Studies On The Synthesis, Properties And Biological Activities Of Isonucleosides And Their Incorporated Oligonucleotides

In the search for effective, selective and nontoxic anticancerand antiviral agents, the discovery of new class of nucleosides isof immense importance. Isonucleoside is a new class of nucleosideanalogues in which the nucleobase is linked to a position of riboseother than C-1'. Therefore isonucleosides have attracted muchattention owing to their chemical and enzymatic stability andpotential antiviral activities. In order to avoid lengthy synthetic routes, we synthesizedisonucleosides by using an epoxide opening by a nucleobase itselfin the basic conditions. The key intermediates 2,5:3,4-dianhydro-L-talofuranose dimethylacetal 18 was synthesized from D-glucosein 7 steps. Compound 18 reacted with nucleobases (adenine, uracil,thymine, guanine, cytosine and 5-fluorouracil) in DMF, aregio-selective epoxide opening took place in the presence ofpotassium carbonate and a crown ether at 80-100°C to give aseries of 4-deoxy-4-nucleobase-2,5-anhydro-L-mannitols 36-39,42, 43, 45. Compound 45 was obtained in the form of a5-fluorouracil combined with two tetrahydrofuran rings. There are two active centers, the epoxide and tosyl group, in6-O-p-tosyl-2,5:3,4-dianhydro-L-talofuranose dimethyl acetal 19which can be substituted by nucleophilic reagents. The pyrimidinebases prefer to attack the tosyl group under the same conditions as18. Surprisingly, when adenine was used instead of pyrimidineunder the same conditions, two new compounds, 4-deoxy-4-adenyl-2,5:3,6-dianhydro-L-mannofuranose dimethyl acetal 31 and4-(S)-adenyl-5-(R)-[1'-(R)-hydroxy-2',2'-dimethoxy] ethyl-2,3-dihydrofuran 30, which is formed by reformation result oftetrahydrofuran ring, were obtained.Thymine reacted with 6-O-benzyl-2,5:3,4-dianhydro-L-talo-furanose dimethyl acetal 21 to give a interest structure whichinvolve one nucleobase and two tetrahydrofuran ring 49.Compound 50 and 53 were used to synthesize analoques ofisoddA 52 and 55. The Syn conformation of 52 was determined byNOESY.Computer dynamic minimized conformation and biologicalactivities of isonucleosides were studied. The biological resultsshowed that several compounds posses weak antitumor activity.By using the standard Applied Biosystem cycle (1.0 μ moland 10 μ mol scale) on DNA synthesizer, nine oligomers(eight 14mer, one 7 mer) were synthesized. Two isothymidines wereincorporated in different position of single strand. Purification ofthe oligomers were performed by HPLC and were desalted on aSephadex 15 column. Four of the nine oligomers were identifiedby matrix assisted laser desposition mass spectrometry. One of thenine oligomers was tested against snake venomphosphodiesterase(SVPDE), the result indicated that it wasn't thesubstrate of the 3'-exonuclease. The hybridization of the aboveoligomer with dA14 were determined by UV melting point (Tm)measurment, only the oligomer consisting by L-isonucleoside canhybride with normal oligodeoxynucleotide to give Tm. The resultswere discussed.