Synthesis of an enantiomer of cellulose via cationic ring-opening polymerization

The enantiomer of natural “d-cellulose” (= “l-cellulose”), which consists of l-glucose, was synthesized from l-glucose via cationic ring-opening polymerization. l-Glucose (1L) was converted to 3-O-benzyl-2,6-di-O-pivaloyl-β-l-glucose 1,2,4-orthopivalate (6L) by five reaction steps. l-Glucose and its derivatives showed almost the same reactivity as d-glucose and its derivatives during the synthesis of compound 6L. Cationic ring-opening polymerization of compound 6L under atmospheric pressure proceeded smoothly to give 3-O-benzyl-2,6-di-O-pivaloyl-β-l-glucopyranan (7L) with a degree of polymerization (DPn) of 32.8 (Mw/Mn = 2.19). Removal of the benzyl and pivaloyl groups of compound 7L and subsequent acetylation gave acetylated β-l-glucopyranan. 1H and 13C NMR spectra of the acetylated β-l-glucopyranan had the same profiles as those of commercial cellulose triacetate prepared from natural cellulose, while its specific rotation was opposite, indicating the successful synthesis of l-cellulose. The synthesized l-cellulose had a cellulose II crystal structure. This is the first reported synthesis of l-cellulose, an l-polysaccharide that consists of an l-monosaccharide.