The Zika virus (ZIKV) is believed to cause birth defects,
and no
anti-ZIKV drugs have been approved by medical organizations to date.
Starting from antimicrobial lead compounds with a pyrazolo[3,4-
d
]pyridazine-7-one scaffold, we synthesized 16 derivatives
and screened their ability to interfere with ZIKV infection utilizing
a cell-based phenotypic assay. Of these, five compounds showed significant
inhibition of ZIKV with a selective index value greater than 4.6.
In particular, compound
9b
showed the best anti-ZIKV
activity with a selectivity index of 22.4 (half-maximal effective
concentration = 25.6 μM and 50% cytotoxic concentration = 572.4
μM). Through the brine shrimp lethality bioassay,
9b
,
10b
,
12
,
17a
, and
19a
showed median lethal dose values in a range of 87.2–100.3
μg/mL. Compound
9b
was also targeted to the NS2B-NS3
protease of ZIKV using molecular docking protocols, in which it acted
as a noncompetitive inhibitor and strongly bound to five key amino
acids (His51, Asp75, Ser135, Ala132, Tyr161). Utilizing the pharmacophore
model of
9b
, the top 20 hits were identified as prospective
inhibitors of NS2B-NS3 protease, and six of them were confirmed for
their stability with the protease via redocking and molecular dynamics
simulations.