Scheme 1. Synthesis of fluorene-labeled 2′-deoxycytidine and 2′-deoxycytidine 5′-O-triphosphate derivatives. Reagents and conditions: (i) CH3I, t-BuOK, THF 0 °C → rt overnight, 83%; (ii) TFA, CH2Cl2 0 °C → rt, 1–3 h; (iii) Ac2O, THF rt, 1 h, 96% over 2 steps; (iv) AcBr, AlCl3, CH2Cl2 reflux, 4 h, 84%; (v) NaOH, MeOH–H2O, 80 °C, 60 h, 81%; (vi) propargyl bromide, K2CO3, CH3CN 70 °C, 24 h, 82%; (vii) 8, PdCl2(PPh3)2, CuI, NEt3, DMF 45 °C, 3 h, 85%; (viii) POCl3, PO(OCH3)3, 0 °C, 4 h: (ix) (n-Bu3NH)2H2P2O7, NBu3, DMF, 0 °C, 1 h; (x) 1 M TEAB, 16% from 9.
