Antirhino/Enteroviral Vinylacetylene Benzimidazoles:  A Study of Their Activity and Oral Plasma Levels in Mice

In an effort to find an orally bioavailable antiviral for the treatment of rhino/enteroviral infections, a series of vinylacetylene benzimidazoles (11a−o, 12, and 18a) was made. Initial studies of this class of antivirals showed that fluorine substitution on the left-hand phenyl ring in combination with the vinylacetylene moiety gave the requisite mix of physical properties to achieve good in vitro antiviral activity as well as respectable oral bioavailability in rhesus monkeys. To ascertain the generality of this finding and to broaden the scope of the structure−activity relationship (SAR), the present study concentrated on fluoro substitution of this class of molecules. The initial antiviral activity for each analogue was measured using human rhinovirus 14 (HRV-14). This served as an indicator of general antiviral activity for SAR purposes. Subsequently, the spectrum of antirhino/enteroviral activity of the more interesting analogues was evaluated through testing against a panel of seven additional rhino/enteroviruses. Broad-spectrum activity was present and consistent for all analogues tested, and it tracked closely with the antiviral activity observed against HRV-14. A simple screening protocol for oral bioavailability was established whereby compounds were administered orally to mice and plasma levels were measured. This procedure facilitated the evaluation of numerous analogues in a rapid manner. The C max was used as a measure of oral bioavailability to allow relative ranking of compounds. In general, fluorine substitution directly on the left-hand aromatic ring does give good oral blood levels. However, fluorine incorporation at other positions in the molecule was not as effective at maintaining either the activity or the oral plasma levels. The constructive combination of activity and oral plasma levels was maximized in three derivatives: 11a,e,g.