Synthesis and structure-activity relationships of 6-substituted 2',3'-dideoxypurine nucleosides as potential...

In order to study the structure-activity relationships of 2',3'-dideoxypurine nucleosides as potential anti-HIV agents, various 6-substituted purine analogues have been synthesized and examined in virus-infected and uninfected human peripheral blood mononuclear cells. N6-methyl-2',3'-dideoxyadenosine (D2MeA, 7a) was initially synthesized from adenosine via 2',3'-O-bisxanthate 3. As extension of this reaction to other N6-substituted compounds failed, a total synthetic method utilizing 2',3'-dideoxyribose derivative 9 was used for the synthesis of other purine nucleosides. An acid-stable derivative of N6-methyl-2',3'-dideoxyadenosine, 2'-fluoroarabinofuranosyl analogue 32 (D2MeFA), has been synthesized from the appropriate carbohydrate 24 by condensation with N6-methyladenine 23. Among these compounds, N6-methyl derivative (D2MeA) 7a proved to be one of the most potent antiviral agents. The order of potency for the 6-substituted compounds was NHMe greater than NH2 greater than Cl approximately N(Me)2 greater than SMe greater than OH approximately NHEt greater than SH greater than NHBn approximately H. The results suggest that a bulk tolerance effect at the 6-position of the 2',3'-dideoxypurine nucleoside may dictate the antiviral activity of these compounds. Acid-stable analogue 32 (D2MeFA) was found to be 20-fold less potent than the parent compound. Both D2MeA and D2MeFA were resistant to calf intestine adenosine deaminase. The presence of a fluorine atom in the carbohydrate moiety greatly increased stability to acid, making D2MeFA a potential orally active antiviral agent that could be useful for the treatment of retroviral infections in humans.