F-19 NMR OF RNA - THE STRUCTURAL AND CHEMICAL ASPECTS OF 5-FLUORO-CYTIDINE AND 5-FLUORO-URIDINE LABELING OF OLIGORIBONUCLEOTIDES

Results of PM3 semiempirical calculation revealed that energy and hydr ogen bonds geometry of 1-methyl-5-fluoro-uracil and -cytosine base-pai rs with 9-methyladenine and -guanine respectively are virtually the sa me as for the natural bases. Analysis of proton coupling constants pro ved that the sugar puckering of 5-fluorouridine and 5-fluorocytidine i s analogous to non-modified ribonucleosides. 5-Fluorocytidine was regi oselectively introduced to oligoribonucleotides, prepared using 2'-O-t ert-dimethylsilyl protection, via post-synthetic quantitative ammonoly sis of 4-O-methyl-5-fluorouridine derived precursor.