Synthesis of a Novel trans-3’,4’-BNA Monomer Bearing a 4,8-Dioxa-5-azabicyclo[5.3.0]decane Skeleton

A novel trans-3',4'-BNA monomer, in which sugar conformation was restricted to S-type by a trans-fused 3-oxa-4-azapentylene bridge between C3' and C4' position, was designed and synthesized.The trans-fused 7-membered cyclic structure within a 4,8-dioxa-5-azabicyclo[5.3.0]decaneskeleton was prepared by means of intramolecular substitution reaction using potassium carbonate as a base.We found that all of protecting groups (benzyl, benzyloxymethyl, and benzyloxycarbonyl group) were able to be removed smoothly by DDQ oxidation followed by boron trichloride treatment without cleavage of N-O linkage to afford the desired trans-3',4'-BNA monomer.