Synthesis of 2',3'-dideoxyisoguanosine from guanosine

2,3'-Dideoxyisoguanosine was synthesized from guanosine via intermediate 6-[(4-methylphenyl)thio]-2-oxo-9-(2',3',5'-tri-O-acetyl-beta-D-ribofuran osyl)-2,3-dihydropurine (4). The 2-oxo, 6-amino and 5'-hydroxy triprotected isoguanosine derivative was utilized to reduce high polarity and promote poor solubility of intermediates. The protecting groups for oxo and 6-amino were easily removed in reduction of olefin in ribose without additional reaction steps. 2',3'-Vicinal diol in ribose sugar moiety was transformed to olefin with Bu3SnH by radical reaction via bisxanthate. Removing 5'-O-TBDMS protecting group gave final product, 2',3'-dideoxyisoguanosine (12) in a 10% overall yield.