Synthesis and Structure of New Methylene-Bridged Hexopyranosyl Nucleoside (BHNA)

Abstract

A new member of hexopyranosyl nucleoside family, methylene-bridged hexopyranosyl nucleoside (BHNA), has been synthesized through generation of carbon radical at C6' in (6'S-Me, 7'S-Me)-carba-LNA T nucleoside, followed by rearrangement to C4' radical which was quenched by hydrogen atom to give BHNA. The stereoelectronic requirement for this unusual radical rearrangement has been elucidated by chemical model building and ab intio calculations to show that the coplanarity of the single electron occupied p-orbital at C6' with σ*O4'-C4' plays an important role for the rearrangement reaction to take place. The solution structure of BHNA has also been studied using NMR as well as by ab initio calculations. The new six-membered pyranosyl ring in BHNA, unlike other known hexopyranosyl nucleosides, adopts a twist conformation, with base moiety occupying the axial position while 3'-hydroxymethyl and 4'-hydroxyl occupying the equatorial position.