STUDIES ON TRANSFER RIBONUCLEIC ACIDS AND RELATED COMPOUNDS. XLI. SYNTHESIS OF TRNA FRAGMENTS CONTAINING MODIFIED NUCLEOSIDES

tRNA fragments containing modified nucleosides have been synthesized either by condensation of nucleotides containing a modified base or by modification of oligonucleotides. Ribothymidine 3'-phosphate was prepared by condensation of the silylated base with protected D-ribose followed by phosphorylation. Ribothymidine-containing trimer, T-Ψ-C, was synthesized by the phosphodiester method. A ribothymidine-containing hexamer T-U-C-A-A-A and a 2'-O-methylcytidine containing hexamer C-G-G-G-Cm-Up were synthesized by the phosphotriester method. A dihydrouridine-containing trimer D-A-G and a 7-methylguanosine-containing trimer m7G-U-C were obtained by modification of the trimers by reduction and methylation, respectively.