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The antiviral activity of homoisoflavonoids, a class of flavonoids, was determined in vitro against a large panel of enteroviruses. The inhibition of viral replication was monitored on BGM (Buffalo Green Monkey) cells, and the concentration required for 50% inhibition (IC50), as well as the selectivity index (SI) were determined. None of the substances were effective against Sabin type 1 poliovirus (PV1), but most of them showed a low cytotoxicity and a marked antiviral activity against Coxsackie virus B1, B3, B4, A9 and echovirus 30.

Synthetic flavans, isoflavans and isoflavenes substituted with chloro, cyano and amidino groups were tested for their in vitro activity against poliovirus type 2, Coxsackie virus B4, echovirus type 6 and enterovirus 71. Plaque-reduction assays showed that substituted 3-(2H)-isoflavenes, carrying a double bond in the oxygenated ring, possess antiviral activity higher than that of the corresponding isoflavans. The most effective compounds were 4'-chloro-6-cyanoflavan and 6-chloro-4'-cyanoflavan. Studies on the mechanism of action of these two compounds suggested an effect on the early stages of viral replication.

In this study we investigated the activity of halogeno-, cyano- and amidino-isoflavenes, isoflavans and flavans on the multiplication of human astroviruses. These are naked small round viruses which have been recognized as causative agents of human gastroenteritis, and whose capsid proteins are similar to those of picornaviruses. Although all drugs tested caused a dose-dependent reduction of viral antigen synthesis as monitored by immunofluorescence, the chloro derivatives were the most effective.