Synthesis And Biological Activity Of Squaramido-tethered Bisbenzimidazoles As Synthetic Anion Transporters

The exchange of substances and the dynamic anion balance between inside and outside cells are the prerequisites for maintaining their normal morphology and exerting physiological functions.Artificially synthesized small-molecule organic compounds with anion transport activity can promote the transmembrane transport of anions and disrupt the dynamic anion balance,which may cause the change of p H within lysosomes,reduce the activity of lysosomal enzymes,disturb autophagy and eventually lead to cell death.Therefore,such compounds may find high potential applications in the development of a novel class of anti-tumor drugs.So far,many different structural types of anion transporters have been reported,including sulfonamides,ureas,thioureas,pyrroles,imidazoles,indoles,squaramides and benzimidazoles.These small-molecule compounds have good anion transport activity,and notably some of them also show strong anti-tumor activity.Because of its good biocompatibility and ability to bind anions through hydrogen bonds,benzimidazole is a good structural unit for building anion transporters.Introduction of benzimidazolyl unit into the structural skeletons of anion transporters can enhance their anion binding ability and anion transport activity.On the other hand,squaramide has a conjugated four-membered ring structure.Compared with ureas,the squaramido N-H unit is more acidic and may form stronger hydrogen bonding.In this thesis,squaramide and benzimidazole were used as building blocks to design and synthesize 14 squaramido-tethered bisbenzimidazoles,and their structures were confirmed by NMR(¹H,¹³C)and ESI-MS（LR,HR）.ESI-MS and ¹H NMR titration experiments show that all the 14 compounds can bind chloride anions in a 1:1 manner.Compounds 1-13 containing two benzimidazolyl subunits have a stronger ability to bind chloride anions than compound 14 containing only one benzimidazolyl subunit.Chloride ion selective electrode experiments suggest that compounds 1-13 exhibit moderate chloride ions transport activity,and the activity may be regulated by the substituents on the benzimidazolyl subunits.The anion and cation selectivity experiments and U-tube experiments indicate that the compounds 1-13may exert the anion transmembrane transport activity most probably via an anion exchange process.Chloride ion selective electrodes experiments under condition of different p Hs show that compounds 1-13 exhibit higher ion transport activity at acidic p H than at physiological p H.MTT experiment shows that these compounds have moderate anti-tumor activity,and flow cytometry experiments show that these conjugates exhibit modest cytotoxicity probably in an apoptotic fashion.In summary,in this study,squaramido-tethered bisbenzimidazoles were designed and synthesized,and their anion binding ability,anion transmembrane transport activity and antitumor activity were studied.The experimental results show that compounds1-13 can bind chloride ions strongly and may exert the anion transmembrane transport activity most probably via an anion exchange process.At the same time,compounds1-13 exhibit moderate p H-dependent chloride ion transport activity and anti-tumor proliferation activity.These findings are expected to provide some useful guidance for the rational design of novel small-molecule anti-tumor drugs.