Synthesis Of Pyrazolo[1,5-a]indole Derivatives Benzylidene Triflate And DNA Binding Properties, The Inhibitory Activity Towards DNA Toposiomerase Ι Of The Compounds

It was reported firstly by Hajime Katayama in1997that pyrazolo[1,5-a]indolederivatives have strong cytotoxic activity against cancer cells. Our group gave a newmethod on pyrazolo[1,5-a]indole synthesis by using Cu(I)-catalyzed intramolecularamination reaction to synthesize a series of skeletons and derivatives ofpyrazolo[1,5-a]indole in2007. To further explore the synthetic method and anti-tumormechanism of pyrazolo[1,5-a]indole derivatives, a new synthetic route was designed,and the relationship between compound structures and antitumor activities was revealedby the DNA interaction.In order to introduce diverse substituents to the pyrazolo[1,5-a]indole, in thispaper, we designed the cross-coupling reaction of different benzaldehyde withpyrazolo[1,5-a]indole and its analogs. As a result, we found that when using InCl3aslewis acid, the p-substituent of benzaldehyde connecting directly to disubstituted aminecould give products in high yield. Targeting products were obtained bypyrazolo[1,5-a]indole intermediates reacting with MeI.In this paper, we synthesized eight pyrazolo[1,5-a]indole derivatives (BY1-BY8)through reported routes. And then the inhibitory activities against DNA topoisomerase Ιof these eight compounds were evaluated by agarose-gel electrophoresis experiments.The results manifested that all of these compounds exhibited potent inhibitory activitiesagainst DNA topoisomerase Ι and compound BY4could inhibit the activity oftopoisomerase Ι completely at the concentration of8μM. There was electrostaticinteraction between compounds and DNA after the catalytic activity of topoisomerase Ιwas totally inhibited.To understand the reaction mechanism of the compounds as antineoplastic agent, the interaction of calf thymus DNA (ct-DNA) with the compounds was studiedextensively by various spectroscopic techniques, viscosity measurements and gelelectrophoresis. The results showed that compounds could intercalate into DNA basepairs in different degree and there was electrostatic attraction existed as well. In theseeight pyrazolo[1,5-a]indole derivatives, the compound BY4with naphthalene had theadvantage of appropriate planarity, it was easy to interact with DNA. Compound BY3,BY6and BY8showed high binding capacity due to eletron-withdrawing group. Thestudy was not only helpful to understand the antitumor mechanisms ofpyrazolo[1,5-a]indole derivatives in molecular level, but also provided theoreticalguidance for designing effective anticancer drugs in clinical.