Sialic acids periodate oxidation/borohydride

After reduction of the aldehyde with borohydride, the ester groups of the remaining mono-, di-, and tri-O-acetylated sialic acids that are unaffected by these vigorous conditions of oxidation are hydrolyzed by alkali, the products are subjected to mild oxidation with periodate,... 

To investigate the latter possibility, sections of bovine submandibular gland and human colon were oxidized for periods of either 10 or 30 minutes and were then reduced with sodium borohydride. The sections were then reoxidized with periodate for various periods and then stained with Schiff reagent. The results obtained showed that when human colonic mucins were oxidized for an initial period of 10 minutes, some PAS reactivity could be regenerated by a second oxidation period of 60 minutes. When however, the initial oxidation period was extended to 30 minutes, no further PAS reactivity could be generated by a second period of oxidation. These results could be interpreted in two ways either they were the result of the incomplete oxidation of a relatively small number of 9-0-acyl sialic acids or the failure to oxidize other tissue diols. The probability of the latter was lessened by the observation that the oxidation of the crypt mucins of rabbit small intestine which do not contain 0-acylated sialic acids was apparently complete in 10 minutes. 

The influence of the C-7 to C-9 side chain of the sialic acid molecule on sialidase action has been demonstrated using complex carbohydrates subjected to mild periodate oxidation and subsequent borohydride reduction to yield C-7 and C-8 analogues of sialic acid. The progressive shortening of the chain led to a progressive decrease in bacterial and viral sialidase action (Suttajit and Winzler... 

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