A new approach for the synthesis of 3′-deoxy-3′-C-formyl-ribonucleosides and the synthesis of alternating methylene(methylimino) linked phosphodiester backbone oligonucleotides with 2′-OH and 2′-OMe groups

A stereoselective synthesis of 3′-deoxy-3′-C-formyl-5-methyluridine 2 is described via the dithiane 4 as the key intermediate. Compound 2 was coupled with 3 into a novel ribo-MMI dimer 1. The dimer was then incorporated into antisense oligonucleotides which were found to have high binding affinity to the target RNA.