Synthesis of Specifically Modified Oligonucleotides for Application in Structural and Functional Analysis of RNA

Figure 4

Synthesis of the guanosine-phosphoramidite. (i) 8-bromoguanosine 15, 2.0 eq. L3, 0.1 eq. Pd(PPh₃)₄, 0.2 eq. CuI, 1.2 eq. DIPEA, 40°C, 20 h (80%); (ii) 16, pyridine, 8.2 eq. TMS-Cl, 0°C, 2 h, 2.2 eq. isobutyric anhydride, rt, 2 h, NH₃ up to 2.5 M, 0°C; (iii) 17, pyridine,1.5 eq. DMT-Cl, 0°C, 2.5 h; (iv) 18, THF, 3.7 eq. pyridine,  1.5 eq. AgNO₃, 15 min, 1.7 eq. TBDMS-Cl, rt, 8.5 h; (v) 19, DCM, 4 eq. DIPEA, 1.5 eq. 2-cyanoethyl-N,N-diisopropylchlorophosphoramidite, rt, 2.5 h.