(1R,3R,4R,7S)-1-((Bis(4-methoxyphenyl)(phenyl)methoxy)methyl)-3-(2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)-2,5-dioxabicyclo[2.2.1]heptan-7-yl (2-cyanoethyl) diisopropylphosphoramidite