Highly Efficient and Stereoselective Synthesis of 6,7‐Dideoxy‐β‐d‐ido‐octopyranuronates

Abstract

Abstract6‐Deoxy‐β‐ido‐heptopyranosides are challenging glycosides to synthesize due to their unusual 6‐deoxy‐heptose backbone, rare ido‐configuration and most importantly, the β‐1,2‐cis anomeric linkage. They are found in nature, such as being part of the repeating disaccharide of C. jejuni HS:4 capsular polysaccharides (CPs). Interestingly, the bacterial CPs is found to be partially modified with an O‐methyl phosphoramidate (MeOPN) functionality at the O‐2 or O‐7 position of the 6‐deoxy‐β‐d‐ido‐heptopyranosides. In this work, we report the first synthesis of three analogous of β‐d‐ido‐octopyranosides (1–3) that contain a 6,7‐dideoxy‐functionality and either a terminal methyl ester or carboxylic acid or amide. Since carboxylic acids have been reported as bioisosteres of phosphate group, compound 1–3 can be regarded as carbon‐based bioisosteres of 6‐Deoxy‐β‐ido‐heptopyranoside containing the MeOPN group without a chiral center. Compounds (1–3) were efficiently synthesized from a O‐2 activated β‐d‐galacto‐octopyranuronate (19) that was efficiently converted to the desired β‐d‐ido‐octopyranuronate configuration using an elegant one‐pot process.