Stabilization and improvement of a promising influenza antiviral: Making a PAIN PAINless

The viral envelope protein hemagglutinin (HA) plays a critical role in influenza entry and thus is an attractive target for novel therapeutics. The small molecule tert-butylhydroquinone (TBHQ) has previously been shown to bind to HA and inhibit HA-mediated entry with low micromolar potency. However, enthusiasm for the use of TBHQ has diminished due to the compound's antioxidant properties. In this work we show that the antioxidant properties of TBHQ are not responsible for the inhibition of HA-mediated entry. In addition, we have performed a structure-activity relationship (SAR) analysis of TBHQ derivatives. We find that the most promising compound, 3-Tert-butyl-4-methoxyphenol, exhibits enhanced potency (IC50 = 0.6 μM), decreased toxicity (CC50 = 340 μM), and increased stability (t1/2 < 48 h). Finally, we have characterized the binding properties of 3-Tert-butyl-4-methoxyphenol using NMR and molecular dynamics to guide future efforts for chemical optimization.