A PRACTICAL SYNTHESIS OF N1-METHYL-2'-DEOXY-PSI-URIDINE (PSI-THYMIDINE) AND ITS INCORPORATION INTO G-RICH TRIPLE-HELIX FORMING OLIGONUCLEOTIDES

A convenient synthesis of N1-methyl-2'-deoxy-psi-uridine (psi-thymidine, psi T, 7a) has been accomplished in good yield. The structural conformation of 7a was derived by 2D NMR and 1D NOE experiments. The nucleoside 7a has been incorporated into G-rich tripler forming oligonucleotides (TFOs) by solid-support, phosphoramidite method. The tripler forming capabilities of the modified TFOs (S4, S5 and S6) containing psi T has been evaluated in antiparallel motif with a target duplex (duplex-31) 5'd(CTGAGACCGGGAAGGAGGAAGGGCCAGTGAC)3'-5d(GACTCTGGCCCTTCCTCCTTCCCGGTCACTG)3' (D1) at pH 7.6. The tripler formation of modified homopyrimidine-oligomers (S1, S2 and S3) has also been studied in parallel motif with a duplex-10 (A(10):T-10) at pH 7.0.