Synthesis And Activities Of Selective Ligands For Dimeric G-q?adruplex DNA

G-quadruplex is a special secondary structure of nucleic acid which consists of G-rich sequences.It plays an important role in gene transcription,replication,translation regulation,chromosome maintenance and reorganization.There are many G-rich sequences in different regions of hunan genome and most of them can fold into monomeric G-quadruplexes.However,it is reported that only telomeric DNA and r(GGGGCC)n RNA repetitions can form multimeric G-quardruplexes in human genome in recent years.Therefore,developing ligands to seclectively recognize and bind to multimeric G-quadruplexes is meaningful for studying the structures and function of G-quardruplex and even for designing bioluminescent probes or drug molecules targeting G-quardruplexes.In this paper,we designed two different kinds of dimeric G-quadruplex binders and investigated their specific interaction with dimeric G-quadruplexes.In the first part of the work,a phenanthroimidazole ethylenediame Pt(II)complex with coumarin group(PtL)was synthesized and fully characterized on the basis of MS(LR and HR),1H-NMR,IR and elemental analysis.Complex PtL showed higher affinity,selectivity and thermal stabilization(?Tm=16.2?)for mixed-type dimeric G-quadruplex(G2T1)over monomeric G-quadruplex(G1)and duplex DNA by means of CD spectroscopy,CD-melting,gel electrophoresis and UV-Vis titration.Based on the results obtained from UV-Vis titrations and spectrofluorimetric titrations with Ap-labelled G2T1,we deduced that the possible binding mode between complex PtL and G2T1 was end-stacking and external-binding.In the second part of the work,we designed three berberine dimers(la-c)with polyether linkers of varying lengths.Their binding affinities,selectivities and thermal stabilization to human telomere dimeric G-quadruplexes had been determined by UV-Vis titrations,fluorescence spectroscopy,CD spectroscopy,CD-melting and electrophoresis.These studies showed that compound la with the shortest polyether linker displayed the highest affinity(Ka>108M-1)and 76-508-fold higher selectivity for mixed-type G2T1 over anti-parallel G2T1 and three human telomeric monomeric G-quadruplexes,G1 c-kit 1 and c-kit 2.Compounds la-c induced the formation of antiparallel quadruplexes and compound la showed a higher stabilization for mixed G2T1 than for anti-parallel G2T1,G1 and duplex ds 26.Spectroscopic studies suggest that compound la could bind to mixed-type G2T1 via end-stacking and external binding modes.These results suggest that the polyether linkers in these compounds play an important role in regulating the binding affinity and selectivity towards mixed-type G2T1.MTT assay showed that this kind of compounds la-c had low cytotoxicities and suitable to be used as dimeric G-quadruplex bioprobes.In conclusion,we have synthesized two kinds of excellent ligands selectively interacting with mixed-type dimeric G-quadruplex.These results may provide useful guidance for the rational design of selective dimeric G-quadruplex binders,bioprobes and some potential drug molecules targeting dimeric G-quadruplexes.