RNA MODIFIED URIDINES .7. CHEMICAL SYNTHESIS AND INITIAL ANALYSIS OF TRANSFER-RNA D-LOOP OLIGOMERS WITH TANDEM MODIFIED URIDINES

The first chemical synthesis of oligoribonucleotides with adjacent and significantly different modified uridines, the hydrophobic dihydrouri dine, D, and the hydrophilic 3-[3-(S)-amino-3-carboxypropyl]-uridine, (acp)U-3, is reported. The trimers Dp-acp(3)UpA, Up-acp(3)UpA, DpUpA a nd UpUpA, and the dimer Dp-acp(3)U were synthesized and initial struct ural analysis performed. The synthesis included a combination of prote cting groups that is generally applicable to oligonucleotide syntheses in combination with various 2'OH protecting groups. The protecting gr oups did not cause racemization of the amino acid residue of (acp)3U d uring deprotection. The assignment of all H-1 NMR resonances of modifi ed nucleoside-containing oligoribonucleotides includes heteronuclear o ne and two dimensional NMR.