Isoguanine

Deamination, Transamination. Two kiads of deamination that have been observed are hydrolytic, eg, the conversion of L-tyrosiae to 4-hydroxyphenyUactic acid ia 90% yield (86), and oxidative (12,87,88), eg, isoguanine to xanthine and formycia A to formycia B. Transaminases have been developed as biocatalysts for the synthetic production of chiral amines and the resolution of racemic amines (89). The reaction possibiUties are illustrated for the stereospecific synthesis of (T)-a-phenylethylamine [98-84-0] (ee of 99%) (40) from (41) by an (5)-aminotransferase or by the resolution of the racemic amine (42) by an (R)-aminotransferase. 

Purines — These molecules have basic skeletons of purine heterocycles. Adenine and guanine, intrinsic components of nucleic acids, are also ubiquitous molecules. Related molecules are isoguanine, xanthine, and uric acid. 

Since the formation of the isoguanine derivative 88 has been proved to occur via the intermediacy of 4-ureido-5-cyano-l-methylimidazole (87) (having as precursor the C-2 adduct), its formation can thus be described as oc-... 

Isoguanine (94), which is found in Prioneris wings along with hypoxanthine (92), xanthine (91), and uric acid (95), shows antineoplastic activities (Table VI) (57). Isolation of urocanic acid (137) from this wing material represents the first detection of this histidine derivative in an arthropod (Table VIII). A nonpteridine pigment, xanthommatin (58) (cf. Section II,B,l,b), is found in the larval body of Pieris brassicae (Table V). 

Figure 3.4 Representation of the main tautomeric forms of isoguanine in the gas phase and in aqueous solution. The relative stabilities (kcal moT j in the gas phase and in water are given in plain text and in italics, respectively.

Besides guanine and isoguanine, other nucleic acids bases are also found to be able to form the tetrad structures through H-bonds between the neighboring bases [24-27]. 

J. Gu, J. Leszczynski, Isoguanine From base pair to tetrad. J. Phys. Chem. A107, 9447-9455 (2003)... 

J. Gu et al., Isoguanine octamer From bowl to ball. Chem. Phys. Lett. 445, 243-245 (2007)... 

This chemical procedure was found to be of general applicability and a large panel of purine derivatives, namely hypoxanthine 2, diaminopurine 3, xanthine 4, isoguanine 5 and guanine 6 were obtained from the imidazole intermediates in the presence of other one-carbon fragments such as cyanide and cyanogens (Scheme 2). 

In addition to its occurrence as a component of ribonucleic acid D-ribose has been found in combination with uric acid in the blood12 and with 2-hydroxy-6-aminopurine (isoguanine) in the croton bean (Croton tiglium L).13-14 v. Euler, Karrer and Usteri15 as well as Schlenk16 have shown D-ribose to be a component of cozymase. 

Figure 8.7 Formation pathways of various purine derivatives (a) guanine, (b) hypoxanthine, (c) xanthine, (d) diaminopurine, (e) isoguanine, and (f) adenine...

The keto/enol or amino/imino equilibrium can be shifted, however, if the bases are chemically modified as in isoguanine (2-hydroxy,4-amino-purine). In this molecule, the tautomeric equilibrium depends largely on the dielectric constant of the solvent [525]. 

The naturally occurring purines fall into 4 main groups. (1) Simple substituted derivatives of purine (1) such as adenine (2) and various 6-AT-substituted derivatives. (2) Monoxo-dihydropurines such as hypoxanthine (3), guanine (4), and isoguanine (5). f3) Dioxotetra-hydropurines such as xanthine (6) and methylated derivatives including the 3,7-dimethyl derivative theobromine (7), 1,3-dimethylxanthine or theophylline f8), and 1,3,7-trimethylxanthine or caffeine (9). (4) Trioxohexahydropurines such as uric acid (10). 

In contrast to 6-aminopurines, several 8-aminopurines form stable 8-diazopurines with nitrous acid, especially when dipolar forms are possible. Thus 8-aminoxanthine and nitrous acid at 5-10 °C gave the 8-diazo derivative (188) (60JA3773) and similar products are produced from hypoxanthine, isoguanine and theophylline. In contrast 8-amino-9-methylxanthine failed to produce a stable diazo derivative and this tends to favour the particular ionic structure (188) which is further confirmed by the absence of imidazole imino groups in the IR spectra of these compounds. 

Adenine 1-oxide Adenine + isoguanine UV light 64B880... 

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