Anhydrosugars structures

In the polymerization of anhydrosugars, however, it is desirable to prepare the polymers having the structure identical with that occurring in natural polysaccharidess. This can not always be achieved. 

The structures of the 1,6-anhydrosugars generated from different aldohexoses, indicating the steric arrangement of different OH groups, are shown below (C-H bonds not shown). 

One approach utilized in carbohydrate pyrolysis is Py-MS. Py-MS using El type ionization does not differentiate well between anhydrosugar stereoisomers, and its utilization to obtain structural information on carbohydrates is rather limited. However, there are reports [10a] where the type of bond between monosaccharide units can be differentiated using Py-EI MS. As an example, the Py-EI MS results are shown for a (1 -> 2)-p-glucan and for a (1 -> 3)-p-glucan (laminaran). 

Polysaccharides having a regular structure were first obtained by polymerization of anhydrosugars or step-by-step elongation. For synthesis of irregular structures, a step-by-step elongation by polycondensation is the usual method at least to produce the repeating unit which is then polymerized. These routes have been discussed previously in the review of Kochetkov (313). 

The bicyclic acetal, 6,8-DBO, possesses the structural skeleton of the 1,6-anhydrosugars and, because it is readily prepared from acrolein dimer, its cationic polymerization has been investigated. Mostly Lewis acids (BF3, PF5) were used as initiators, and at low temperature (-78 °C) polymers with Mn up to 10 could be obtained although dispersity was broad. ... 

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