Abstract
Cellulose, which comprises D-glucose and L-glucose (D,L-cellulose), was synthesized from D-glucose (1D) and L-glucose (1L) via cationic ring-opening polymerization. Specifically, the ring-opening copolymerization of 3-O-benzyl-2,6-di-O-pivaloyl-β-D-glucopyranoside (2D) and 3-O-benzyl-2,6-di-O-pivaloyl-β-D-glucopyranoside (2L), synthesized from compounds 1D and 1L, respectively, in a 1:1 ratio, afforded 3-O-benzyl-2,6-di-O-β-D,L-glucopyranan (3DL) with a degree of polymerization (DPn) of 28.5 (Mw/Mn = 1.90) in quantitative yield. The deprotection of compound 3DL and subsequent acetylation proceeded smoothly to afford acetylated compound 4DL with a DPn of 18.6 (Mw/Mn = 2.08). The specific rotation of acetylated compound 4DL was + 0.01°, suggesting that acetylated compound 4DL was optically inactive cellulose triacetate. Furthermore, before acetylation, compound 4DL was an optically inactive cellulose comprising an almost racemic mixture of D-glucose and L-glucose. Compound 4DL was an amorphous polymer. This is the first reported synthesis of optically inactive D,L-cellulose.
Highlights
Natural cellulose, which is the main constituent of plant cell wall, is a chiral homopolymer consisting of D-glucose
Cationic ring-opening copolymerization of glucose orthoester derivatives 2D and 2L Glucose orthoester derivatives 2D and 2L were synthesized from compounds 1D and 1L, respectively, according to previous reports (Adelwöhrer et al 2009, Yagura et al 2020)
Signals assigned to benzyl groups in the range of 7.20–7.32 ppm and pivaloyl groups in the range of 0.99–1.29 ppm were found in the 1H NMR spectrum of compound 3DL
Summary
Natural cellulose, which is the main constituent of plant cell wall, is a chiral homopolymer consisting of D-glucose (denoted as D-cellulose hereafter). This study describes the synthesis of D,L-cellulose with a racemic mixture of Dglucose and L-glucose (D-glucose/L-glucose = 1:1) as an optically inactive cellulose via a synthetic route using cationic ring-opening polymerization, as shown in Scheme 1. The reaction mixture was hydrogenated with vigorous stirring under H2 at atmospheric pressure and room temperature for 24 h, filtered through Celite 535RVS (Nacalai Tesque Inc.), washing with THF, and concentrated azeotropically with EtOH to give the partially debenzylated product as a colorless solid. This product was subjected to further debenzylation under the same conditions three times to obtain the fully debenzylated product as a colorless solid. Compound 4DL was acetylated with Ac2O/pyridine at 50 C for 12 h, and subjected to specific rotation, GPC and 1H/13C NMR measurements
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