Formation of and Glycosylation with Per-O-Acetyl Septanosyl Halides: Rationalizing Complex Reactivity En Route to p-Nitrophenyl Septanosides

摘要

Protein-carbohydrate interactions are at the heart of many biological processes. For lectins, those interactions result simply in the association of two species, whereas for enzymes like glycosidases, association ultimately leads to cleavage and formation of covalent bonds. We have investigated lectin-septanose interactions in the past. Here we report on a route to synthesize p-nitrophenyl septanosides via the corresponding septanosyl halides. During the investigation we observed differential rates of glycosyl halide formation of the per-O-acetyl septanoses based on the stereochemistry at C1 and C2. Further, we observed unexpected stereoselectivities in glycoside bond formation that depended on a number of factors including the electrophilic sugar species, the incoming nucleophile, and reaction conditions. The results provided new parameters to consider when approaching septanose glycosylations. Even more importantly, the synthesis of p-nitrophenyl septanosides will enable them to be used to interrogate septanose-glycosidase binding and hydrolysis.