DNA with zwitterionic and negatively charged phosphate modifications: Formation of DNA triplexes, duplexes and cell uptake studies

Two phosphate modifications were introduced into the DNA backbone using Staudinger reaction between 3’,5’-dinucleoside ?-cyanoethyl phosphite triester formed during synthesis and sulfonyl azides, 4-(azidosulfonyl)- N,N,N -trimethylbutan-1-aminium iodide (N+ azide) or p -toluenesulfonyl (tosyl Ts) azide, to provide either a zwitterionic phosphoramidate with N+ modification negatively charged for Ts in sequence. The incorporation of these led formation thermally stable parallel triplexes, regardless number incorporated oligodeoxynucleotides (ONs). For both Ts-modified ONs, antiparallel duplexes complementary RNA more than those (except ONs middle sequence). Additionally, thermal stability that was less dependent on ionic strength native duplexes. thermodynamic analysis melting curves revealed it is reduction unfavourable entropy, despite decrease favourable enthalpy, which responsible stabilisation modification. N+ONs also demonstrated greater resistance nuclease digestion by snake venom phosphodiesterase I corresponding Ts-ONs. Cell uptake studies showed Ts-ONs can enter nucleus mouse fibroblast NIH3T3 cells without any transfection reagent, whereas, remain concentrated vesicles within cytoplasm. These results indicate are promising various vivo applications.