aValues are the mean of three independent experiments. The MTase activity was measured using a filter binding assay. Assays were carried out in reaction mixture [40 mM Tris-HCl (pH 8.0), 1 mM DTT, 1 mM MgCl2, 2 μM SAM and 0.1 μM 3H-SAM] in the presence of 0.7 μM GpppAC4 synthetic RNA and incubated at 30 °C. SARS-CoV nsp14 (50 nM), vaccinia virus capping enzyme (D1-D12) (41 U), human RNA N7 MTase (hRNMT) (50 nM). Compounds were previously dissolved in 100% DMSO. n.i: no inhibition detected at 50 μM.