Synthesis of Some 2'-C-Alkyl Derivatives of 9-(2-Phosphonomethoxyethyl)adenine and Related Compounds

To study the effect of β-substitution in 2'-alkyl derivatives of 9-(2-phosphonomethoxyethyl)adenine (Ia) on the antiviral activity or group specificity, these derivatives were synthesized. 9-(2-Hydroxyalkyl)adenines VIII were prepared by alkylation of adenine with suitably substituted oxiranes XIII or 2-hydroxyalkyl p-toluenesulfonates IV and VI. After protection of the adenine amino group by benzoylation (compounds IX) or amidine formation (compounds X), the intermediates were alkylated with diisopropyl p-toluenesulfonyloxymethanephosphonate (XI) in the presence of sodium hydride. After deprotection, the obtained phosphonate diesters XII were converted into phosphonic acids I by transsilylation and hydrolysis. This synthetic scheme was used for the preparation of ethyl (Ie), propyl (If), 2-propyl (Ig), 2-methylpropyl (Ih), cyclopropyl (Ii), cyclohexyl (Ij), benzyl (Ik) and phenyl (Il) derivatives. The 2'-trifluoromethyl derivative XXIIa was prepared analogously from 9-(2-hydroxy-3,3,3-trifluoropropyl)adenine (XXa), obtained by alkylation of adenine sodium salt with 2-hydroxy-3,3,3-trifluoropropyl bromide. 2'-Trimethylsilyl derivative XIXa was obtained by alkylation of adenine with 2-diisopropylphosphonomethoxy-3-(4-toluenesulfonyloxy)propyltrimethylsilane (XVII) followed by transsilylation and hydrolysis of diester XVIIIa. 2,6-Diaminopurine derivatives XVIIId and XXIIb were obtained analogously. 9-(3-Phosphonomethoxybutyl)adenine (XXVIII) and 9-(2-methyl-2-phosphonomethoxypropyl)adenine (XXXV) were prepared from the corresponding hydroxy derivatives XXVIb and XXXII, respectively, by the same reaction pathway as derivatives I.