Synthesis of bradyrhizose, a unique inositol-fused monosaccharide relevant to a Nod-factor independent nitrogen fixation.

The symbiosis of Bradyrhizobium sp. BTAi1 with its host plant Aeschynomene indica relies on a Nod-factor independent mechanism, wherein the Bradyrhizobium O-antigen is regarded as a key factor. This O-antigen polysaccharide is composed of a unique C10 monosaccharide, namely bradyrhizose, which has a galactose-inositol trans-fused scaffold, via a homogeneous α-(1 → 7)-linkage. Herein, we report the first synthesis of bradyrhizose. The scalable synthesis requires 26 steps in a high overall yield of 9%, with the inositol scaffold being constructed effectively via a Ferrier II rearrangement from a fully functionalized C2 and C4 branched pyranose derivative.