Solvent-free synthesis, DNA-topoisomerase II activity and molecular docking study of new asymmetrically N,N'-substituted ureas

Abstract

A new series of asymmetrically N,N'-substituted ureas 20–25 was prepared using solvent free conditions, which is an eco-friendly methodology, starting with Schiff bases derived from cinnamaldehyde and p-substituted anilines, which are subsequently submitted to reduction reactions that afford the corresponding asymmetric secondary amines. All of the intermediates were prepared using solvent free reactions, which were compared to traditional methodologies. All of the reactions required a remarkably short amount of time and provided good yields when solvent free conditions were employed compared to other methodologies. The DNA-topoisomerase II-α (topo II-α) activity was evaluated in relaxation assays, which showed that all of the compounds inhibited the enzyme activity at 10 μM, except for urea 24. Furthermore, a molecular docking study indicated that the compounds 20–25 binding to the topo II-α are able to interact with the same binding site as the anticancer drug etoposide, suggesting that the ureas could inhibit the enzyme by the same mechanism of action observed for etoposide, which prevents re-ligation of the DNA strands.

Scheme 1

Synthesis of asymmetrically N,N'-substituted ureas.

Figure 1

Effect of ureas on topo II-α Line 1: Etoposide (100 μM) + pBR322; line 2: pBR322 only; line 3: pBR322 + topo II-α; line 4: pBR322 + topo II-α + 23 (10 μM); line 5: pBR322 + topo II-α + 24 (10 μM); line 6: pBR322 + topo II-α + 21 (10 μM); line 7: pBR322 + topo II-α + 22 (10 μM); line 8: pBR322 + topo II-α + 20 (10 μM); line 9: pBR322 + topo II-α + 25 (10 μM).

Figure 2

superposition of experimentally observed etoposide (carbon atoms in yellow) interactions and compound 22 (carbon atoms in cyan) docking interactions into the DNA (carbon atoms in green) binding site of topo II-α (carbon atoms in white); H atoms were removed to improve clarity (figure generated with PyMOL software).