The degree of inhibition of multiplication of influenza B virus, Lee strain, in membrane cultures in vitro appears to be directly related to the concentration of the inhibitory compounds used in this investigation. With each of the alkyl derivatives of benzimidazole, evidence for such a relationship was obtained in the range between 60 and 90 per cent inhibition of virus multiplication.
Alteration of the structure of benzimidazole by substitution of alkyl radicals at various positions in either the benzene or the imidazole ring resulted in diverse differences in the capacity to inhibit influenza virus multiplication in vitro. Minor increases in inhibitory activity resulted when one to three methyl groups were introduced at certain positions in the molecule. Marked increases in inhibitory activity were achieved by more extensive substitution in either the benzene or the imidazole ring. The position and nature of substituent groups appeared to be of decisive importance.
Among the more highly active compounds were 2,4,5,6,7-pentamethyl-benzimidazole, 5,6-diethylbenzimidazole, and 2-ethyl-5-methylbenzimidazole. Further extension of the alkyl chain at position 2 caused no significant change in the inhibitory activity of the derivative. The most active compounds studied caused 75 per cent inhibition of Lee virus multiplication in membrane cultures in vitro at concentrations of approximately 0.0002 M. Some of the implications of these findings are discussed.