Novel and facile synthesis of furanodictines A and B based on transformation of 2-acetamido-2-deoxy- d-glucose into 3,6-anhydro hexofuranoses
A novel synthesis of furanodictines A [2-acetamido-3,6-anhydro-2-deoxy-5-O-isovaleryl-d-glucofuranose (1)] and B [2-acetamido-3,6-anhydro-2-deoxy-5-O-isovaleryl-d-mannofuranose (2)] is described starting from 2-acetamido-2-deoxy-d-glucose (GlcNAc). The synthetic protocol is based on deriving the epimeric bicyclic 3,6-anhydro sugars [2-acetamido-3,6-anhydro-2-deoxy-d-glucofuranose (4) and 2-acetamido-3,6-anhydro-2-deoxy-d-mannofuranose (5)] from GlcNAc. Reaction with borate upon heating led to a facile transformation of GlcNAc into the desired epimeric 3,6-anhydro sugars. The C5 hydroxyl group of the 3,6-anhydro compounds 4 and 5 was regioselectively esterified with the isovaleryl chloride to complete the synthesis of furanodictines A and B, respectively. The targets 1 and 2 were synthesized in only two steps requiring no protection/deprotection.