Methyladenines

Polarized IR spectra in PVA film, and the calculated (SCRF) spectra of 7-methyl- and 9-methyladenine, 17 and 18 (R = Me) respectively, have demonstrated that they exist as the amino forms shown [97JPC(A)4361],... 

Methyl thioacetnte, electrostatic potential map of, 791 9-Methyladenine. electrostatic potential map of, 1121 Methylamine, bond angles in. 19 dipole moment of, 39 electrostatic potential map of, 56, 922... 

The bulk effect of water as a solvent is rather dramatic since it causes a drastic reduction of the nucleophilicity of 9-methyladenine N1 and even more of 9-methylguanine 06. As a result, there is a reversal of the nucleophilicity order of the purine bases passing from gas phase to aqueous solution. In fact, in solution, methyladenine is more nucleophilic than methylguanine. Moreover, oxygen and N7 nucleophilic centers of 9-methylguanine compete almost on the same footing in solution (Table 2.2) and also the reactivity gap between N1 and N7 of 9-methyladenine is highly reduced in comparison to the gas phase. 

SCHEME 2.5 Reaction pathways for 9-methyladenine alkylation by o-QM, investigated by DFT. 

Regarding product stability, DFT calculations predict that only two of the adducts of o-QM with 9-methyladenine, QM-A1 and QM-A6 are lower in energy than reactants, both in the gas phase and in water (Table 2.3). However, the adduct at N1 (QM-A1) can easily dissociate in aqueous solution, exhibiting an activation energy for the reversal of the benzylation process of 19.7 kcal/mol. 

TABLE 2.3 Stability of the QM-9-Methyladenine and QM-9-Methylguanine Adducts (QM-A and QM-G, Respectively) Relatively to Reactants in the Gas Phase (AGgas) and in Aqueous Solution (AGaq). Activation Energies for Their Decomposition into Free QM and Cytosine (AG e )... 

Liihrs DC, Viallon J, Fischer I (2001) Excited state spectroscopy and dynamics of isolated adenine and 9-methyladenine. Phys Chem Chem Phys 3 1827... 

Treatment of cordycepin with nitrous acid, and subsequent hydrolysis of the deaminated product, yields hypoxanthine, indicating that in the adenine moiety the primary amino group is free and the glycosidic linkage involves C7 or C9. The close similarity between the ultraviolet absorption spectrum of cordycepin and those of 9-methyladenine and adenosine63 (9-/3-J>-ribofuranosyladenineMa) favors the latter possibility. The complete stereoisomeric description of cordycepin (XXVIII), formulation of which... 

Figure 12. Methyladenine - Methylthymine (AT) and Methylcytosine - Methyl-guanine (CG) base pairs. The dipole moments of the isolated bases and of the base pairs are also shown.

Figure 13. Selected frequency assignments for methyladenine, both in complex (top) and isolated (bottom). The values of the shift due to complexation are also given.

Example 57 the synthesis of 2-chloro-iV -methyladenine-9-(2-methyl-propyl)bis phosphonate, analogous to the corresponding bisphosphate, has been performed by Jacobson and associates [93]. The key step in this synthesis is the Arbuzov-Michaelis reaction. 

---