Anhydro Sugars Containing 5-Membered Rings

2-displacement leads to the formation of 3-membered oxirane rings. Only a few anhydro sugars in this group have been polymerized, among them l,2-anhydro-3,4,6-tri-O-acetyl-D-glycopyranose (Brigl s anhydride)8). 

Polymerization of (8-8) with Lewis acid initiators involves opening of the oxirane ring and leads to low-molecular-weight polymers in addition crosslinked gel is 

Anhydro sugars containing an oxirane ring as a side-chain to the sugar moiety have also been polymerized by the cationic mechanism 9  

Polymerization of (8-9) proceeds by opening of the oxirane ring and leads, to a structure not occuring in nature. In this structure the sugar moiety is not a part of the main chain, but is a pendant group attached to the polyoxyethylene backbone. 

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Polysaccharides prepared from 1,4-anhydro sugars contain both pyranose (6-membered) and fiiranose (5-membered) rings in the main chain l2). The presence of both structures was established by hydrolysis which showed that either of the chemically equivalent, C-l-O-bonds may be broken during polymerization ... 

This difference in the AG values is especially observable in the temperature-dependent, nuclear magnetic resonance spectrum of 5,6-bis(acetamido)-l,6-anhydro-5,6-dideoxy-j8-L-idopyranose. This sugar contains a flve-membered and a six-membered ring amide in... 

In contrast to 1,4-anhydrides, the polymerization of 1,6-anhydro sugars with fused 5- and 6-membered rings, gives polymers containing exclusively pyranose rings in the main chain. 

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