-fluoro-5-ethyluridine (49) were found to possess significant anti-HBV activity against DHBV in primary duck hepatocytes with
EC(50) values of 4.1, 3.3, 40.6, 3.8, 0.2, and 39.0 μM, respectively. Compounds 23, 25, 39, 48, and 49 (EC(50) = 41.3, 33.7, 19.2, 2.0-4.1, and 39.0 μM, respectively) exhibited significant activity against wild-type human HBV in 2.2.15 cells.