1, 2, and 3: Base = adenine, 4: Base = N4-Bz-cytosine, 5 and 6: Base = cytosine. [Note: Before tosylation, dC was converted to N4-Bz-deoxycytidine 7 with benzoic anhydride, DIEA in pyridine, microwave irradiation (2 min – 300 W). Prior to the enzymatic phosphorylation, the N4-protected dCDP analogue 8 obtained directly from 4 was debenzoylated to 5 using methanolic ammonia.]