Fig. 3

Colchicine binding conformation (A) and proposed binding for compounds 3d (B), 3f (C), 3h (D) and 3l (E) in the colchicine site. All the derivatives presented the trimethoxyphenyl ring in proximity to βCys241, while the substituted phenyl group at position 2 of the central core was sited at the interface between the two tubulin subunits, pointing toward a loop in the α-subunit (αSer178-αThr179). Compound 3d presented two main interactions with βCys241, different anchoring contacts with the surrounding residues and no clashes with the tubulin structure. The rest of the compounds, even if conserving different interactions, including the important interaction with βCys241, presented different clashes with the surrounding residues, suggesting a non-optimal occupation of the colchicine site and indicating a reduced affinity for tubulin. The carbon atoms of the tubulin α unit residues are shown in lilac, while the carbon atoms of the β unit residues are represented in teal. Hydrogen bonds are shown as orange dashed lines, hydrophobic interactions as green dashed lines and distance clashes as red dashed lines.