A general synthesis of water soluble upper rim calix[n]arene guanidinium derivatives which bind to plasmid DNA

The reaction of O-alkylated p-aminocalixn]arenes (n=4, 6, 8) with N,N′-di(tert-butoxycarbonyl)thiourea in the presence of HgCl₂ and subsequent removal of the protective groups with hydrochloric acid led to the new water soluble calixn]guanidinium derivatives (p-guanidiniumcalixn]arenes) 20-23. With the exception of tetraoctyl-p-guanidiniumcalix4]arene 21, which forms a macroscopic gelatinous aggregate even at very low concentration, all the synthesised guanidinium calixarenes show good solubility in water and sharp NMR signals. Moreover, these compounds are not cytotoxic and bind to plasmid DNA.