Effect of adenosine on the supramolecular architecture and activity of 5-fluorouracil

The reactions of adenosine (Ad) with 5-halouracils (5XU where X = F for 1, Cl for 2, Br for 3 and I for 4) resulted in the formation of co-crystals 1-4 in monoclinic with P2(1) space group. Despite of great variation in the halo substituent at the 5th position of the uracil, each structure contains the same number and same type of non-covalent interactions i.e., primary N-H center dot center dot center dot N, N-H center dot center dot center dot O, O-H center dot center dot center dot N, O-H center dot center dot center dot O hydrogen bonds and secondary C-H center dot center dot center dot O and X center dot center dot center dot O interactions within these motifs as well as with neighboring molecules. As compared to Ad the size of cavity increases in co-crystal 1 to accommodate the 5FU as a guest. With the variation of halogen from fluoro to iodo on the uracil, the orientation of the molecules remains the same with a slight difference in the dihedral angle in all the co-crystals 1-4. This study demonstrates that hydrogen-bonded interactions between adenosine and halouracils provide a supramolecular assembly to these co-crystals. Computational studies illustrate that the size of the halo substituents on uracil has no effect on the hydrogen bond interaction energy. It further reveals that the orientation of molecules remain same in both solid phase as well as in the gaseous phase. The antitumor and DNA cleavage activity studies show that the antitumor activity of 5-fluorouracil against MCF-7 breast cancer decreases in the presence of adenosine. (C) 2012 Elsevier B.V. All rights reserved.