Unusual C7- versus Normal 5'-O-Dimethoxytritylation of 6-Arylpyrrolocytidine Analogs.

Fluorescent deoxynucleosides possessing the modified bases 6-(2-benzo[b]furyl)- and 6-(2-furyl)pyrrolocytosine (BFpC and FpC) have been synthesized along with the quencher nucleosides possessing 6-{4-[(4-dimethylamino)azo]phenyl}pyrrolocytosine (DABCYLpC) and 6-(p-nitrophenyl)pyrrolocytosine (p-NO2-PhpC) nucleobase analogs. Standard treatment of BFpC, FpC, DABCYLpC, and p-NO2-PhpC with dimethoxytrityl chloride (DMT-Cl) led to the unusual substitution on the C7 of the pyrrolocytosine skeleton. The desired 5'-O-DMT-protected nucleoside analogs were synthesized from suitably protected 5'-O-DMT cytidines. Subsequent phosphitylation smoothly afforded BFpC-, FpC-, DABCYLpC-, and p-NO2-PhpC-derived monomers suitable for standard oligonucleotide synthesis.