Inhibition of Dengue Virus Protease by Eugeniin, Isobiflorin, and Biflorin Isolated from the Flower Buds of Syzygium aromaticum (Cloves)

Dengue virus (DENV) infections are rampant in tropical and subtropical regions of the world with millions of people at risk. There is still no specific antiviral treatment available against these infections. Amongst the different potential therapeutic targets, DENV protease is considered an important target because of its crucial role in the viral replication cycle. We are reporting here a potent DENV protease inhibitor, eugeniin (3), which has been isolated from cloves, along with two other weaker inhibitors, isobiflorin (1) and biflorin (2). In this study, the IC50 values of 3 against the proteases of DENV serotype-2 and -3 were found to be 94.7 nM and 7.5 mu M, respectively. Mechanistically, the compounds 1-3 exhibited a competitive type of inhibition, which were further substantiated by computational docking and saturation transfer difference (STD) NMR spectroscopy. Atomic-level details of the binding of these molecules at the active site of the protease suggested extensive interactions mediated by a network of hydrogen bonds and hydrophobic contacts. With further evaluation, these inhibitors are highly promising in the context of antiviral therapeutics development against DENV.