shown to inhibit Sindbis virus, with IC50 values of 0.5, 1.9, and 6.1 μM, respectively. The latter three compounds also had significant synergistic effects against SFV when combined with 3′-amino-3′-deoxyadenosine. In contrast to previous work on other viruses, the antiviral activity of 13 was mapped to take place in virus replication phase. The efficacy was also shown to be independent of external