Periodate Oxidation and Smith Degradation

When periodate oxidation is combined with Smith degradation, further structural information, like glucan branching frequency, can be obtained [60], and has been used to help elucidate, for example, (1,3)(1,6)-P-glucan structure of Claviceps glucan [73], scleroglucan [74] and the glucan from Laetisaria arvali [75]. However, this usually requires more than one round of oxidation/degradation and a comparison of reaction products after each step [25]. Nonreducing ends are cleaved between C2/C3 and C3/C4, consuming a total of 2 mol of periodate and producing 1 mol of formic acid. The resulting polyaldehyde undergoes borohydride reduction forming a polyalcohol. Transformed nonreducing ends are now susceptible to mild acid hydrolysis and can be removed selectively [69] to give a linear (1,3)-P-glucan, glycerol (1 mol) and glycolaldehyde (1 mol).

Such oxidation/degradation reactions can clarify structural ambiguities of branched (1,3)-P-glucans as in Omphalia lapidescens [72]. Schmid [35] also used it to help resolve structural ambiguities in the branching frequency of the repeating unit of epiglucan from Epicoccum species where the data, consistent with those from 13C-NMR [36], supported single side branches on average at two of every three backbone glucosyl residues (Figure 3.1).

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