Structural factors affecting affinity of cytotoxic oxathiole-fused chalcones toward tubulin

• New sub-class of chalcones with high cytotoxic activity.
• Chalcone–tubulin two modes of interaction.
• Relationship between chalcone structure, cytotoxicity and interaction with tubulin.
• Bioequivalence of benzoxathiole and 3,4,5-trimethoxyphenyl units.

Synthesis, in vitro cytotoxic activity, and interaction with tubulin of (E)-1-(6-alkoxybenzo[d][1,3]oxathiol-5-yl)-3-phenylprop-2-en-1-one derivatives (2) are described. Some of the compounds demonstrated cytotoxic activity at submicromolar concentrations, and the activity could be related to interaction with tubulin at the colchicine binding site. Interaction of selected derivatives with tubulin was evaluated using molecular modeling, and two different modes of the interaction were identified. The proposed models demonstrate how particular structural fragments participate in binding to the tubulin and explain the importance of the fragments for cytotoxic activity. It was demonstrated that concerning binding to tubulin, the 6-alkoxybenzoxathiole ring can be considered as structural equivalent of trimethoxyphenyl motif of colchicine, podophyllotoxin or combretastatin A4. The observation opened new ways of rational modifications of several groups of tubulin binders.

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