6-Chloro-1-[5-deoxy-5-[[(diethoxyphosphinyl)methyl]sulfonyl]-2,3-O-(1-methylethylidene)-β-D-ribofuranosyl]-4-[[(1S)-1-(4-fluorophenyl)ethyl]amino]-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile