Sugar oxazoline

Synthesis of natural-type aminopolysaccharide having dibenzylchitin structure was achieved by the polymerization of a sugar oxazoline monomer, 1 having one hydroxy group at position 4 (Scheme 4) [9]. The polymerization was carried out with an acid catalyst in 1,2-dichloroethane solvent at reflux temperature. All the H-NMR, C-NMR, and IR spectra as well as elemental analysis data of the isolated polysaccharide supported that the polymerization proceeded by the stereoregular glycosylation to give (1 4)-... 

The polymerization using sugar oxazoline monomers is not limited to the synthesis of linear aminopolysaccharides as described above and can be extended to formation of a hyperbranched material. Synthesis of hy-perbranched aminopolysaccharide was achieved by acid-catalyzed polymerization of a sugar oxazoline monomer, 8, having two hydroxy groups at position 3 and 4, which can be considered as an AB2 monomer (Scheme 9) [12]. This is the first example of the synthesis of a hyper-... 

Fused or spiro sugar oxazolines have been synthesized by treating D-fructopyranose or D-fructofuranose 1,2-0-acetonides with nitriles in triflic acid773 (Scheme 5.73). First the activation of the anomeric center takes place with simultaneous isopropy-lidene cleavage to form the oxocarbenium ion intermediate, which is attacked by the nitrile. The resulting nitrilium ion is then trapped by the hydroxyl group in an intramolecular Ritter-like reaction to yield the final product. 

A new and mild method for opening sugar oxazolines, mediated by Cu(II) salts, was described, affording 2-acetamido-2-deoxy-p-D-glucopyranosides 177 in good yield <02EJO1363>. 

Sugar oxazolines can be oxidized with m-CPBA and subsequently with Dess-Martin periodinane into nitroglycal derivatives<02TL347>. 

Wittmann, V, Lennartz, D, Copper(II)-mediated activation of sugar oxazolines mild and efficient synthesis of (3-glycosides of A-acetylglucosamine, Eur. J. Org. Chem., 1363-1367, 2002. 

Scheme 1. Synthesis of di- and tetra-saccharide sugar oxazolines... 

Scheme 2. ENGase-catalyzed transglycosylation with synthetic sugar oxazolines... 

Figure 5. Structures of additional synthetic sugar oxazoline derivatives...

The present paper focuses on precision synthesis of natural HA (46) and Ch (47) with well-defined structures of biological importance, via hyaluronidase-catalyzed polymerization of sugar oxazoline derivatives (Scheme 1). Similarly, unnatural Chs (6) were prepared using the same enzyme (47) (Scheme 2). These reactions provide a facile and efficient approach to synthesis of GAGs with well-defined structures. 

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