Substituted Hypoxanthine, Adenine, and Guanine Derivatives

1 Substituted Hypoxanthine, Adenine, and Guanine Derivatives Chemistry 

The iV- and C-atoms of the purine ring system of hypoxanthine, adenine and guanine, as well as the amino groups of these compounds carry additional substituents in several secondary products. Most frequently methyl groups, but also isoprenoid groupings, CHgS-groups and threonine residues may be present (Table 45 and Fig. 175). 

N-Methyl-N -threonino- N- Dime thy tally 1-2-carbonyl adenine methylthioadenine 

Methylated purines (and pyrimidines, cf. D 16.1) are constituents of the different nucleic acid species of all groups of organisms. Rich in methylated purines is tRNA which contains also purines with other substituents (Table 45). In addition, methylated and isoprenylated purines occur in the free state. The methylated purines caffeine, theobromine, and theophylline (Fig. 176) are synthesized in higher plants, isoprenylated purines of the zeatin type are formed in microorganisms, plants and animals and the methylated purines given in Fig. 175 were found in the free state in animal tissues and in the urine (E 1). 

Alkylations and other types of transformation may, however, also proceed with free purines. In Dictyostelium for instance, dimethylallyl pyrophosphate condenses with AMP to produce isopentenyl adenine. In mammalian tissue 3-methyladenine is formed from adenine, and in plants theobromine and caffeine 

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Table 45. Substituted hypoxanthine, adenine and guanine derivatives found in RNA-species...

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