When skeletons of Win compounds were used as templates, computer-assisted drug design led to the identification of a novel series of imidazolidinone derivatives with significant antiviral activity against enterovirus 71 (EV 71), the infection of which had resulted in about 80 fatalities during the 1998 epidemic outbreak in Taiwan. In addition to inhibiting all the genotypes (A, B, and C) of EV 71 in the submicromolar to low micromolar range, compounds 1 and 8 were extensively evaluated against a variety of viruses, showing potent activity against coxsackievirus A9 (IC(50) = 0.47-0.55 microM) and coxsackievirus A24 (IC(50) = 0.47-0.55 microM) as well as moderate activity against enterovirus 68 (IC(50) = 2.13 microM) and echovirus 9 (IC(50) = 2.6 microM). Our SAR studies revealed that imidazolidinone analogues with an aryl substituent at the para position of the phenoxyl ring, such as compounds 20, 21, 27, 57, 58, and 61, in general exhibited the highest activity against EV 71. Among them, compound 20 and its corresponding hydrochloride salt 57, in terms of potency and selectivity index, appear to be the most promising candidates in this series for further development of anti-EV-71 agents. Preliminary results of the study on the mode of action by a time-course experiment suggest that test compounds 1 and 8 can effectively inhibit the virus replication at the early stages, referring to virus attachment or uncoating. This indicates that the surface protein may be the target for this type of compounds.