Synthesis of 3'-DMTBS-5'-O-(4,4') tetrahydrofuran-2-yl)-6-oxo-6,9-dihydro-1H-purin-2-yl)isobutyramide from tert-butyldimethylchlorosilane and N-(9-((2R,3R,4S,5R)-3,4-dihydroxy-5-(1-hydroxy-2,2-bis(4-methoxyphenyl)-2-phenylethyl)-6-oxo-6,9-dihydro-1H-purin-2-yl)isobutyramide. -dimethoxytrityl)-N2-isobutyryl acylcytidine in the following general steps: to a solution of compound HLH (23.9 g, 36.450 mmol, 1.00 eq.) in N,N-dimethylformamide (120 mL) was added tert-butyldimethylchlorosilane (8.24 g, 54.675 mmol, 1.50 eq.) and 1H-imidazole ( 6.204 g, 91.124 mmol, 2.50 equiv). The reaction mixture was stirred at 25 °C overnight. After completion of the reaction, the reaction was quenched with methanol (5 mL) and the mixture was concentrated to give the residue. The residue was purified by preparative HPLC (mobile phase: water (containing 0.225% formic acid)-acetonitrile gradient elution) to afford compound LII (6.7 g, 24% yield) as a yellow solid.LC-MS analysis showed ESI-MS m/z 770.3 [M+H]+.
