydro derivative 312.254 The same adduct is formed by a di-tert-butyl peroxide-initiated free radical reaction. Numerous other photoreactions involving the formation by hydrogen abstraction of hydroxyalkyl radicals and their subsequent addition to heterocycles have been reported. Systems studied include 3-aminopyrido[4,3-c]us-triazine,255 02,2 -anhydrouri-dine,256 and sym-triazolo[4,3-fe]pyridazine.257 The photoaddition of alcohols to purines is also a well-documented transformation. The stereospecific addition of methanol to the purine 313, for example, is an important step in the synthesis of coformycin.258 These reactions are frequently more... 

A general and efficient solid-phase synthesis of A-9-substituted 2,8-diamino purines 62 has been described. The key synthetic transformation uses a carbodiimide-mediated cyclization of a thiourea 60. The reaction was performed using microwave reaction conditions on solid phase <06TL8897>. 

A rapid access to carbocyclic nucleosides, containing a fused isoxazoline ring has been proposed, starting from cyclopentadiene. The route involves a het-ero Diels-Alder cycloaddition reaction of nitrosocarbonylbenzene followed by a 1,3-dipolar cycloaddition of nitrile oxides, cleavage of the N-0 tether and transformation of the heterocyclic aminols into nucleosides via construction of purine and pyrimidine heterocycles (457). 

Those nucleosides found in the nucleic acids DNA and RNA involve the joining of ribose of deoxyribose to a purine or a pyrimidine base. One such nucleoside is adenosine, in which a nitrogen of adenine is linked to carbon 1 of the pentose, ribose. In this form it is a component of RNA but as a phosphory-lated derivative of adenosine (e.g. ATP), which is a high energy compound, it fulfils an important role in metabolism. The dinucleotides NAD and NADP are two cofactors necessary for many enzymic transformations and these also contain /V-glycosides of ribose phosphate. Other important nucleosides are found... 

Comparing electrochemical behavior and biological transformations of purine bases, Japanese chemists (Yao and Musha 1974, Ohya-Nishiguchi et al. 1980) have considered the anion-radicals of purine, its 8-deutero and 6,8-dideutero derivatives. As it turned out, up to 40% of the total spin density is localized in position 6 of the purine anion-radical (see Scheme 3.7). Ohya-Nishiguchi et al. (1980) noted that such a large localized spin density is very rare in a n electron system of the purine s size and should have important application in relation to its chemical reactivity. Protonation should... 

The synthesis of 9-(l,4-dihydroxybut-2-oxy)purines commenced with 2-butene-l,4-diol (1004) and via 1005 to 1006, which upon reaction with 1007 gave 1011 and then, upon hydrolysis, the racemic alkoxyamine 1012. The chiral derivatives commenced with the enantiomers of malic acid (1009) through 1010 to 1008, as shown in the scheme. Treatment of 1012 with 996 and further transformations followed almost the same sequence as before to give 1013. 

These compounds inhibit synthesis of purine nucleotides, which are made up of purine bases and phosphorylated ribose. Both compounds must be transformed into nucleotides by adding a phosphoribosyl fragment. 

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