Synthesis and properties of 2'-deoxy-8,2'-methylene-cyclopurine nucleosides

A method was developed to synthesize 2'-deoxy-8,2'-methylene-cycloadenosine (1) and -cycloguanosine (2) which were new carbon-bridged cyclopurine nucleosides fixed in a high-anti torsional angle region. 3',5'-Di-O-acetyl-8-methanesulfonyl-2'-O-p-toluene-sulfonyladenosine+ ++ (3) or 2-acetamido-9- (3,5-di-O-acetyl-2-O-p-toluenesulfonyl-beta-D-ribofuranosyl)-6- ethoxy-8-methanesulfonyl-purine (9) was treated with sodium salt of ethyl malonate to give the cyclized nucleosides (4 and 10) in good yields, respectively. Subsequent decarboxylation and deblocking of 4 and 10 afforded 1 and 2 in crystalline form, respectively.