Chemical Synthesis and Structure Proof of a Stereoregular Linear Mannan, Poly-α-(1→6′)-anhydro-D-mannopyranose

Stereoregular poly-α-(1→6′)-anhydro-D-mannopyranose has been synthesized by the phosphorus pentafluoride initiated polymerization of 1,6-anhydro-2,3,4-tri-O-benzyl-β-D-mannopyranose at –78˚ in methylene chloride, followed by debenzylation of the polymeric derivative with sodium in liquid ammonia. The polymer, isolated as a hemihydrate, [α]³⁰D 121.5-122.8˚ (1 % in DMSO), forms cloudy solutions in water and clear solutions in dimethyl sulfoxide. On periodate oxidation, this polymer consumes the theoretical amount of oxidant and produces the theoretical amount of formic acid. After oxidation the optical rotation of both the synthetic mannan and a synthetic stereoregular poly-α-(1rarr;6′)-anhydro-D-glucopyranose are identical. Less stereoregular mannas have been synthesized from the corresponding triacetate and after oxidation show lower positive rotations.