Molecular mechanisms behind higher activities of the test compounds
compared with standard compound (Kojic acid) were
probed using molecular docking and scoring. In case of compound
II, hydroxyl group made a favorable hydrophilic contact with Arg
209 through hydrogen bonding at a distance of 3.222 Å (Fig. 3).
Interestingly, the same hydroxyl group was found to be simultaneously
connected with Asn 205 via hydrogen bonding at a distance
of 2.641 Å (Fig. 4). Such dual binding behavior of hydroxyl
group at R1 position could be one of the major reason behind comparatively
higher inhibitory effect of compound II than compound I
and III. In addition to hydrogen bonding, favorable electrostatic
interaction was observed between amide group of N-t-butyl side
chain of compound II and Cu atom. Carbonyl moiety of the N-tbutyl
side chain also played a positive role in favorable electrostatic
interactions with His 208. No considerable electrostatic clash
was observed in macromolecular complex of compound II with
amino acid residues of tyrosinase