Compound IV showed the highest activity with approximately
twofold higher activity than compound II. Both compounds slightly
differ only by adjacent position of hydroxyl groups with respect to
each other. Hydroxyl group at position R2 showed similar binding
mode as observed in case of compound II, where the hydroxyl
group was attached at an adjacent R3 position. Hydroxyl group at
R2 position in compound IV revealed simultaneous hydrogen bonding
interactions with Arg 209 and Asn 205 at a distance of 3.339 Å
and 2.566 Å, respectively (Figs. 3 and 4). The distinctive feature of
compound IV was the third hydrogen bonding interaction between
the carbonyl moiety of N-t-butyl side chain and His 60 (at a distance
of 3.339 Å), which could be a major reason for its highest
activity among all compounds lacking this molecular interaction.
The same carbonyl moiety also made a favorable electrostatic contact
with positively Cu atom. Other two compounds also showed
potent, but relatively lower activity than compound II and IV.
Experimental and computational insights revealed the fact that
position R2 should be targeted for further optimizing the compound
to generate better lead compounds against tyrosinase
enzyme