SYNTHESIS OF 1'NUMBER,2',3',4'NUMBER,5',5''-(H-2)6-BETA-D-RIBONUCLEOSIDES AND 1'NUMBER,2',2'',3',4'NUMBER,5',5''-(H-2)7-BETA-D-2'-DEOXYRIBONUCLEOSIDES FOR SELECTIVE SUPPRESSION OF PROTON RESONANCES IN PARTIALLY-DEUTERATED OLIGO-DNA, OLIGO-RNA AND IN 2,5A CORE (H-1-NMR WINDOW)

Raney nickel-(H2O)-H-2 exchange reaction on an epimeric mixture of methyl alpha/beta-D-ribofuranoside [alpha/beta = approximately 3:10]1 produced methyl 1#,2,3,4#,5,5'-H-2(6)-alpha/beta-D-ribofuranoside 2 [> 97 atom % H-2 at C2, C3, C5/5'; approximately 85 atom % H-2 at C4 (C4'#); approximately 20 atom % H-2 at C1(C1'#)] which was obtained in 60 - 80 % yield along with epimeric xylo and arabino by-products. Toluoylation of the crude 2 in dry pyridine and a careful separation on a column of silica gel gave pure 1-O-methyl-2,3,5-tri-O-(4-toluoyl)-alpha/beta-D-1#,2,3,4#,5,5'-H-2(6)-ribofuranoside 4 (48 %). Conversion of 4 to 1-O-acetyl-2,3,5-tri-O-toluoyl-alpha/beta-D-1#,2,3,4#,5,5'-H-2(6)-ribofuranoside 6 (82 %) provided the crucial building block for the synthesis of deuterionucleosides for RNA or DNA synthesis. Compound 6 was then condensed with silylated uracil, N4-benzoylcytosine, N6-benzoyladenine, N2-acetyl-O6-diphenylcarbamoylguanine and thymine in anhydrous solvent using trimethylsilyl trifluoromethanesulfonate to give the corresponding isomerically pure 1'#,2',3',4'#,5',5"-H-2(6)-ribonucleoside derivatives 7, 8, 9, 10, 11 in 75, 85, 60, 73 and 91 % yields, respectively. 1'#,2',3',4'#,5',5"-H-2(6)-ribonucleosides 13 - 16 were converted in high yields to the corresponding 1'#,2',2",3',4'#,5',5"-H-2(7)-2'-deoxynucleosides 41 - 44 in the following manner: 3',5'-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl (TPDS))-1'#,2',3',4#',5',5"-H-2(6)-nucleosides 29 - 32 were converted to the corresponding 2'-O-phenoxythiocarbonyl derivatives 33 - 36, which were deoxygenated by tri-n-butyltin deuteride to give 1'#,2',2",3',4'#,5',5"-H-2(7)-2'-deoxynucleosides 37 - 40 and subsequently deprotected to give 41 - 44. Pure 1'#,2',3',4'#,5',5"-H-2(6)-ribonucleoside derivatives 12 - 15, 1'#,2',2",3',4'#,5',5"-H-2(7)-2'-deoxynucleoside blocks 41 - 44 and their natural-abundance counterparts were then used to assemble partially deuterated ribonucleotide-dimers (* indicates deuterated moiety): UpA* 77, CpG* 78, ApU* 79, GpC* 80, partially deuterated 2'-deoxyribonucleotide-dimers d(TpA*) 93, d(CpG*) 94, d(ApT*) 95, d(GpC*) 96 and partially deuterated 2,5A core (A*2'p5'A2'p5'A*) (109). These nine partially deuterated oligonucleotides were subsequently compared with their corresponding natural-abundance counterparts by 500 MHz H-1-NMR spectroscopy to evaluate the actual NMR simplifications achieved in the non-deuterated part (H-1-NMR window) as a result of specific deuterium incorporation. Detailed 1D H-1-NMR (500 MHz), 2D correlation spectra (DQF-COSY & TOCSY), T1 measurements for H-1-, C-13- and INEPT C-13-NMR spectra have been presented and discussed to assess the utility of stereospecific deuterium incorporation to create the H-1- or C-13- NMR window.