Methyl periodate oxidation

Structural analysis of isolated amylose and amylopectin components has been carried out by standard methods based on methylation, periodate oxidation, and partial acid hydrolysis studies. Methylation and periodate oxidation studies established the linkage types and frequency of... 

The disaccharide nigerose is a-D-Glup-(l — 3)-D-glu. Write out its structure. How would you prove this structure using methylation, periodate oxidation, and other methods. 

Methylation of carminic acid with diazomethane in methanol gives a methyl ester tetramethyl ether in which the four phenolic hydroxyl groups are methylated. Periodate oxidation of one mole of this compound with sodium metaperiodate in the dark at 0° gives a rapid consumption of two moles only of oxidant, with the formation of some formic acid (unstated amount). These results show that the n-glucose residue in carminic acid must be pyranose. 

The manner in which the three amino sugar moieties are combined in kanamycin (8) was deduced from the results of methylation, periodate-oxidation, and partial-hydrolysis studies. Hydrolysis of kanamycin with 6 N hydrochloric acid at 100° for only 15 minutes yields, as shown by paper chromatography and by preparative chromatography, two disaccharide components which were shown to be 2-deoxystreptamine kanosaminide and 2-deoxystreptamine 6-amino-6-deoxy-D-glucopyrano-side. Thus, both of the aminodeoxyhexoses must be linked glycosidically to the 2-deoxystreptamine, and not one to the other. It is interesting to note that the amount of each disaccharide formed during the period of hy-... 

The simplest possible structure proposed for the cell wall glucan of Pyricularia oryzae, based on the results of methylation, periodate oxidation and fragmentation analysis is shown in Fig. 1. 

Phytohaemagglutinins.—Abrin, ricin, and their isolated A and B chains have been subjected to various chemical treatments and the effect of these on the biological activity of the lectins assessed. Reductive methylation, periodate oxidation, or succinylation of abrin or ricin reduced the toxicity and haemagglutinating ability of the former but not the latter. Treatment with A-acetylimidazole or A-bromosuccinimide resulted in strongly reduced toxicity of abrin and ricin, while 2-hydroxy-5-nitrobenzyl bromide had much less effect. 

On the basis of the results of methylation, periodate oxidation, and oxidative deamination with ninhydrin, the structure shown above is proposed 50, 51a, 611)) for the repeating unit of chondroitin sulfate A. 

Chemical evidence has indicated that the O-specific polysaccharide isolated from Shigella boydii has a pentasaccharide repeating unit containing D-mannosyl, D-galactosyl, 2-amino-2-deoxy-D-galactosyl, and D-glucuronic acid residues (2 1 1 1). The structure (10) was proposed for the polysaccharide on the evidence of methylation, periodate oxidation, and Smith degradation. ... 

A more eflicient and general synthetic procedure is the Masamune reaction of aldehydes with boron enolates of chiral a-silyloxy ketones. A double asymmetric induction generates two new chiral centres with enantioselectivities > 99%. It is again explained by a chair-like six-centre transition state. The repulsive interactions of the bulky cyclohexyl group with the vinylic hydrogen and the boron ligands dictate the approach of the enolate to the aldehyde (S. Masamune, 1981 A). The fi-hydroxy-x-methyl ketones obtained are pure threo products (threo = threose- or threonine-like Fischer formula also termed syn" = planar zig-zag chain with substituents on one side), and the reaction has successfully been applied to macrolide syntheses (S. Masamune, 1981 B). Optically pure threo (= syn") 8-hydroxy-a-methyl carboxylic acids are obtained by desilylation and periodate oxidation (S. Masamune, 1981 A). Chiral 0-((S)-trans-2,5-dimethyl-l-borolanyl) ketene thioketals giving pure erythro (= anti ) diastereomers have also been developed by S. Masamune (1986). 

Methylation of free OH groups, followed by denitration, hydrolysis, reduction, and glc analysis has been suggested as a method for determining the location of nitrate (82). This method has been suggested for CP and CS (82) as the phosphate and sulfate groups are stable to methylation and can then be removed. Periodate oxidation has been used to determine the DS of CS (81). 

Since aldehydes are notoriously polymerizable and difficult to manipulate, the products of periodate oxidation are oftentimes further oxidized, with hypohalite, to carboxylic acids, or are reduced to the corresponding alcohols. Oxidation has been more usually employed than reduction, since acids frequently form crystalline salts and other conveniently prepared derivatives. A process of oxidation of these aldehydic products by hypo-bromite, in the presence of barium carbonate or strontium carbonate, was developed and used extensively by Hudson and his coworkers.107 110 194-199,90s Their method can best be illustrated by an example the further oxidation of the dialdehyde, VI, shown previously (see p. 16) to be obtained by the oxidation of the methyl a-D-aldohexopyranosides. The isolation of... 

The rate of oxidation of ethylene glycol was found268-269 to attain a broad maximum between pH 2.5 and 6. In a very complete study of the effect of pH on the periodate oxidation of carbohydrates, Neumiiller and Vasseur260 showed that the oxidation of maltose, melibiose, methyl a-D-... 

XVIII has now been excluded,42 since the methyl glycoside of the sugar reacts rather rapidly with one mole of periodate per mole furthermore, in contrast to the behavior of mycaminose (XXI), no moiety with one carbon atom less has been isolated from the products of periodate oxidation. Oxidation of mycarose with hypoiodite affords a crystalline lactone with the empirical formula C7H12O4 this observation eliminates the possibility of the keto structure XX. Thus, mycarose appears to be a 2,6-dideoxy-3-C -methylhexose (XIX). In the original compound, the isovaleryl group must be esterified to the alcohol function at C4, since the methyl glycoside isovalerate obtained from carbomycin is only attacked by periodate after alkaline hydrolysis. 

Pacsu4 5 has suggested a structure for starch involving a small number of non-cyclic hemiacetal linkages, the number being presumably sufficient to account for the number of endgroups determined by the methylation method. Halsall, Hirst and Jones6 have commented on this structure, however, and have shown it to be incompatible with the results of periodate-oxidation studies. In addition, these authors pointed out that it would be difficult to explain enzymic hydrolysis and dextrin formation on the basis of such a structure. 

Table I shows the results of periodate oxidation and methylation applied to amylopectins from various sources. If the percentage of amylose in a whole starch is known, the length of unit chain of the amylopectin component can be calculated from the results of periodate oxidation of the whole starch (see Table II). The length of unit chain appears to depend on the botanical species, but not the variety, from which the starch wras isolated. In the case of tapioca and corn amylopectins, sub-fractionation of these by precipitation with methanol, followed by periodate oxidation, showed the sub-fractions had the same degree of branching as the original amylopectins.71 The action of periodate on whole starches and amylopectins is now so well established and accurate, that it may well completely supersede the methylation technique for pure starches, in view of its many advantages.

Periodate oxidation has also been applied to this component.7 81 108 Theoretically, this method should be more satisfactory than methylation, as formation of derivatives is not necessary. However, recent work suggests that the chain length of amylose comprises several thousands of D-glucose units rather than hundreds (see Section V, 2), and the accuracy of such... 

Starch source D. P.a from osmotic measurements Unit-chain length from methylation Unit-chain length from periodate oxidation No. of non-reducing terminal groups/ molecule References... 

---