Synthesis of a comb-shaped branched polysaccharide via ring-opening polymerization of a reactive anhydro disaccharide derivative

Abstract

This paper deals with a comb-shaped branched polysaccharide, which has a linear backbone and pendant monosaccharide units regularly substituted on each sugar unit in the main chain.',' Naturally occurring polysaccharides often have branched structures, and their physical and biological functions are influenced by the nature of the b r a n~h e s .~ It has also been noted that branched oligosaccharides on glycoproteins and glycolipids in cell surface membranes are key participants in cell-cell recognition during de~elopment.~ In these respects, welldefined comb-shaped polysaccharides are expected to serve as model substances for physicochemical and biological studies and as cell-specific biomedical materials using carbohydrates as a recognition marker.5,6Synthesis of comb-shaped branched polysaccharides has been attempted by two different routes via ring-opening polymerization of anhydro sugar derivatives: (1) polymerizatioin of anhydro disaccharide derivatives followed by deprotection',' and (2) synthesis of regiospecifically protected linear polysaccharides followed by stereoselective glycosidation and d e p r o t e c t i~n .~,~ The former route is favorable for the synthesis of polysaccharides that are substituted completely and stereospecifically with monosaccharide moieties. However, anhydro disaccharide derivatives seem less reactive in polymerization than the corresponding anhydro monosaccharide deriva-ti~es,','*~and hence highly reactive disaccharide anhydrides are required to lead to high molecular weight polysaccharides.In this paper, we gave attention to the high polymerization reactivity of dideoxygenated anhydro ring structures'O and to the role of a P-galactopyranose unit as a recognition marker. According to Scheme I, these two moieties were coupled to give 1,6-anhydro-3-0-(2,3,4,6-tetra-0-benzyl-~-~-galactopyranosyl)-2,4-dideoxy-~-~-threo-hexopyranose (1). The ring-opening polymerization of 1 followed by deprotection of the resulting polymer (2) was carried out, and a well-defined comb-shaped polysaccharide, 2,4-dideoxy-3-0-(P-~-galactopyranosy1)-(1-+6)a-D-threo-hexopyranan (3) was obtained. The polymerization reactivity of 1 is discussed in comparison with those of analogous anhydrides and their parent compounds including 1,6-anhydro-2,4-di-O-benzyl-3-0-(2,3,4,6-tetra-~-benzy~-~-~-gaiactopyranosy~)-~-~-g~ucopyranose (41, 1,6-anhydro-3-O-benzyl-2,4-dideoxy-P-~threo-hexopyranose (5)," and 1,6-anhydro-2,3,4-tri-Obenzyl-s-D-glucopyranose (6). BnO ,OBn OBn OBn OBn OBn 4 5 6 0024-9297 I 9 0 12223-1884$02.50 I O Results and Discussion Synthesis of a Comb-Shaped Branched Polysaccharide, 2,4-Dideoxy-3-0-(&~-galactopyranosyl)-(1-.6)-a-~-thr~hexopyranan (3). Polymerization data of 1 are summarized in Table I. A relatively large amount of the initiator was required. The molecular weight of the disaccharide derivative was high (MW = 653), and hence the monomer concentration could not be made higher than those employed. The polymerization of 1 at -78 O C was more satisfactory than that at -60 "C in terms of pol...

Synthesis of Oligosaccharide‐Branched Ribofuranan by Ring‐Opening Polymerization of a New Anhydroribo Trisaccharide Monomer

“…1,4‐Anhydro‐ribose is one of the preferable anhydro sugar moieties for the ring‐opening polymerization because it has the highest cationic ring‐opening polymerizability 5, 6. The 3‐ O ‐substituted ribose monomer, A2B3LR, should be more reactive than that of 2‐ O ‐substituted monomer because it has lower steric hindrance at the anomeric position 15. The elementary analysis of A2B3LR was in good agreement with the calculated value.…”

A Monte Carlo simulation study on long-chain combs

“…Recently, welldefined comb-shaped polysaccharides have been synthesized to act as model compounds for physicochemical studies. 2 Other new variations involve grafting hydrophilic branches to a hydrophobic backbone3 and synthetic branches onto a backbone that is a copolymer of cellulose and starch.4 Finally, this topology is found in many examples of liquid crystal polymers. While such systems are usually studied in the melt or in nematic solvents, there has been some characterization of dilute solutions I I I I Figure 1.…”

Statistical and metric properties of long-chain combs

“…the logarithm of both sides and dividing by In N gives (1/ln N) In [cMcomb/(gSAWN)] ~(7c0mb -1) +N In (gcomb/MsAw)/^n N(5) …”